Friday, December 19, 2014

Saturday, December 13, 2014

Take it from me: all dogs go to heaven

Apparently garments are being rent (by journalists if not by pet owners) over the revelation that Pope Francis never said pets go to heaven.  Maybe the pope won't say it, but you can take it from me: if you should ever find yourself in heaven in the afterlife, I promise that your beloved fido will be there too.  So sleep soundly.

Friday, December 12, 2014

The cure for ebola

Remember, you heard it here first, folks.  The cure for ebola is described in this paper, published in the World Journal of Critical Care Medicine last May.

So why hasn't anybody noticed?  Well, for starters, it's not just a cure for ebola, but a host of other conditions that kill a lot more people than ebola, including septic shock.  That puts is squarely in the too-good-to-be-true category that would make anyone hearing this news for the first time rightfully skeptical.  But I've looked into it, and it seems plausible.  The theory is that it is not the infections that do the damage, it's the metabolic by-products of your immune system fighting the infections, and specifically a buildup of hydrogen peroxide.  If you intervene to get rid of the peroxide then you can keep the patient alive long enough for the body to finish fighting off the infection.  And there is a drug already on the market that does exactly that, though it is currently used for a different purpose.  (I've been asked by Jay Pravda, the author of the paper not to reveal what this drug is.)

If anyone reading this happens to know someone doing field work with ebola victims in Africa and would be willing to put me in touch with them please drop me a line.  There's a fairly straightforward experiment that could be done to test Dr. Pravda's theory (check ebola victims for elevated levels of hydrogen peroxide in their bloodstreams) and I'd like to do what I can to get this experiment done sooner rather than later.  The situation is too urgent to just let the usual processes run their course.

Tuesday, December 09, 2014

Yet another reason never to fly Korean Air

Aside from the fact that Korean pilots are incompetent, a KAL executive today ordered a flight to return to the gate because she didn't like how her macadamia nut were served.

Freaking out about how your nuts are served is bad enough, but delaying an entire planeload of passengers simply because you can is way beyond the pale.

The AP (via ABC news) reports:
[The executive in question] is the oldest child of Korean Air's chairman, tycoon Cho Yang-ho. Her two siblings are also executives at South Korea's largest airline.
As the mechanic who opened the hood of the car to find the engine missing said, "Well, there's yer problem right there."  And the way things are going at KAL it would hardly surprise me to see that scene actually played out there.

Tuesday, December 02, 2014

Quantum teleportation demystified

About a week ago, NASA's Jet Propulsion Lab, where I used to work, published this news item about an advance in quantum Teleportation.  The progress reported in the story is real, but the description of quantum teleportation presented in the article is misleading at best.  Yes, there are certain compromises that you have to make when describing quantum mechanics to a lay audience, but you don't have to actually lie to them, which is what the cartoon at the beginning of the article does.

Here's a recap of the description of QT in the cartoon:

  1. Alice has a yellow photon
  2. Charlie has a pair of blue photons that are entangled
  3. Charlie sends one to Alice
  4. And one to Bob who stores it in his crystal memory bank
  5. Alice and Bobs relationship is cordial but somewhat distant
  6. As the blue photon Alice received collides with her yellow photon she measures the event and learns that the state of her photon has been teleported to Bob's
  7. Alice's measuring of the event affects Bob's far-away photon, changing its state
  8. However, Bob can't determine that his photon has been changed
  9. until Alice sends him two bits of information over an optical fiber
  10. And Bob learns his photon has changed from blue to yellow too!

There are so many problems with this description that it's hard to know where to begin, but the most egregious is the last step.  It is not true that Bob "learns" that his photon has changed state from Alice's bits.  Bob has to manipulate his photon in order to make its state the same as Alice's original photon.  The two bits that Alice sends to Bob are instructions on how Bob should manipulate the state of his photon.  In the parlance of the cartoon, Alice measures her photon and discovers that it's yellow.  She then sends a message to Bob: "Make your photon yellow."  Bob does this, and lo and behold, Bob's photon, which used to be blue, is now yellow, just like Alice's original photon.

Of course, when you add this step, the whole process seems a whole lot less mysterious and newsworthy.  In fact, it seems completely mundane.  Why even bother with the entangled photons in the first place?  Well, it's because photons are weird.  They are not either blue or yellow.  That is too simple of a model.  Photons can be blue and yellow (in the parlance of the cartoon) at the same time.  But even that doesn't really capture the truth.

A better model of a photon is a coin: there's a heads side and a tails side, but you can only ever see one or the other.  You can't look at both sides at the same time.  These photon-coins are like vampires: they don't cast reflections in mirrors.  And if you try to enlist the help of an accomplice to look at the tails side while you look at the head side, the coin vanishes.  Try as you might, you can never see both sides at once.

So you look at the heads side and it's yellow.  You turn the coin over to look at the tails side and it's red.  You turn the coin over to look at the heads side again and suddenly it has changed from yellow to blue!  You turn it over again, and the tails side, which was red, is now green.

You do this a zillion times and you discover that the coin behaves in the following way:
  1. Every time you look at the heads side, it is either blue or yellow.
  2. Every time you look at the tails side, it is either red or green.
  3. Every time you turn the coin over, the color you see bears no relationship to the color you saw on that side the last time you looked.  As far as you can tell, the color of the newly revealed side is always completely random.
  4. However, you never actually see the coin change color.  Whatever side you are looking at stays the same color until you turn it over to look at the other side.
You also have a magic coin vending machine: you put one coin in, and two coins come out.  (Let us call this Vending Machine D for Duplicator).  Each one is half the size of the original, and they come out of the machine edge-on so that you can't see either side.  But each of these smaller coins behaves exactly like the larger coins did: the heads side is always blue or yellow, the tails side is always red or green.  But here's the kicker: if you take a pair of coins that just came out of Vending Machine D and turn them both over the same way (i.e. both heads or both tails) the colors on the two coins will always be the same.  But this is true only the first time you look at any given pair of coins.  After that the coins lose their magical connection and their colors are just random when you turn the over again.

What quantum teleportation does is allow you to transfer the magic connection from a pair of half-size coins from Vending Machine D to a pair of (previously unconnected) full-size coins [1].  It uses two additional vending machines, which I will call Vending Machines A and B.  Vending Machine A is on Alice's side, and Vending Machine B is on Bob's side.

Vending machine A has two coin slots, one for a full-size coin and one for a half-size coin.  It also has a display that flashes a number between 1 and 4.  Alice inserts her coins and notes what number the machine flashes.  She then calls Bob on the phone and tells him what the number was.

Vending machine B has a single half-size coin slot, and a knob with four settings numbered, as you might expect, from 1 to 4.  Bob sets the knob to the setting corresponding to the number that Alice told him on the phone.  He then inserts his half-sized coin, which the machine spits right back out.  (Whether or not this is the "same coin" turns out to be a Very Deep Question which we will ignore here.)  Like Vending Machine D, this half-size coin comes out edge-on, so Bob can choose whether to look at the heads side or tails side first.  Whichever he chooses, the color will be the same as that on the corresponding side of the full-size coin that Alice inserted into Vending Machine A.

That is a much more accurate description of quantum teleportation, and I think it's one that a layman is capable of grasping.  So why didn't NASA describe it that way?  Well, I asked them.  I sent an email to the contact person listed on the article, and here is the response I got:
Hi Ron, I very much appreciate your feedback. I took it back to the
scientists and they explained while the photon would not be initially blue
per se, we made this choice ‹ to say that the photon is initially blue ‹
to communicate the broad idea for the public. The question of at which
moment the photon is ³changed² cannot be answered with quantum mechanics
and is too subtle a point for our purpose, which is to give the public a
general sense of this experiment.
To which I responded:
> The question of at which moment the photon is ³changed² cannot be answered with quantum mechanics 
Yes, it can. And actually, this points out another problem with your presentation: when Bob receives Alice’s bits, he uses that information to apply one of four transformations to his photon. It is Bob’s action that changes his photon’s state into the state of Alice’s original photon. And that is the *only* time that Bob’s photon changes state. 
> and is too subtle a point for our purpose, which is to give the public a general sense of this experiment.

I think you underestimate your readers, and do them (and NASA) a grave disservice by not telling them the truth, particularly since this particular non-truth makes quantum teleportation seem much more mysterious than it really is. At the very least you should explicitly say that your presentation is an oversimplification, and give your readers a pointer to where they can get a more accurate explanation. I would be happy to write up a more accurate (but still accessible) description of quantum teleportation if you don’t have the time to do it yourself.
I never got a reply to that, which is what motivated me to publish this explanation here.

It frustrates me to no end that the popular press continues to publish false and misleading information about quantum mechanics in general, and about entanglement in particular.  There is no legitimate reason for it.  So why do they do it?  Well, the description in the NASA article is certainly more dramatic and mysterious.  For starters, it sounds a lot more like "real" teleportation than the more accurate description.  The fact that Alice has to send Bob instructions on how to set the dial on Vending Machine B takes a lot of the charm out of it.  In fact, you have to think pretty deeply about the behavior of the coins in order to see why quantum teleportation is interesting at all.  After all, why can't the four settings of the machine simply be an encoding of the colors on the two sides of the coin?  To answer that question you have to get into a discussion of the Bell inequalities, but that can also be done in a way that is accessible to laymen.

So why does the popular press so consistently get this wrong?  And why does the physics community let them get away with it?  Quite simply (I conjecture) because physicists think that it's good for business for the public to perceive what they do as indistinguishable from magic.  But for scientists to allow misinformation to promulgate is hypocritical, and fraught with all manner of peril.  When physicists endorse nonsense like "Alice's measuring of the event affects Bob's far-away photon, changing its state" on the grounds that it's a harmless white lie, it makes it that much harder to combat the not-so-white lies.  In a world where rejecting science can pose existential threats, deliberately obfuscating the truth is not a trivial transgression.  The fact of the matter is that quantum mechanics is not the intractable mystery that it has been made out to be, and allowing this perception to persist for the sake of grant money is making a deal with the devil.

[1] Since I just got finished ranting about the evils of allowing scientific misinformation to promulgate I should point out that this is slightly inaccurate.  Quantum teleportation does not transfer the magic connection to a pair of previously unconnected coins, it transfers it from one member of a pair of connected coins to one previously unconnected coin.  Of course, you can do this process twice in order to produce the effect as I describe it, so I submit that this really is a white lie.  But I will let you, gentle reader, be the judge of that.

Tuesday, November 11, 2014

Yet another reason to despise Groupon

Aside from being parasites, they are now brazenly trying to steal the GNOME Foundation's GNOME trademark.


[UPDATE:] Groupon backed down in the face of public pressure.

The coolest thing ever, again

I thought this photo of Saturn from above was the coolest thing ever until I saw this:

That is a picture of a comet.  Not in the background, mind you, the foreground.  It was taken by the Rosetta spacecraft, which is currently in orbit around said comet (which is burdened by the unwieldy name of 67P/ Churyumov-Gerasimenko).  The scale is just under a meter per pixel.  If there was a human walking around down there, you could see her (just barely).  The photo is about 800 meters (half a mile) from side to side.

In the next few days, a lander will detach from the spacecraft and, if all goes well, will actually land on the surface of the comet.  This will be only the fifth place in the universe from which we will have photos from the surface, the other four being the moon, Mars, Venus, Titan (one photo), and of course, Earth.

My nominee for second-coolest-thing-ever is this awe-inspiring backlit shot of Saturn:

You can find more of these at the Cassini images hall of fame.

It is truly an amazing universe we live in.  (Too bad we're blithely destroying the best part of it.)

Tuesday, October 14, 2014

Harris, Aflek, Dawkins, oh my!

It's been a busy couple of days for people who like to opine on the evils of Islam and Islamophobia.  Sam Harris and Ben Affleck kicked things off with a segment on Bill Maher's show where they had quite the scuffle over whether or not Harris was justified in his anti-Islamic rhetoric, or whether Affleck was trying to deny the truth in the name of political correctness.

Lots and lots and lots of people weighed in after that, and there are so many logical fallacies being brandished on both sides that it's hard to know where to begin.  For example, from Reza Aslan we have an argument from authority:
Sam Harris, to me, gives atheism a bad name because he comes from a tradition of atheism that is really disconnected from the titans of intellectual, philosophical atheism who gave birth to the modern world. These were experts in religion who, from a position of expertise, criticized religion. Sam Harris is a neuroscientist; he knows as much about religion as I do about neuroscience. The difference is that I don’t go around writing books about neuroscience.
Hemant Mehta follows up with some ad hominems:
Aslan seems to suffer from a mix of neediness (brought on by insecurity) and outright hubris. It might be a defect of his imagination ...
Guy Harrison offers up a straw man:
Reading the Koran and being aware of its potential to inspire some people to violence do not lead me to fear every Muslim on Earth
Surprisingly, Richard Dawkins starts out by being the voice of reason:
“Religion itself is not responsible for this… It’s also this feeling of political involvement. It’s a feeling that it’s ‘us against them.’ And I think that quite a large number of young Muslims feel kind of beleaguered against the rest of the world. [Emphasis added.]
Indeed.  Alas, he does not go on to ask the obvious question: how much of this beleaguerment might be attributable to the kinds of blanket statements that are made by the likes of Harris and Dawkins?  Instead he jumps straight to affirming the consequent:
And so religion in some sense might be just an excuse, but I do think that a dominant part of the motivation for these young men has to be religion.”
For a community supposedly dedicated to reason, the amount of unreasonableness being un-self-reflectedly bandied about is truly disheartening.

Utterly lost in the confusion is this central claim raised by Aslan:
There is a fundamental misunderstanding among these critics of religion in that they believe, first and foremost, that people get their values, their morals from their scripture, when in reality the exact opposite is true. You bring your morals and your values to the scriptures; you don’t extract them from them.
I don't want to take a side here on whether or not this claim is true.  I believe it is, but that's not the point.  The point is no one is talking about this despite the fact that it's the most important thing that got said in the entire discussion.  Why?  Because if it's true then Harris & co. are wrong, and if it's false then Aflek & co. are wrong.  So why is so much ink being spilled slinging logical fallacies around and absolutely no effort is going into determining the truth or falsity of a crucial empirical claim that could actually inform the debate?  Perhaps atheists, too, bring their prejudices to the scriptures (or the data) rather than the other way around.

So to lead by example, I'd like to offer up an actual data point.  That link goes to the Wikipedia page on the application of Sharia law by country.  I don't have time to slice-and-dice the numbers, but even a cursory glance will show that although there are major populations of Muslims all over the globe, those countries where Sharia law is in full effect are overwhelmingly found in the Middle East.  Last I checked, the Quran is the same all over the world, so this seems to me to be very strong evidence that the violence and barbarism often associated with Islam (and, to be sure, that's a very real problem) cannot be accounted for merely by the words in the Quran.

But I don't have a Ph.D. in religious studies, so what do I know?

Parallel universes and the arrow of time

In a previous post about quantum mechanics and parallel universes I ended with a puzzle:
All measurements are in principle reversible. Imagine that we could actually carry out this program of undoing the myriad entanglements that constitute your making a particular observation. What would be the subjective sensation, i.e. what would it "feel like" if this were done to you?
If you haven't read the previous post, please do before you read the rest of this one, otherwise this won't make any sense.  The point of this puzzle is not the answer, but the process by which one arrives at the answer.  Knowing the answer and understanding why it is the right answer are not the same thing, and in this case the latter is much more important than the former.

The intuitive answer to the question is that it would feel something like having time run backwards, but this is wrong.  The reason it is wrong goes to the very heart of the nature of reality.  To prime your mind to accept that the answer I am going to give is in fact correct I'm going to start by giving you the answer to what seems like it should be a completely different problem but is in fact almost exactly the same problem.  It is a classic problem first contemplated by Albert Einstein: what would it feel like to travel at the speed of light?

The intuitive answer to this question is that it would feel like a thrill ride, like zipping through the universe really, really fast.  Pluto is about four light-hours away, so if you headed towards it at the speed of light you'd get there four hours later, right?  How could it possibly be otherwise?

The unintuitive but undeniable fact of the matter is that the speed of light is the same in all reference frames.  This was shown experimentally in 1887 by the Michelson-Morley experiment, but it was actually predicted by James Clerk Maxwell 23 years earlier, in 1864.  Maxwell's equations for electromagnetic fields predicted the existence of electromagnetic waves that propagated at the (already well known) speed of light, but the equations made this prediction without any mention of a frame of reference.  The significance of this was not understood except in retrospect: it was forty years before Einstein first took the mathematical prediction and the experimental verification seriously and derived the theory of relativity, which can be summed up in the following pithy slogan: the speed of light is the universal reference.  Everything is always moving at the speed of light through space-time.  When you move faster through space you move slower through time.  When you move through space at the speed of light, time stops.  So what it would "feel like" to travel to Pluto at the speed of light is not that it would take four hours, but that you would get there instantaneously.  In other words, you would arrive at the same time that you left.

Now, an interesting thing happens if you arrive at the same time you left, and that is that you can no longer distinguish between leaving and arriving.  A trip from earth to pluto at the speed of light is indistinguishable (to the traveller) from a trip from pluto to earth at the speed of light.  Both consist simply of being at earth and pluto (and everywhere in between) at the same time (in the traveler's reference frame).  How do we reconcile this with the fact that an observer back on earth can easily tell the difference between a beam of light traveling in one direction rather than the other?

Here's a clue: the solutions of Maxwell's equations that predict electromagnetic waves are time-symmetric, that is, they predict the existence not only of waves traveling at the speed of light c, but they also predict waves traveling at speed minus c, that is, waves that move backwards in time.  These solutions are usually discarded out of hand as being "unphysical", but if Einstein teaches us anything it is that discarding mathematical results just because they don't "feel right" can blind us to deep truths.  (And indeed, if we take seriously the idea that there are electromagnetic waves moving backwards in time what we end up with is a completely self-consistent theory called the transactional interpretation of quantum mechanics.)

So what happens in QM if we really take the math seriously?  Well, we end up with a deeply unintuitive but nonetheless self-consistent description of the universe (except near a black hole -- physics is still working on that).  The math tells us that our classical reality is merely an approximation of the underlying metaphysical truth, just as Galilean relativity (where space and time are separate things) is.  The reason we think particles exist is not because they really exist, but because when you slice-and-dice the wavefunction in a certain way you end up with something that acts like (but isn't really) a bunch of classical entities all of which agree on a set of measurements (i.e. are in classical correlation with each other).

But, like Maxwell's equations, the Schroedinger equation is time-symmetric.  You can run it backwards as well as forwards.  And if you throw relativity into the mix then space and time are equivalent, and you can't distinguish forwards versus backwards any more than you can left versus right or up versus down.  In other words, the wave function is a static four-dimensional "thing" (for want of a more general noun) out of which space, time, and classical reality "emerge" when you slice it up in certain ways.  But there is nothing in the math that says that the slice that we are living in (what we call classical reality) is in any way special.  You can slice up the wave function in a different way and get a different universe.  All of this seems to be very much at odds with the (apparently) undeniable truth that our universe is special (at least to us), and that time only moves in one direction.

But again we must be very careful about trusting our intuitions, which have been proven wrong time and time again (the pun being a quantum superposition of intended and not :-)  The math says time doesn't "flow", just as it says particles aren't real.  So why does it appear to flow?

Again, we will approach the issue of time obliquely by drawing an analogy with particles.  Why do we think particles exist?  Because we can measure them.  But QM tells us that the results of our measurements indicate the presence of particles despite the fact that there are in fact no particles (or, if you're a multiple-worlder, that there must be other universes).  Let us go through the exact same mental exercise with respect to time: why do we think that time moves in one direction?  Because there is this manifest asymmetry: we can remember the past, but we can't remember the future.  And it's not just us: the universe "remembers" the past but not the future, which is to say, the universe contains information about the past (in books, for example) but not about the future.

There is another way to describe this asymmetry: we can "travel" forwards through time but we can't travel backwards.  Except that we actually can (in principle) "travel backwards in time" by "rewinding the universe" i.e. undoing all the entanglements that led to the present situation.  So let us go back and consider the opening puzzle: what would it feel like to "travel backwards in time" this way, to have yourself "reversed"?  Picture the scene: you would have to go into a sealed chamber of the sort that houses Shroedinger's cats.  Once safely ensconced inside, you would make some kind of measurement.  It doesn't really matter what kind, but let's suppose you made a quantum measurement just to keep things simple.  So there is some particle in the box with you, and you arrange for that particle to become entangled with some measurement apparatus and thence with your brain.  Your brain is now, by virtue of having become entangled with the particle in the having-observed-the-particle state.  You can remember making the measurement.  You know what the result of the measurement was.  All of the atoms in your brain are now acting together to make you appear like a classical system in classical correlation with itself and the measuring device.  This is what makes you think you know the state of the particle (even though in reality there is no particle).

Now we turn on the magic reverse-o-matic ray.  One by one, all of the entanglements that led you to be in the having-observed-the-particle state are undone.  This involves reversing the entanglements in your brain, the measuring device, and everything else inside the box (including the magic revers-o-matic ray, but since this is a thought experiment we can ignore the obvious difficulties that entails).  When this process is over, what mental state are you in?  Well, you are in exactly the same mental state that you were in before the whole process began.  You have no memory of having measured the particle.  You would have no memory of having the reverse-o-matic ray turned on.  And since completing the erasure involved undoing all of the entanglements in the box resulting from the initial measurement, you would not be able to find any evidence anywhere inside the box that any of this had happened.

In other words, the subjective sensation of undergoing a macroscopic quantum erasure is exactly the same as the subjective sensation of having nothing happen to you at all!  In fact, the only evidence that you would have that you had in fact undergone a quantum erasure is that when you emerged from the box after the experiment, you would find that more time had elapsed there than could be accounted for by what you experienced.  (Note the similarity to relativistic time-dilation.  Exercise: what would happen if you took a clock inside the box with you?)

So this is an unsatisfying sort of time-travel because it is experimentally indistinguishable from the normal state of affairs.  What we really mean when we fantasize about time travel is moving into the past with the information contained in our brains and bodies intact.  In other words, we're thinking about transporting information about the present into the past, at which point it becomes information about the future.  We think this might be possible because we think we're classical entities, coherent material things that move volitionally through space but are swept inexorably through time by some sort of "flow", and if we could just figure out how to "move through time" the way we move through space that we might be able to swim against the tide.

But we are not classical entities.

To understand the truth you need to adopt a completely different mindset about what you are.  Again, I will approach this obliquely starting with a more familiar concept: you think you're a human being, a physical entity with some coherent identity that remains intact through changes like growing older and learning new things.  (It is this abstract identity that we imagine moving into the past when we fantasize about time travel.)  What does this identity consist of?  It can't be the atoms in your body because those are constantly being swapped out for new atoms.  Maybe it is the arrangement of those atoms, at least at some high level of abstraction.  But the arrangement of your atoms today is radically different from what it was the day you were born.  In what sense, then, are you the "same person"?

The reason we consider ourselves to be in some sense the "same person" throughout our lives is because there is a continuous sequence of "yous" that lead from cradle to grave.  You today may be radically different from when you were born, but in between there is a smooth transition from one to the other.  At any instant in time, the you of that instant is very similar to the you one second previously, and very very similar to the you one Planck time earlier.

Imagine for a moment that you could take a God's-eye view of the universe and see all four dimensions at once.  Consider two different instances of "you" at two different times.  Is there any way you could tell which is the "earlier" you and which is the "later" you?  If the two times are far apart then you could look at which you appears older, but what if the times were just, say, a minute apart?  Well, you could still tell (if you were God) by examining your mental state: the later you would contain information that the earlier you didn't, namely, memories of the events that transpired during the intervening minute.  In fact, if you were presented with an unordered set of all the you's that have ever existed you could easily reassemble them in their proper order simply by looking at which ones contain information about which other ones.  If You-A remembers You-B then You-A must come after You-B.  It can never be the case that You-A remembers You-B and You-B remembers You-A because then one of those you's would be "remembering" the future, and that's not possible.

But the crucial point is not that it is impossible but why it is impossible.  The reason it is impossible is not that time only "flows" one way (that explanation would beg the question).  The reason it is impossible is that memories are entanglements just as measurements are.  In fact, memories are measurements, because every memory is a memory of something.  So it is not that a memory can't be reversed (it can), it is that in order to reverse a memory you have to reverse all the entanglements that comprise that memory.

Now, here's the killer question: given that the observable result of undergoing quantum erasure is indistinguishable from having nothing in particular happen to you at all, how can you be sure that at some point in your life it hasn't happened to you?

The answer is: you can't be sure it hasn't happened to you!  It is possible that you (and the rest of the universe) have undergone quantum erasure at some point.  In fact, it's possible that it happens regularly, that the entire universe is constantly being rolled back and replayed from different points in "time".  In fact, the universe is chock-full of little quantum "isolation boxes" where this happens constantly!  These are called "vacuum fluctuations" or "spontaneous pair generation", where a particle and an anti-particle just materialize out of nothing and almost immediately annihilate each other.  The members of a spontaneously generated pair are entangled.  The annihilation process "undoes" the entanglement and returns the universe to its previous state.

The punch line is this: the statement that we can't time-travel into the past is exactly the same as the statement that we can only remember the past.  It is not the case that one causes the other, it is that the two things are logically equivalent.    Your perception of "traveling through time" emerges from your mental states and not the other way around.  You feel like you are "traveling forward through time" because your mental states have this natural order to them.  You can remember the past and not the future because whatever you remember is your past.  The laws of quantum mechanics (and entanglement in particular) insure that what any given instance of you remembers appears to be a continuous and coherent sequence that behaves according to regularities that we call the laws of physics.  But in fact you do not travel through time, because at root there is no you, and there is no time.  There is only the wavefunction, from which you emerge as an approximation.

Wednesday, October 08, 2014

It's over

Salon has a pithy summary of the gay marriage scoreboard:
On Monday, the Supreme Court denied review to seven gay-marriage cases, allowing lower-court rulings in favor of marriage equality to stand. In effect, this brought the tally of states recognizing same-sex unions from 19 to 30. Then yesterday, the Ninth Circuit Court of Appeals found gay-marriage bans in Idaho and Nevada unconstitutional; with Alaska, Arizona, and Montana also under the Ninth Circuit’s jurisdiction, gay-marriage bans in those states are expected to fall easily, bringing the tally of states recognizing gay unions to 35.
That is a staggering turnaround.  Two days ago, there were 19 states where gay marriage was legal.  Now that number is 35.  In other words, there are now fewer states that don't allow gay marriage than did allow it two days ago.  If this were a football game, there would still be some time on the clock, but the fans would be leaving the stadium.

While I hesitate to declare victory prematurely, I really can't see any possible way that this could turn around now.  The score in terms of lower court decisions is 40-2, with only lower courts in Louisiana and Tennessee coming down (unsurprisingly) on the side of continuing discrimination against gays.  The worst-case scenario is that the fifth or sixth circuit will uphold a gay marriage ban, at which point SCOTUS will no longer be able to duck the issue the way they did on Monday.  But it is inconceivable that SCOTUS will reverse the overwhelming majority of lower court decisions.  By the time the case comes around to them again (if it does) there will be tens of thousands, maybe hundreds of thousands, of married gay couples all over the U.S.  They will be in California and Massachusetts and Kansas and Utah.  (Utah!)  They will be in Nevada and Oklahoma and Virginia and Illinois and New Mexico.  They will be in Pennsylvania and Maine and Vermont and Rhode Island.  They will be in... well, you get the idea.

They will even be in Texas and Tennessee and Louisiana and the twelve other holdouts for bigotry, because people move in this country.  And not a single one of those states will be able to show any actual harm that has been done to anyone by letting gays get married.  Zero.  Zip.  Nada.  That is, and has always been, the central issue.  All of these chicken-little predictions of the horrible consequences of gay marriage have been -- always have been -- wrong.  And now that wrongness has been removed from the realm of speculation and has become demonstrable.

If there is doubt in anyone's mind that this war is over, they need only look at the latest poll numbers among 18-39 year olds.  In that demographic, support for gay marriage is an overwhelming 72%.  Anti-gay bigotry in the U.S. is, quite literally, dying.

Good riddance.

Saturday, September 20, 2014

Some Christians show their true colors

Apparently, some Christians really can't stand religious freedom.

It's a beautiful piece by Hrafnkell Haraldsson (sic -- I cut-and-pasted the name from the original.  I gotta wonder how it's pronounced).  Here's my best shot at extracting a pithy quote:
Just the mere fact of somebody else practicing their religious beliefs is hateful to fake Christians to the extent that they insist those practices must be banned. And it isn’t just Satanism. You remember Bryan Fischer’s horrified objection to the Obamas letting actual Hindus into the White House to celebrate the Festival of Lights.
Well worth reading the whole thing.  And actually, the piece linked to in this quote is worth reading too.  It's one thing to know that there are hypocrites out there seeking to establish a Christian theocracy in the U.S. in the name of "religious freedom", quite another to witness it with your own eyes.  It is a horrifying spectacle indeed.

Wednesday, September 17, 2014

ISIS is a physics demonstration in guerrilla form

All you need to know about ISIS from Gary Brecher, the war nerd, over on Pando Daily.  I thought this passage was particularly noteworthy:
It’s amazing how well combat selects for talent. Nothing rewards talent less than a peacetime army, and nothing rewards it faster than an army actually in combat. And irregular forces, which usually suffer something like a 10:1 casualty rate against conventional occupiers, go through a nightmare-quick selection process. 
ISIS went through a lot of commanders before one stuck. He was a product of Islamic schools and US prison camps. He called himself Abu Bakr al Baghdadi, which means exactly nothing except that he’s claiming to be from Baghdad. He got out of prison in 2009 and walked into a leadership vacuum created by an airstrike which killed his predecessor—nothing like airstrikes to make room at the top—and oversaw ISIS’s move away from pressure once again, out of the cities toward the deserts of Anbar Province where Sunni sheikhs maintained strong clan networks. It wasn’t much, but it was a safe base, and that’s something any mixed militia/guerrilla force requires. 
ISIS got its second great break when The Syrian Civil War exploded in 2012. They looked west, across the Anbar deserts, and saw a huge organizational opportunity opening up in Syria. Assad’s troops had abandoned most of Eastern Syria to focus on defending the Alawite heartland along the coast. That vacuum created an opportunity for lots of people: The Syrian Kurds, who occupied a tier along the Turkish border in the northeast; dozens of local mafia/resistance groups, who mobilized to profit from the wide-open borders; and the nucleus of ISIS, who saw a chance to set up a little emirate in this new no-man’s-land in the wastelands of eastern Syria, along the borders with Anbar. 
That’s the key here: ISIS is a physics demonstration in guerrilla form. It began as a Jordanian insurgent group. Jordan was too tough to crack, and the group was under deadly strain until Bush and Cheney gave it new life with the 2003 invasion. It moved into Iraq, first to the north, in Kurdistan, and then, as the pressure grew up there, to the south and west, landing in Anbar. And when a new low-pressure system opened up to the west in Syria, ISIS flowed into it like a rain cloud—right along a natural pathway, the Euphrates River, which flows eastward into Anbar from Syria.
Well worth reading the whole thing.

[NOTE: You may have noticed that this post doesn't have a lot of original content (i.e. it's link spam).  This is because this post is one component of an experiment I'm conducting.  I wanted to submit the original post to Hacker News, but HN requires stories to be submitted with their original headlines.  The original headline for this story was, "The War Nerd: Here’s everything you need to know about 'too extreme for Al Qaeda' I.S.I.S." which I predicted would not get a lot of traction on HN, and I wanted to draw particular attention to the idea that what is going on in the Middle East can be understood in terms of relatively simple principles analogous to the basic laws of physics.  So I'm submitting both this post and the original, with full disclosure, to see what happens.]

[UPDATE: It appears that both submissions are going to fall off the bottom of the HN New page without getting a single upvote.   5 AM may not have been the best time to do this experiment.]

Friday, September 12, 2014

Are parallel universes real?

Since I gave my Google Tech Talk on quantum mechanics nearly four years ago I get a steady stream of email from people asking questions about it.  There's one question I keep getting over and over which I thought I'd just try to answer once and for all so I could point people to this answer instead of improvising a new one from scratch every time.

Note that this blog post assumes that you have either watched the video or read the associated paper.  If you haven't, what follows will probably not make a lot of sense.

The question I keep getting is some variation on the following theme: What is the relation of the QIT/zero-worlds interpretation of QM to interpretation X, where X is usually many-worlds, but is sometimes relative state.  Riffing off this I'll get questions about the implications of QIT for time-travel, the relationship of QM to consciousness, and whether or not we might be able to influence the results of quantum measurements with our minds.

The short version of the answer is: QIT/zero-worlds is nothing more than a different way of looking at the math than what is usually presented in the popular press.  It is a way of looking at the math that makes sense to me (and apparently, based on the feedback I get, makes sense to a lot of other people as well).  But that is all it is.  There is no breakthrough here (except, perhaps, a pedagogical one).  It turns out that all this stuff was actually known as early as the 1930s.  Why Feynman was still saying that no one understood quantum mechanics in the 1960s I do not know.  It is certainly not true today.  But the point is that despite the somewhat sensational rhetoric ("You don't really exist; you are living in a simulation running on a quantum computer") nothing really changes as a result of QIT except your perspective.  You are still every bit as real (or not) as you were before.  Time travel, ESP, and telekinesis are still every bit as impossible as they were before.

The other short version of the answer is that many-worlds/relative-state/whatever are all equally valid ways of looking at QM.  The only one that isn't equally valid is Copenhagen.  To be sure, Copenhagen is a reasonable approximation to the truth for many practical purposes, just as Newtonian mechanics is a reasonable approximation to the truth (which is, to the best of our current knowledge, general relativity) for many practical purposes.  But Copenhagen is conceptually wrong, just as Newtonian mechanics is conceptually wrong.  There is no "force of gravity" and the wave function never collapses.  The challenge is to explain why it appears to do so.  That is what QIT does (IMO).

Let's take a moment to review the problem that QIT (and other interpretations of QM) purport to solve: QM is one of the two most successful scientific theories ever (the other being GR).  No experiment has ever disagreed with a prediction made by QM.  However, the mathematics of QM seem to be fundamentally at odds with the apparent nature of reality.  The Shroedinger equation is continuous, deterministic, and time-reversible.  Moreover, it describes a world where objects can exist in superpositions of states, a phenomenon which can be experimentally demonstrated through interference experiments.  By way of contrast, the world appears to consist of material objects which at all times exist in some particular state and never in a superposition.  Moreover, the process of making a measurement appears to be discontinuous, non-reversible, and also involves some fundamental randomness which is nowhere to be found in the Shroedinger equation.  The apparent contradiction between the theory and the manifest nature of reality has historically been called the "measurement problem."

QIT solves the measurement problem by observing that you can describe measurement as a purely quantum process.  When you do this, the following facts emerge (and this is what the Google tech talk and associated paper are about):

1.  Measurement and entanglement are the same physical phenomenon.  Measurement is nothing more than the mutual entanglement of a large collection of particles (or, to be strictly correct, of systems that manifest themselves as particles under certain circumstances).

2.  Once two particles are entangled, it is not possible to "undo" that entanglement except by bringing the two particles physically together.  If there were any other way to "undo" an entanglement, then it would be possible to transmit information faster than light.

3.  The apparent randomness that results from a quantum measurement is just that: apparent.  In actual fact, the entropy of a system that has undergone a quantum measurement does not change.  The reason that there seems to be randomness is that when you draw a line between the particle being measured and the measurement apparatus, you end up with positive entropy (i.e. randomness) in the measurement apparatus and corresponding negative entropy in the particle being measured (which is possible because the state of the particle is a complex number).

4.  The reason that two measurements made on the same physical quantity produce the same result is not that the measurements are a faithful reflection of some underlying physical (or metaphysical) "element of reality" as Einstein put it.  Instead, if you look at the quantum mechanical description of two separate measurements on the same system what you end up with is a mathematical description that looks exactly the same as two classical systems in classical correlation with each other, but that says nothing about the actual state of the system being measured (except that it is now entangled with the measurement apparatus).

5.  The apparent non-reversibility of a measurement is likewise not fundamental, but merely practical.  Reversing a measurement is possible in principle, but to reverse a measurement, you have to reverse all of the entanglements that produced that measurement to begin with.  Reversing even a single entanglement is extremely difficult.  Reversing a macroscopic number of them (and you really do have to get them all, every single last one), while possible in principle, is not possible in practice.

In other words, there is no measurement problem.  All of the apparent contradictions between the mathematics of QM (continuous, deterministic, time-reversible) and measurement (discontinuous, random, non-reversible) can be understood purely in terms of quantum mechanics itself.  Furthermore, all of this (except possibly the bit about negative entropies) was known in the 1930s.  So why has QM been considered so intractably mysterious for so long?  Indeed, why is QM *still* considered by many to be intractably mysterious?

I don't really know, but I suspect it's because people don't want to accept what the math is telling them.  The math says, essentially, that you don't really exist (or, if you prefer, your existence is not unique -- it turns out these are two equivalent ways of saying the same somewhat ineffable thing).  This is not the first time this has happened.  The exact same kind of conceptual stumbling block delayed the discovery of relativity for decades.  The fact that Maxwell's equations predicted the existence of electromagnetic waves moving at a fixed velocity c was known in the mid-1800s.  But no one took this seriously until 1905, because it was just obvious that time and space are absolute and so there just had to be some fixed medium through which electromagnetic waves propagated and relative to which the predicted speed c was to be measured.

The similarly obvious (but nonetheless false) assumption that everyone gets hung up on today is that the universe is, in point of metaphysical fact, what it appears to be: the whole of creation, populated by material objects that exist in particular places at particular times.  The answer to the puzzle: how can such a universe arise from quantum mechanics is, quite simply: it doesn't.  It appears to, but this is an illusion.  To be sure, the illusion is quite compelling, but it is false.  It is every bit as false as the illusion that space and time are two distinct things (which can also, it should be reiterated, be quite compelling).

It is worth pointing out that the fact that the underlying truth is very different from what we naively perceive it to be is evident long before you get to quantum mechanics.  You think that the chair you are sitting on is a solid object, but in fact it is mostly (>>99%) empty space.  The reason is appears to be solid is that the electrons in the outer shells of the atoms that make up the chair repel the electrons in the outer shells of the atoms that make up your body (or your pants).  So even in a pre-Shroedinger world, things are very different than they appear.

OK, so atoms aren't solid, but they are still (in a post-Rutherford but pre-Shroedinger world) classical.  They exist at definite places at definite times.  It makes sense to distinguish this particular hydrogen atom that is part of a water molecule in your little finger from that hydrogen atom which is undergoing nuclear fusion in the core of the sun.  It is obvious that atoms are classical material objects.  We can even take pictures of them and move them around nowadays.  The evidence that atoms are classical is overwhelming.  How could it not be true?

Well, it's not true.  Not only is it commonplace nowadays to take pictures of atoms and move them around, it is also commonplace to do interference experiments with them.  And not just atoms, but enormous molecules have been observed to interfere.  And yet, it is obvious (and at this point that phrase should be ringing alarm bells in your head) that somewhere between a buckeyball and you there must be a line where the world really does become classical because it is obvious that you are classical.

Sorry to be the one to break this to you, but you're not.  The evidence that you are classical is indeed overwhelming, just as the evidence that space and time are absolute is overwhelming.  But in fact neither is true.  The reason you can take a picture of an atom is not that the atom is really there, but because in the process of taking the picture your camera becomes entangled with the atom.  Then, when you look at the picture, you become entangled with the camera.  The reason you think that there's an atom there is because you are a large system of mutually entangled particles, hence quantum mechanics predicts that any particular part of you will behave as if it were a classical system in classical correlation with every other part of you.  The net result is a system where every piece of it agrees that there is (or is not) an atom there.  And asking your fellow humans to corroborate your intuitions doesn't help, because they too are large systems of mutually entangled particles, and as soon as they look at the same picture you have looked at, they too become entangled with it and with you and with the original atom, and so every part of that system (you plus your collaborators) will agree that there was an atom there (or not).

So is the atom "really" there?

The problem with this question is that it seems like the answer should be either "yes" or "no", but this too is false.  The nature of this question is more like this one:

Was Darth Vader (or, if you prefer, Anakin Skywalker) "really" Luke's father?

One the one hand, it seems that the answer should be "yes" because, in the Star Wars universe, Anakin/Vader was Luke's father.  But, of course, the Star Wars universe is fictional, so what does it mean for a fictional character to "really" have any particular attribute?

The answer, IMO, is to simply observe that fictional characters like Luke Skywalker and Harry Potter are in a different "ontological category" from (classically) real things like George Lucas or J.K. Rowling.  Well, the quantum wave function is also in a different ontological category than classical reality.  Fiction "emerges" from (classical) reality in much the same way that classical reality "emerges" from the wave function.  (The reason I hedge with "much the same way" is that there is one important difference: fiction and classical reality can both be described as classical computational processes, i.e. the math involves only real numbers, whereas the quantum wave function can only be described with complex numbers.  So the process by which classical reality emerges from the wave function is mathematically different (but conceptually similar) from the process by which fiction emerges from classical reality.)

So is the atom "really" there?  Well, to you it is.  It is every bit as real as you yourself are, and for the exact same reason: because the atom is part of the system of mutually entangled particles of which you are a part.  (This is sometimes called the "relative state" interpretation of QM.)

But let's take a different example.  Instead of asking whether the atom is really "there" let us ask instead if one of its electrons is "really" spin-up or spin-down (or, equivalently, if some photon it emits is "really" polarized vertically or horizontally).  You measure it, and the result is spin-up.  Your friend measures the same electron and agrees, yep, it's spin-up.  So you and your friend have become mutually entangled with this electron and hence are behaving just like a pair of classically correlated classical systems, just as QM predicts.

But, while QM predicts that you will be classically correlated, it does NOT (and cannot) predict what the outcome of your measurements will actually be.  That can only be done probabilistically, which seems at odds with QM (which is, if you will recall, purely deterministic).  To understand this we have to dig a little deeper into the math.  I've hinted at this before when I said that in order to extract a description of the classical world from the wave function you have to "trace over certain degrees of freedom".  That is just a fancy way of saying, "discard some of the information about the system."  Consider the full QM description of a particle that has been measured.  Part of that description is the state of the particle, and the other part is the description of the measurement apparatus.  To extract the state of the measurement apparatus you "trace over" (i.e. discard) the parts of the description that describe the state of the particle being measured.  What you are left with is not one classical world, but two: one in which the measurement apparatus says spin-up, the other in which it says spin-down.  But (and this is the crucial point) in neither of these descriptions is the spin of the particle actually spin-up or spin-down.  It can't be.  There is no description of the state of the particle being measured, because we had to throw it out in order to extract a description of (something that looks like) a classical universe, and that actually turns out to be a description of two classical universes.  That is where the "multiple worlds" interpretation comes from.

So do these universes "really exist"?  Again, in my opinion that's like asking whether Darth Vader is "really" Luke's father.  Classical universes are what you get when you take the quantum wave function and throw out parts of it.  That is the mathematical fact.  You can interpret this mathematical fact however you choose, with one exception: you cannot reasonably conclude that the classical universe that you live in is "all there is" because a complete description of the (classical) state of the universe is only, and can only ever be, a partial description of the underlying quantum state.

So what about all those other universes?  Are they real?  Well, from the perspective of the quantum wave function, yes, they are.  A classical universe is just a "slice" of the wave function (i.e. the whole wave function with parts of it discarded) and the wave function doesn't care which way you slice.  It's rather like if someone wrote an alternate Star Wars universe where Darth Vader was not Luke's father.  The existence of such an alternate Star Wars universe would have no bearing on whether Darth Vader was Luke's father in the original Star Wars universe (the answer there would remain "yes") nor would it have any bearing on whether Darth Vader was Luke's father in the "real" universe in which both Star Wars universes were embedded (as fiction): the answer there would remain that the question is meaningless because mixing ontological categories makes no sense.

David Deutsch, for whom I have the utmost respect (I think he's actually one of the best popularizers of science ever) is a fierce proponent of the proposition that all classical universes are equally real.  I respectfully disagree with him.  It is true that they are all equally real from the perspective of the wave function.  But I don't have the perspective of the wave function, and neither do you.  You and I live in this universe, and so to us, this universe is more real than any of the other myriad universes that emerge from the wave function.  There may be a transporter in the Star Trek universe, but that doesn't help Luke Skywalker escape from Emperor Palpatine because Luke can only take advantage of (and hence only cares about) what exists in his universe.

What about the possibility of communicating between universes?  Wouldn't that be cool?  If those universes are "as real as we are", shouldn't that be possible?  Well, unfortunately, no, it's not.  The way in which classical universes emerge from the wave function makes communication between them impossible.  You can prove this mathematically, just as you can prove that quantum entanglement can't be used to send information faster than light.  This is another reason I believe that parallel universes can safely be regarded as less real than our own universe, at least by us.  But reasonable people can (and do) disagree.

There's a lot more to say about this topic, but this post has already become longer than I intended it to be.  I'll write more if there's interest, but I want to leave you with a parting thought (well, more of an exercise actually): remember that I said that measurements were in principle reversible.  Imagine that we could actually carry out this program of undoing the myriad entanglements that constitute your making a particular observation.  What would be the subjective sensation, i.e. what would it "feel like" if this were done to you?

Wednesday, August 20, 2014

The many elephants in the room in Ferguson, Missouri

As long as I'm pointing out the obvious, I figure I should point out a few of the proverbial elephants in the living room in Ferguson, Missouri: the town is 70% black, but the government is overwhelmingly white.  There are only two possible reasons for this: either blacks think that having their town run by whites is just hunky dory, or blacks in Fergusson don't vote.  Unsurprisingly, the latter turns out to be the case.
According to a Washington Post analysis, an estimated 6% of blacks and 17% of whites turned out for the 2013 municipal elections in the township
I was shocked by these numbers.  It's not just that blacks don't vote, nobody votes in Ferguson!  Let's do the math: Ferguson has about 21,000 residents.  70% are black, 30% white.  So 21,000 x 0.7 x 0.06 = 880 black people voted, and 21,000 x 0.3 x 0.17 = 1070 white people voted.

As the mechanic who opened the hood of the non-function car only to find that the engine was gone said, "Well, there's yer problem right there."  It would only take an additional 250 black voters showing up to completely reverse the power dynamic in Ferguson.  That (and remember, this post is about pointing out the obvious) is far fewer than the number showing up to protest in the streets.

If there is a silver lining to Michael Brown's tragic death it is that Ferguson's black community might be finally driven out of their complacency.  There are renewed efforts to register black voters there.  And also unsurprisingly (pointing out the obvious again), Republicans are not happy about it:
In an interview with Breitbart News, Missouri RNC executive director Matt Wills expressed outrage about the reports [of efforts to register black voters].
“If that’s not fanning the political flames, I don’t know what is,” Wills said, “I think it’s not only disgusting but completely inappropriate.”
So black people registering to vote is "disgusting and inappropriate" according to the Republicans.  I'll say this for Matt Wills: at least he's willing to stand up for what he believes.  But as long as I'm pointing out the obvious, I will once again celebrate the fact that we live in a great country, where everyone has a right to express their views, no matter how repugnant.

Finally, no discussion of Ferguson and repugnant views would be complete without giving a shout-out to Professor Sunil Dutta, an ex-police officer who opined in the Washington Post that the best strategy for not getting shot dead by a police officer is to unquestioning obsequiousness.  Pointing out the obvious is starting the get a little old, so I'll leave it up to the fine folks at Reason.
If you have the attitude that you are owed deference and instant obedience by the people around you, and that you are justified in using violence against them if they don't comply, we already have a problem. That's especially true if official institutions back you up, which they do. 
If you really think that everybody else should "just do what I tell you," you're wearing the wrong uniform in the wrong country. And if you really can't function with some give and take—a few nasty names, a little argument—of the sort that people in all sorts of jobs put up with every damned day, do us all a favor: quit. 
The law enforcement problem in this country goes well beyond boys with toys. It's much deeper, and needs to be torn out by the roots.

This is what real religious persecution looks like, part 2

Religious persecution does not look like this.  It looks like this:
Saudi Arabia’s Commission for the Promotion of Virtue and Prevention of Vice has asked the interior ministry to arrest several people for apostasy and atheism. 
The commission did not divulge the number of people whose arrest it requested, but it said that they insulted God and Prophet Mohammad (PBUH).
 And this:
In 13 countries around the world, all of them Muslim, people who openly espouse atheism or reject the official state religion of Islam face execution under the law, according to a detailed study issued on Tuesday. 
And beyond the Islamic nations, even some of the West's apparently most democratic governments at best discriminate against citizens who have no belief in a god and at worst can jail them for offenses dubbed blasphemy, it said.
And this:
Israeli police on Sunday blocked more than 200 far-right Israeli protesters from rushing guests at a wedding of a Jewish woman and Muslim man as they shouted "death to the Arabs" in a sign of tensions stoked by the Gaza war.
(The persecution in this case, of course, being perpetrated by the mob, not the police.)

There really is very little sport in finding examples of religious persecution around the world, but not in the U.S.  What you will find in the U.S. is a fair number of bigots whining about the decline of bigotry in polite society.  You'll also find people who think the earth is flat.  Some people are impervious to reason.

Sunday, August 10, 2014

What's wrong with this picture?

Here's a hint: Dick Durbin is not a Republican.

This is what real religious persecution looks like

Just in case your persecute-o-meter needs calibration:
National spokesman for Iraqi Christians and Chaldean-American businessman Mark Arabo said the "evil" being carried out by ISIS militants in Iraq now includes shocking beheadings of children...
I try to temper my criticism of religious people with empathy for the reason I believe they adhere to their faiths, but I feel driven to say that in the cold light of true religious persecution, the baseless whining of some American Christians really starts to look pretty reprehensible.

Are Christians persecuted in the United States?

The answer to the titular question is so clearly "no" that I would normally not dignify it with a response.  But commenter Publius, who otherwise seems to be reasonable and rational, presented some data to support the proposition that "finding Christian harassment in the past few years is like fishing with dynamite."  So I decided to take the time to investigate.  After all, it is important to keep an open mind.  You never know when one of your prejudices might turn out to be wrong.

Publius cites five primary examples, six secondary examples, and three examples that he characterizes as "vignettes".  I looked at every one of these and, unsurprisingly, they do not support the conclusion.  Of Publius's fourteen examples, only one is even a legitimate example of harassment of any sort.  That is this one:

Two tennagers assaulted by UCSB professor and suffer grand theft
Remember the University of California, Santa Barbara feminist studies professor who forcibly stole a graphic anti-abortion sign from two abortion protesters, then scratched and appeared to push one of the protesters (a 16-year-old girl), then destroyed the sign? 
She pleaded no contest to misdemeanor charges of grand theft, vandalism and battery on Thursday.
This is clearly a case of harassment (as even the perpetrator has now tacitly admitted).  But it is not a case of harassment of Christians.  We don't even know for certain that the victims were Christians, at least not from the account that Publius cites.  The word "Christian" does not even appear in that story.  It might be a good bet that they were Christians (because opponents of reproductive freedom often are) but we don't know that,  and it doesn't matter anyway.  Even if they were Christians it is clear that they were attacked not because of their religious beliefs but because of the political views they were espousing (not that this makes the attack any less reprehensible).  As you will see, this will prove to be a common theme.

The only other incident that involves violence is this one:

Hate crime: gay activists brutally beat christians in America
As revealed in the disturbing video, two Christian street preachers stood near a gay pride march, one holding a large sign and the other one clutching a Bible. 
The sign did not make any targeted, inflammatory statements against any particular group.
But several of the marchers did not care.
A heavy-set man and a woman broke off from the march to confront the preachers. The preacher in the “Trust Jesus” t-shirt tried to block the initial shoving with his Bible. 
Both preachers attempted to retreat from conflict.
A short man knocked down the preacher holding the sign, taking it away from him as the heavy-set man sucker punched the preacher in the head. 
The short man showed no mercy as he kicked the now-down preacher in the ribs.
This sounds pretty damning, and the violence is, again, reprehensible.  However, if you watch the video you will see a number of salient points that are not mentioned in the written account:

1.  The incident happened at a gay pride rally.

2.  The preachers were repeatedly warned verbally and in no uncertain terms that their presence was not welcome, and were advised, again in no uncertain terms, that they should leave.

3.  The inciting incident was not an attack on the preachers themselves, but the theft of one of their signs.  You can watch the video and judge for yourself who was attacking who, but the fact is that for most of the fracas, the preacher being "attacked" is on top of the putative "attacker."

So again, even if one grants that the preachers were attacked, they were not attacked because they were Christians, they were attacked because they were behaving like assholes.  Preaching that homosexuality is a sin at a gay pride rally is like walking into a church and preaching against God.  It's just rude.  Of course rudeness does not merit violence, but it does forfeit you the moral high ground.

Two down, twelve to go.  This is going to be a long slog, but I really want to definitively debunk this idea that Christians are the victims.

Brendan Eich resigns as CEO of Mozilla
The resignation of Mozilla's CEO amid outrage that he supported an anti-gay marriage campaign is prompting concerns about how Silicon Valley's strongly liberal culture might quash the very openness that is at the region's foundation. 
Mozilla co-founder Brendan Eich stepped down Thursday as CEO, just days after his appointment. He left the nonprofit maker of the Firefox browser after furious attacks, largely on Twitter, over his $1,000 contribution to support of a now-overturned 2008 gay-marriage ban in California.
As with the case of the UCSB professor's victims, we have no evidence that Brendan Eich is a Christian.  Just as it is possible for a non-Christian to oppose abortion rights, it is also possible for a non-Christian to oppose marriage equality.  I myself wrote some harsh criticism of Brendan Eich and I have no idea if he's a Christian or not.  What I do know (because Brendan's actions provide conclusive evidence) is that he is an unrepentant bigot.  Personally, I have no problem with bigots being harassed for their bigotry.  I am not a moral relativist.  Bigotry is evil because it retards the advancement of ideas.  But that is another discussion.

Protests against Catholic and Morman churches for California Prop. 8 support
Protests against Proposition 8 supporters in California took place starting in November 2008. These included prominent protests against the Roman Catholic church and The Church of Jesus Christ of Latter-day Saints (LDS Church), which collaboratively campaigned in favor of California's Proposition 8 through volunteer and financial support for the measure.[1] The proposition was a voter referendum that amended the state constitution to recognize marriage only as being between one man and one woman, thus banning same-sex marriage, which was legal in the state following a May 2008 California Supreme Court case.
Same story, except that these protests are not harassment of any sort.  They are entirely legitimate political responses to political action.  They are a response to bigots who made themselves fair game by initiating political action to deprive other people of their rights.  That these particular bigots happen to be Mormon has nothing to do with the protests (except insofar as their Mormonism almost certainly motivated their bigotry).

Chick-fil-A faces protests after comments by COO Dan Cathy
American fast-food chain Chick-fil-A was the focus of controversy following a series of public comments made in June 2012 by chief operating officer Dan Cathy opposing same-sex marriage. This followed reports that Chick-fil-A's charitable endeavor, the S. Truett Cathy-family-operated WinShape Foundation, had made millions in donations to political organizations which oppose LGBT rights. LGBT rights activists called for protests and boycotts of the chain, while counter-protestors rallied in support by eating at the restaurants. National political figures both for and against the actions spoke out and some business partners severed ties with the chain. 
Chick-fil-A released a statement in July 2012 stating, "Going forward, our intent is to leave the policy debate over same-sex marriage to the government and political arena."
Are you beginning to notice a pattern here?  Do I even need to explain this one?  Again, these protests were political, peaceful, and their motives had nothing to do with the subject of their protests being Christian and everything to do with their being politically active bigots.

Military priests face arrest for celebrating mass
According the Archdiocese for Military Services, GS and contract priests (who are paid by the federal government as independent contractors in places where there aren’t enough active-duty priests to meet the needs of Catholics in military service) are being forbidden from celebrating Mass, even on a volunteer basis. 
If they violate this restriction, they face possible arrest. FOR CELEBRATING MASS.
OK, this sounds more promising.  Being arrested for celebrating mass certainly sounds like a flagrant violation of the First Amendment.  But again, there is a salient fact that is not evident from these excerpts: this incident occurred during the government shutdown of October 2013.  In fact, Publius edited the headline to obscure this fact.  The original headline was "MILITARY PRIESTS FACE ARREST FOR CELEBRATING MASS IN DEFIANCE OF SHUTDOWN" (caps in original).  So again, the priests were not facing arrest because they were Christian, they were facing arrest because they were breaking the law.  During the shutdown (which, again, it is worth noting was precipitated by the intransigence of Congressional Republicans), many contractors were furloughed and hence barred from government facilities.  But were Christians specifically singled out?  Publius's next example is closely related:

The Obama administration is continuing to prohibit approximately 50 Catholic priests from saying Mass and administering other sacraments at U.S. military facilities around the world, according to the Roman Catholic Archdiocese for the Military Services. 
Father Ray Leonard, who is one of these priests, and who serves as the Catholic chaplain at Navel Submarine Base Kings Bay in Georgia, filed suit Monday against the Department of Defense, Defense Secretary Chuck Hagel, the Department of the Navy and Navy Secretary Ray Mabus. His suit—joined by Navy veteran Fred Naylor, who is a member of the Catholic congregation at Kings Bay--alleges that the administration is violating his and his congregation’s First Amendment rights to the free exercise of religion, the freedom of speech and the freedom of assembly. 
DOD has been prohibiting Father Leonard and the other Catholic priests from administering the sacraments and providing other services to their congregations even though two weeks ago Congress passed, and President Barack Obama signed, a law that instructed DOD to maintain on the job and keep paying contract employees who were supporting the troops. 
DOD took this action because Hagel determined--after consulting with Attorney General Eric Holder's Justice Department--that civilian Catholic priests, working under contract as chaplains, did not, among other things, “contribute to the morale” and “well-being” of service personnel. 
"The Department of Defense consulted closely with the Department of Justice, which expressed its view that the law does not permit a blanket recall of all civilians," Hagel said in an Oct. 5 memorandum. "Under our current reading of the law, the standard of 'support to members of the Armed Forces' requires a focus on those employees whose responsibilities contribute to the morale, well-being, capabilities, and readiness of covered military members during the lapse of appropriations." 
Among the specific examples Hagel provided of civilian contractors whom he believes meet this standard are those working in secular "Family Support Programs and Activities," "Behavorial Health and Suicide Prevention Programs" and "Health Care Activities and Providers"--but not priests.
Wow, that really does sound bad.  But if you actually look at the Oct. 5 memorandum you will find that things are not exactly as they are portrayed in the CNS News account.  For one thing, the words "Catholic", "Christian" and "priest" do not appear in that memo.  What is really going on here, as the memo makes clear, is that Congress shut down the government and left it up to the executive branch in general, and the DoD in particular in this case, to figure out how to handle the resulting mess.  The DoD prioritized what it considered to be essential services (like supply chain management -- i.e. providing soldiers with food) and religious services didn't make the cut.  Even if you allow the English language to be sufficiently mangled as to allow the decision to prioritize food over organized religious services to be characterized as "harassment", this incident is still in no way harassment of Christians.  All religious services were suspended, not just Christian ones.  It's just that the Christians were the only ones who whined about it.

US Army defines Christian ministry as domestic hate group"
Several dozen U.S. Army active duty and reserve troops were told last week that the American Family Association, a well-respected Christian ministry, should be classified as a domestic hate group because the group advocates for traditional family values.
You should be able to guess that this account is stilted merely by the fact that the source is Fox News.  First, it was not "The U.S. Army", it was a single instructor at a single briefing.  And second, it is in fact defensible to call the American Family Association a hate group because they do in fact promulgate hateful ideas about gays.

Florida Teacher Suspended for Anti-Gay Marriage Posts on Personal Facebook Page
A former “Teacher of the Year” in Mount Dora, Fla. has been suspended and could lose his job after he voiced his objection to gay marriage on his personal Facebook page. 
Jerry Buell, a veteran American history teacher at Mount Dora High School, was removed from his teaching duties this week as school officials in Lake County investigate allegations that what he posted was biased towards homosexuals.
Yes, I know.  It's starting to get a little painful, isn't it?  Like Brendan Eich, this teacher was not fired for being a Christian, this teacher was fired for being a bigot.

We're nearly done.  Only one more "vignette" to go:

U.S. Airman punished for his faith
The shocking stories of religious hostility in our nation’s military continue, and now, Liberty Institute represents Senior Master Sergeant Phillip Monk, a 19-year veteran of the U.S. Air Force who was relieved of his duties because of his faith and moral convictions. 
Senior Master Sergeant Monk, who served as a First Sergeant at Lackland Air Force Base in San Antonio, recently returned from deployment and found he had a new commander who was an open lesbian. 
“In one of our first meetings, she was talking about her promotion and she mentioned something about a benediction,” Monk told Fox News. “She said she wanted a chaplain but objected to one particular chaplain that she called a ‘bigot’ because he preached that homosexuality is a sin.” 
“She then said, ‘I don’t know what kind of people actually believe that kind of crap,’” Monk continued. “I knew I was going to have a rough time in this unit and I would have to be very careful about what I said.” 
Issues arose when Monk was asked to advise his commander on a disciplinary matter involving an Air Force instructor who was accused of making objectionable comments about gay marriage. After a thorough investigation, Monk determined the instructor meant no harm by his comments, and suggested that his commander could use the incident as a way to teach about tolerance and diversity. 
Monk, a devout evangelical Christian, says he was told that he wasn’t on the same page as the commander, and that if he didn’t get on the same page, they would find another place for him to work. 
Later, the commander ordered Monk to answer the question of whether people who object to gay marriage are discriminating. Monk responded that he could not answer the way his commander wanted and feared an honest response would put him in legal trouble. 
At that point, Monk was relieved of his duties.
It's hard to sort out exactly what happened in this case, but whatever it was it had nothing to do with Christianity and everything to do with homophobia.  This is not to say that Monk's dismissal was appropriate.  People have a Constitutional right to be hold bigoted views, and a case might be made that homophobic bigots are being subject to unfair harassment.  But the evidence for harassment targeted at Christians is zero.  Zip.  Nada.

To see what systematic discrimination against a worldview looks like you have to look at atheism, because atheists are subject to systematic discrimination (which occasionally rises to the level of harassment) in the U.S.  For example, "Humanist" was not recognized as a religious affiliation by the military before April of this year.  As recently as June of last year, a proposal to fund Humanist chaplains in the military failed to pass.  Can you imagine the uproar if Catholics were specifically excluded from the chaplaincy?  And yet that is exactly the situation that non-theists in the military face.  Atheists are the last minority towards which systematic societal discrimination is still considered acceptable.
Discrimination against atheists in the United States occurs in legal, personal, social, and professional contexts. Some American atheists compare their situation to the discrimination faced by ethnic minorities, LGBT communities, and women.[42][43][44][45] "Americans still feel it's acceptable to discriminate against atheists in ways considered beyond the pale for other groups," asserted Fred Edwords of the American Humanist Association.[46] However, other atheists reject these comparisons, arguing that while atheists may face disapproval they have not faced significant oppression or discrimination.[47][48] 
In the United States, seven state constitutions include religious tests that would effectively prevent atheists from holding public office, and in some cases being a juror/witness... 
Respondents to a survey were less likely to support a kidney transplant for hypothetical atheists and agnostics needing it, than for Christian patients with similar medical needs.[59] 
Few politicians have been willing to identify as non-theists, since such revelations have been considered "political suicide".[64][65] In a landmark move, California Representative Pete Stark came out in 2007 as the first openly nontheistic member of Congress.[46] In 2009, City Councilman Cecil Bothwell of Asheville, North Carolina was called "unworthy of his seat" because of his open atheism.[66] Several polls have shown that about 50 percent of Americans would not vote for a qualified atheist for president.[67][68] A 2006 study found that 40% of respondents characterized atheists as a group that did "not at all agree with my vision of American society", and that 48% would not want their child to marry an atheist. In both studies, percentages of disapproval of atheists were above those for Muslims, African-Americans and homosexuals.[69] Many of the respondents associated atheism with immorality, including criminal behaviour, extreme materialism, and elitism.[70] Atheists and atheist organizations have alleged discrimination against atheists in the military,[71][72][73][74][75][76] and recently, with the development of the Army's Comprehensive Soldier Fitness program, atheists have alleged institutionalized discrimination.[77][78] In several child custody court rulings, atheist parents have been discriminated against, either directly or indirectly. As child custody laws in the United States are often based on the "best interests of the child" principle, they leave family court judges ample room to consider a parent’s ideology when settling a custody case. Atheism, lack of religious observation and regular church attendance, and the inability to prove one's willingness and capacity to attend to religion with his children, have been used to deny custody to non-religious parents.[79][80]
The constitutions of ... seven US states ban atheists from holding public office.
And here we come to the real nub of the matter.  Not only is it false that Christians are systematically discriminated against, in fact the exact opposite is true.  Christians are not the discriminatees, they are the discriminators.  They have in fact become so accustomed to their position of power and hegemony in American society that they perceive that power and hegemony as a basic right, as the natural order of things.

Well, it isn't.  Notwithstanding that the vast majority of Americans self-identify as Christians,  the United States is not a Christian nation.  It never was, and God willing it never will be.  It is a secular nation, areligious (but obviously not irreligious).  It welcomes Christians and non-Christians of all stripes.  It welcomes Catholics and Krishnas, Baptists and Buddhists, Methodists and Muslims, believers and non-believers.

What it does not welcome so much is intolerance.  If you believe that God wants you to impose (your view of) His will on others, then you do indeed have a problem, because the price of being free to worship as you see fit is to leave others free to do the same (or not) as they see fit.  So if you really feel persecuted here because you can't stand letting other people enjoy the same freedoms you possess, you might want to consider moving to, say, Cameroon.  We won't stop you.