Timey-wimey light

I don't always need to understand things to appreciate them.

In fact, there's a part of me that likes having my mind blown.  I find it reassuring that the universe is way bigger and more complex than I am, and the fact that I actually can parse a bit of it with my little tiny mind is astonishing and cool.  How could it possibly be surprising that there's so much more out there than the fragment of it I can comprehend?

This explains my love for twisty, complicated fiction, in which you're not handed all the answers and everything doesn't get wrapped up with a neat bow at the end.  It's why I thoroughly enjoyed the last season of Doctor Who, the six-part story arc called "Flux."  Apparently it pissed a lot of fans off because it had a quirky, complicated plot that left a bunch of loose ends, but I loved that.  (I'm also kind of in love with Jodie Whittaker's Thirteenth Doctor, but that's another matter.)

I don't feel like I need all the answers.  I'm not only fine with having to piece together what exactly happened to whom, but I'm okay that sometimes I don't know.  You just have to accept that even with all the information right there in front of you, it's still not enough to figure everything out.

Because, after all, that's how the universe itself is.

[Nota bene: Please don't @ me about how much you hated Flux, or how I'm crediting Doctor Who showrunner Chris Chibnall with way too much cleverness by comparing his work to the very nature of the universe.  For one thing, you're not going to change my mind.  For another, I can't be arsed to argue about a matter of taste.  Thanks.]

In any case, back to actual science.  That sense of reality being so weird and complicated that it's beyond my grasp is why I keep coming back to the topic of quantum physics.  It is so bizarrely counterintuitive that a lot of laypeople hear about it, scoff, and say, "Okay, that can't be real."  The problem with the scoffers is that although sometimes we're not even sure what the predictions of quantum mechanics mean, they are superbly accurate.  It's one of the most thoroughly tested scientific models in existence, and it has passed every test.  There are measurements made using the quantum model that have been demonstrated to align with the predictions to the tenth decimal place.

That's a level of accuracy you find almost nowhere else in science.

The reason all this wild stuff comes up is because of a pair of papers (both still in peer review) that claim to have demonstrated something damn near incomprehensible -- the researchers say they have successfully split a photon and then triggered half of it to move backwards in time.

One of the biggest mysteries in physics is the question of the "arrow of time," a conundrum about which I wrote in some detail earlier this year.  The gist of the problem -- and I refer you to the post I linked if you want more information -- is that the vast majority of the equations of physics are time-reversible.  They work equally well backwards and forwards.  A simple example is that if you drop a ball with zero initial velocity, it will reach a speed of 9.8 meters per second after one second; if you toss a ball upward with an initial velocity of 9.8 meters per second, after one second it will have decelerated to a velocity of zero.  If you had a film clip of the two trajectories, the first one would look exactly like the second one running backwards, and vice versa; the physics works the same forwards as in reverse.

The question, then, is why is this so different from our experience?  We remember the past and don't know the future.  The physicists tell us that time is reversible, but it sure as hell seems irreversible to us.  If you see a ball falling, you don't think, "Hey, you know, that could be a ball thrown upward with time running backwards."  (Well, I do sometimes, but most people don't.)  The whole thing bothered Einstein no end.  "The distinction between past, present, and future," he said, "is only an illusion, albeit a stubbornly persistent one."

This skew between our day-to-day experience and what the equations of physics describe is why the recent papers are so fascinating.  What the researchers did was to take a photon, split it, and allow the two halves to travel through a crystal.  During its travels, one half had its polarity reversed.  When the two pieces were recombined, it produced an interference pattern -- a pattern of light and dark stripes -- only possible, the physicists say, if the reversed-polarity photon had actually been traveling backwards in time as it traveled forwards in space.

The scientists write:

In the macroscopic world, time is intrinsically asymmetric, flowing in a specific direction, from past to future.  However, the same is not necessarily true for quantum systems, as some quantum processes produce valid quantum evolutions under time reversal.  Supposing that such processes can be probed in both time directions, we can also consider quantum processes probed in a coherent superposition of forwards and backwards time directions.  This yields a broader class of quantum processes than the ones considered so far in the literature, including those with indefinite causal order.  In this work, we demonstrate for the first time an operation belonging to this new class: the quantum time flip.

This takes wibbly-wobbly-timey-wimey to a whole new level.

Do I really understand what happened here on a technical level?  Hell no.  But whatever it is, it's cool.  It shows us that our intuition about how things work is wildly and fundamentally incomplete.  And I, for one, love that.  It's amazing that not only are there things out there in the universe that are bafflingly weird, we're actually making some inroads into figuring them out.

To quote the eminent physicist Richard Feynman, "I can live with doubt and uncertainty and not knowing.  I think it's much more interesting to live not knowing than to have answers which might be wrong.  I have approximate answers and possible beliefs and different degrees of certainty about different things, but I'm not absolutely sure about anything."

To which I can only say: precisely.  (Thanks to the wonderful Facebook pages Thinking is Power and Mensa Saskatchewan for throwing this quote my way -- if you're on Facebook, you should immediately follow them.  They post amazing stuff like this every day.)

I'm afraid I am, and will always be, a dilettante.  There are only a handful of subjects about which I feel any degree of confidence in my depth of comprehension.  But that's okay.  I make up for my lack of specialization by being eternally inquisitive, and honestly, I think that's more fun anyhow.

 Three hundreds years ago, we didn't know atoms existed.  It was only in the early twentieth century that we figured out their structure, and that they aren't the little solid unbreakable spheres we thought they were.  (That concept is still locked into the word "atom" -- it comes from a Greek word meaning "can't be cut.")  Since then, we've delved deeper and deeper into the weird world of the very small, and what we're finding boggles the mind.  My intuition is that if you think it's gotten as strange as it can get, you haven't seen nothin' yet.

I, for one, can't wait.

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Order of operations

I try not to write in Skeptophilia about topics I don't fully understand -- well, at least understand as fully as my brainpower and the available information allow.  But today I'm going to tell you about a recent paper in theoretical physics that blew my mind so completely that I had to write a post about it, even though saying "I don't completely comprehend this" is a serious understatement.

So here goes.  Just don't ask me to clarify further, because the most you'll get is the Canine Head-Tilt of Puzzlement.

The paper, which appeared last week in Nature Communications, is entitled "Bell's Theorem for Temporal Order," and was written by Magdalena Zych and Fabio Costa (of the University of Queensland), Igor Pikovski (of Harvard University), and Časlav Brukner (of the University of Vienna).  The issue the four physicists were looking at was the seeming paradox of the different way that time (specifically, temporal order) fits into general relativity and quantum theory.  In relativity, the flow of time depends on your relative speed and the distribution of mass near you; in general, the faster you're going, or the nearer you are to a massive object, the slower your clock runs.  Because reference frame is relative (thus the name of the entire theory), you don't notice this effect yourself -- to you, your clock runs just fine.  But to someone observing you at a distance, the flow of time in your frame of reference has become more sluggish.

Weird enough, but that's only the beginning.  To take the most familiar example, consider two astronauts in spacecraft zooming away from each other at a substantial fraction of the speed of light.  To astronaut A, his clock is running fine, and astronaut B's clock is slow (because he's moving away from A at a high speed).  But from B's perspective, it's A that's moving; so B thinks his own clock is accurate, and A's is the one that's running slow.

And it's not that one's right and the other is somehow being fooled.  Both of them are right -- because time is relative to your speed.

As an outcome of this (and germane to the paper I referenced), what this also means is that A and B can differ in what they perceive as the time order of two events.  Occurrences that appear simultaneous to one of the astronauts might appear sequential to the other.

With me so far?  Well, the problem that Zych et al. were investigating was that in quantum theory, there's no allowance for relativistic ordering of events.  Time's arrow is one-directional, and if event X followed Y in one reference frame, it would do so on all reference frames.

Well, that's what the physicists thought -- until this paper showed a theoretical framework that suggests otherwise.

Zych et al. proposed a thought experiment involving two spaceships, one of which is near a massive object (which, as I mentioned, warps spacetime in such a way as to slow down the passage of time).  They're engaged in a war game that requires them to fire their phasers simultaneously and immediately afterward start their engine so as to dodge the blast.  The problem is, the ship near the massive object will have a slower clock, and will not be able to fire quickly enough to escape being blasted by the other ship.

So far, weird but not that hard to understand.  What Zych et al. did was to ask a single question: what if the two ships were in a state of quantum superposition before they fired?

Superposition is one of the weirdest outcomes of quantum physics, but it's been demonstrated experimentally so many times that we have no choice but to accept that this is how the universe works.  The idea is that if a physical system could exist in two or more possible states, its actual state is an array of possibilities all existing at the same time until some measurement destroys the superposition and drops the system into one of the possible outcomes ("collapsing the wave function").  The most famous iteration of this is Schrödinger's Cat, who is both alive and dead until the box is opened.

In the case of the ships, the superposition results in quantum entanglement, where the entire system acts as a single entity (in a causal sense).  Here's how the result is described in a press release from the University of Vienna:

If a powerful agent could place a sufficiently massive object, say a planet, closer to one ship it would slow down its counting of time.  As a result, the ship farther away from the mass will fire too early for the first one to escape. 

The laws of quantum physics and gravity predict that by manipulating a quantum superposition state of the planet, the ships can end up in a superposition of either of them being destroyed...  The new work shows that the temporal order among events can exhibit superposition and entanglement – genuinely quantum features of particular importance for testing quantum theory against alternatives.

So each of the ships is in a state of both being destroyed and not being destroyed, from the standpoint of an outside observer -- until a measurement is made, which forces the system into one or the other outcome.

Note what this isn't saying; it's not implying that one of the ships was destroyed, and we simply don't know which yet.  It's implying that both ships are in an entangled state of being blasted to smithereens and not.

At the same time.

The authors write:

This entanglement enables accomplishing a task, violation of a Bell inequality, that is impossible under local classical temporal order; it means that temporal order cannot be described by any pre-defined local variables.  A classical notion of a causal structure is therefore untenable in any framework compatible with the basic principles of quantum mechanics and classical general relativity.

All of which leaves me sympathizing a great deal with Winnie-the Pooh.

So there you have it.  It turns out that the universe is a weird, weird place, where our common-sensical notions of how things work are often simply wrong.  Even though I'm far from an expert -- I run into the wall pretty fast when I try to read actual papers in physics, or (for that matter) in most scientific fields -- I find it fascinating to get a glimpse of the actual workings of the cosmos.

Even if it blows my tiny little mind.

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This week's Skeptophilia book recommendation is a must-read for anyone interested in astronomy -- Finding Our Place in the Universe by French astrophysicist Hélène Courtois.  Courtois gives us a thrilling tour of the universe on the largest scales, particularly Laniakea, the galactic supercluster to which the Milky Way belongs, and the vast and completely empty void between Laniakea and the next supercluster.  (These voids are so empty that if the Earth were at the middle of one, there would be no astronomical objects near enough or bright enough to see without a powerful telescope, and the night sky would be completely dark.)

Courtois's book is eye-opening and engaging, and (as it was just published this year) brings the reader up to date with the latest information from astronomy.  And it will give you new appreciation when you look up at night -- and realize how little of the universe you're actually seeing.

[Note: if you purchase this book from the image/link below, part of the proceeds goes to support Skeptophilia!]