Stretching time

You know, I'm beginning to think that every time I want to write a piece about cosmology or physics, I should just write "Einstein wins again" and call it good.

One of my favorite science vloggers, theoretical physicist Sabine Hossenfelder, gives a wry nod to this every time Einstein's name comes up in her videos -- which is frequently -- giving a little sigh and a shake of the head, and saying "Yeah, that guy again."

Maybe we should just stop arguing with him.  [Image is in the Public Domain]

You may recall that a couple of weeks ago I did a post about a possible paradigm shift in cosmology that could account for the mysterious "dark energy," a property of spacetime that is causing the apparent runaway expansion of the universe.  While acknowledging that finding solid evidence for the contention is currently beyond our technical capabilities, I pointed out that it simultaneously does away with two of the most perplexing and persistent mysteries of physics -- dark energy, and the mismatch between the theoretical and experimentally-determined values of the cosmological constant.  (Calling it a "mismatch" is as ridiculous an understatement as you could get; the difference is about 120 degrees of magnitude, meaning the two values are off by a factor of 1 followed by 120 zeroes).

But this week a new study out of the University of Sydney has shown that another of Einstein's relativistic predictions about an expanding universe has been experimentally verified, so maybe -- to paraphrase Mark Twain -- rumors of the death of dark energy were great exaggerations.  A bizarre feature of the Theory of Relativity is time dilation, the fact that from the perspective of a stationary observer, the clock for a moving individual would appear to run more slowly.  This gives rise to the counterintuitive twin paradox, which I first ran into on Carl Sagan's Cosmos when I was in college.  If one of a pair of twins were to take off on a spaceship and travel for a year near the speed of light, then return to his starting point, he'd find that his twin would have aged greatly, while he only aged by a year.  To the traveler, his clocks seemed to run normally; but his stay-at-home brother would have experienced time running much faster.

As an aside -- this is the idea behind my favorite song by Queen, the poignant and heartbreaking "'39," the lyrics for which were penned by the band's lead guitarist, astrophysicist Brian May.  Give it a listen, and -- if you're like me -- have tissues handy.

In any case, the recent research looks at a weird feature of the effects of relativity on time.  The prediction is that the expansion of the universe should affect all the dimensions of spacetime -- and therefore, in the early universe, time should (from our perspective) seem to have been running more slowly.

And that's exactly what they found.  (Recall that when you're looking outward in space, you're looking backward in time.)  The trick was finding a "standard clock" -- some phenomenon whose rate is steady, predictable, and well-understood.  They used the fluctuations in emissions from quasars -- extremely distant, massive, and luminous proto-galaxies -- and found that, exactly as relativity predicts, the farther away they are (i.e. the further back in time you're looking), the more slowly these "standard clocks" are running.  The most distant ones are experiencing a flow of time that (from our perspective) is five times slower than our clocks run now.

"[E]arlier studies led people to question whether quasars are truly cosmological objects, or even if the idea of expanding space is correct," said study co-author Geraint Lewis.  "With these new data and analysis, however, we’ve been able to find the elusive tick of the quasars and they behave just as Einstein’s relativity predicts."

The bizarre thing, though, is the "from our perspective" part; just like the traveling twin, anyone back then would have thought their clocks were running just fine.  It's only when you compare different reference frames that things start getting odd.  So it's not that "our clocks are right and theirs were slow;" both of us, from our own vantage points, think time is running as usual.  Neither reference frame is right or wrong.  The passage of time is relative to your velocity with respect to another frame.

Apparently it's also relative to what the fabric of spacetime around you is doing.

I'm not well-versed enough in the intricacies of physics to know if this really is a death blow to the paradigm-shifting proposal of a flat, static universe I wrote about a couple of weeks ago, but at least to my layperson's understanding, it sure seems like it would be problematic.  So as far as the nature of dark energy and the problem of the cosmological constant mismatch, it's back to the drawing board.

Einstein wins again.

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Zoom!

Today I'm going to continue on my exploration of weird physics, which has happened not only because I find it fascinating but because I keep finding new research that blows my mind.

It's what I love about science in general, really.  This won't be any shock to regular readers of Skeptophilia -- I'm always seeming to bump into just-published papers on crazy cool topics, especially having to do with astronomy, biology, physics, geology, and paleontology, and then telling you about them here.  As I've said before, delve into science if you want to guarantee you'll never be bored again.

Today's topic came to me via a paper in Physical Review Letters by Barbara Šoda and Achim Kempf (of the University of Waterloo), and Vivishek Sudhir (of MIT), and made reference to a phenomenon I'd never heard of before: the Unruh effect.  It was named for Canadian physicist William Unruh, who did some of the earliest theoretical work on it, but major contributions were made by Stephen Fulling of the United States and Paul Davies of England.  And it all has to do with what an observer would see if (s)he was accelerating rapidly through empty space.  (Although in a moment we'll have to redefine what we mean by "empty," because a vacuum isn't actually empty at all.)

We're all familiar with the science fiction movie image of what it looks like to jump to superluminal speeds.  Every time the commander of a spaceship shouts "jump to warp!" or "engage hyperdrive!", they're treated to a view like this:

[Image is in the Public Domain courtesy of NASA]

There's no way to tell if this is what such a space traveler going faster than light would actually see, because (1) no one has ever actually experienced it, and (2) it's almost certainly impossible anyway (Cf. the Special Theory of Relativity and my summary of all the papers written on the topic as "Yay!  Einstein wins again!")  But even if actual warp drive and faster-than-light velocities aren't possible, what would it look like if you gazed out of the front window of a spaceship that was accelerating rapidly toward the speed of light?

The idea of stars turning into blurred streaks as we whiz past, as engaging as it is, doesn't seem to capture what we'd actually see in such a situation.  

The Unruh effect is what we'd observe.  This is a quantum effect caused by accelerating in a vacuum, which would cause an apparent increase in temperature ahead of us -- it would appear to have a thermal glow.  The reason is that seemingly empty space isn't empty in the conventional sense.  It is filled with quantum fields -- which exist everywhere in the universe -- and the word "empty" here means that those fields are in the ground state, the lowest possible energy configuration space can have.

To a stationary observer, it would indeed appear empty.  But to our space traveler, the rapid acceleration would cause an apparent increase in temperature ahead of the spacecraft.  A stationary observer would consider the empty space ahead as being in the ground state; an accelerating space traveler would measure it to be in a mixed state, in thermodynamic equilibrium with a non-zero ambient temperature.

The vacuum of space would seem to glow.  That's the Unruh effect.

Just like our discussion on Monday of simultaneity, asking "so what temperature is it really?" is a meaningless question.  The measured temperature -- like just about anything else you could measure -- depends on your frame of reference.  The only thing that every observer, in every reference frame (accelerating or not), measures as precisely the same is the speed of light.  (In fact, it's the constancy of the speed of light in every frame of reference that springboarded our understanding of the relativistic nature of the universe, and directly gave rise to all of the other bizarre effects in the model.)

Nobody has actually observed the Unruh effect; the temperature increase is small, and the acceleration required is huge.  Even if you could achieve those accelerations, you'd have to eliminate all the other possible sources of a perceived increase in temperature, which are numerous.

Well -- no one has observed it yet.  Šoda, Kempf, and Sudhir believe they have found a way to isolate the system so that the only possible source of temperature rise is due to the detector's acceleration.  "To see this effect in a short amount of time, you'd have to have some incredible acceleration," Sudhir said, in an interview with Science Daily.  "If you instead had some reasonable acceleration, you'd have to wait a ginormous amount of time -- longer than the age of the universe -- to see a measurable effect...  We believe we have found a way to shave that time down to a few hours.  Now at least we know there is a chance in our lifetimes where we might actually see this effect.  It's a hard experiment, and there's no guarantee that we'd be able to do it, but this idea is our nearest hope."

So with luck, this team might have found a way to observe something that no one has ever seen before -- what it would be like to look through the front window of a rapidly-accelerating spaceship.  It may not be as dramatic as the stars-turned-into-streaks effect known and loved by fans of Star Trek and Star Wars, but it's still amazingly cool that we have a chance to see, for real, what they'd see.

Engage hyperdrive!

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The stubbornly persistent illusion

I was driving through Ithaca, New York a while back, and came to a stoplight, and the car in front of me had a bumper sticker that said, "Time is that without which everything would happen at once."

I laughed, but I kept thinking about it, because in one sentence it highlights one of the most persistent mysteries of physics: why we perceive a flow of time.  The problem is, just about all of the laws of physics, from quantum mechanics to the General Theory of Relativity, are time-reversible; they work equally well in forward as in reverse.  Put another way, most physical processes look the same both ways.  If I were to show you a short video clip of two billiard balls colliding on a pool table, then the same clip backwards, it would be hard to tell which was which.  The Laws of Conservation of Momentum and Conservation of Energy that describe the results of the collision work in either direction.

There are exceptions, though.  The Second Law of Thermodynamics is the most commonly-cited one: closed systems always increase in entropy.  It's why when I put sugar in my coffee in the morning and stir it, the sugar spreads through the whole cup.  If I were to give it one more stir and all the sugar molecules were to come back together as crystals and settle out on the bottom, I'd be mighty surprised.  I might even wonder if someone had spiked the sugar bowl with something other than sugar.

In fact, that's why I had to specify a "short clip" in the billiard ball example.  There is a time-irreversible aspect of such classical physics; as the balls roll across the table, they lose momentum, because a little of the kinetic energy of their motion leaks away as thermal energy due to friction with the surface.  When they collide, a little more is lost because of the sound of the balls striking each other, the (slight) physical deformation they undergo, and so on.  So if you had a sensitive enough camera, or a long enough clip, you could tell which was the forward and which the reverse clip, because the sum of the kinetic energies of the balls in the forward clip would be (slightly) greater before the collision than after it.

But I am hard-pressed to see why that creates a sense of the flow of time.  It can't be solely from our awareness of a movement toward disorder.  When there's an energy input, you can generate a decrease in entropy; it's what happens when a single-celled zygote develops into a complex embryo, for example.  There's nothing in the Second Law that prevents increasing complexity in an open system.  But we don't see those situations as somehow running in reverse; entropy increase by itself doesn't generate anything more than expected set of behaviors of certain systems.  How that could affect how time is perceived by our brains is beyond me.

The problem of time's arrow is one of long standing.  Einstein himself recognized the seeming paradox; he wrote, "The distinction between past, present, and future is only a stubbornly persistent illusion."  "Persistent" is an apt word; more than sixty years after the great man's death, there was an entire conference on the nature of time, which resolved very little but giving dozens of physicists the chance to defend their own views, and in the end convinced no one.

It was, you might say, a waste of time.  Whatever that means.

One of the most bizarre ideas about the nature of time is the one that comes out of the Special Theory of Relativity, and was the reason Einstein made the comment he did: the block universe.  I first ran into the block universe model not from Einstein but from physicist Brian Greene's phenomenal four-part documentary The Fabric of the Cosmos, and it goes something like this.  (I will append my usual caveat that despite my bachelor's degree in physics, I really am a layperson, and if any physicists read this and pick up any mistakes, I would very much appreciate it if they'd let me know so I can correct them.)

One of the most mind-bending things about the Special Theory is that it does away with simultaneity being a fixed, absolute, universal phenomenon.  If we observe two events happening at exactly the same time, our automatic assumption is that anyone else, anywhere in the universe, would also observe them as simultaneous.  Why would we not?  But the Special Theory shows conclusively that your perception of the order of events is dependent upon your frame of reference.  If two individuals are in different reference frames (i.e. moving at different velocities), and one sees the two events as simultaneous, the other will see them as sequential.  (The effect is tiny unless the difference in velocities is very large; that's why we don't experience this under ordinary circumstances.)

This means that past, present, and future depend on what frame of reference you're in.  Something that is in the future for me might be in the past for you.  This can be conceptualized by looking at space-time as being shaped like a loaf of bread; the long axis is time, the other two represent space.  (We've lost a dimension, but the analogy still works.)  The angle you are allowed to slice into the loaf is determined by your velocity; if you and two friends are moving at different velocities, your slice and theirs are cut at different angles.  Here's a picture of what happens -- to make it even more visualizable, all three spatial dimensions are reduced to one (the x axis) and the slice of time perceived moves along the other (the y axis).  A, B, and C are three events, and the question is -- what order do they occur in?

[Image licensed under the Creative Commons User:Acdx, Relativity of Simultaneity Animation, CC BY-SA 4.0]

As you can see, it depends.  If you are taking your own velocity as zero, all three seem to be simultaneous.  But change the velocity -- the velocities are shown at the bottom of the graph -- and the situation changes.  To an observer moving at a speed of thirty percent of the speed of light relative to you, the order is C -> B -> A.  At a speed of fifty percent of the speed of light in the other direction, the order is A -> B -> C.

So the tempting question -- who is right? what order did the events really occur in? -- is meaningless.

Probably unnecessarily, I'll add that this isn't just wild speculation.  The Special Theory of Relativity has been tested hundreds, probably thousands, of times, and has passed every test to a precision of as many decimal places as you want to calculate.  (A friend of mine says that the papers written about these continuing experiments should contain only one sentence: "Yay!  Einstein wins again!")  Not only has this been confirmed in the lab, the predictions of the Special Theory have a critical real-world application -- without the equations that lead directly to the block universe and the relativity of simultaneity, our GPS systems wouldn't work.  If you want accurate GPS, you have to accept that the universe has some seriously weird features.

So the fact that we remember the past and don't remember the future is still unexplained.  From the standpoint of physics, it seems like past, present, and future are all already there, fixed, trapped in the block like flies in amber.  Our sense of time flowing, however familiar, is the real mystery.

But I'd better wrap this up, because I'm running out of time.

Whatever that means.

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Tiny timepieces

One of the most mind-blowing revelations from science in the past two hundred years came out of a concept so simple that a sixth-grader could understand it.

You've all observed that the motion of objects is relative.  Picture a train with glass sides (only so you can see into it from outside).  The train is moving forward at 5 kilometers per hour, with an observer standing next to it watching it roll past.  At the same time, a guy is walking toward the back of the train, also at 5 kilometers per hour.

From the point-of-view of anyone on the train, the walking man is moving at 5 kilometers per hour.  But from the point-of-view of the stationary observer outside the train, it appears like the man on the train isn't moving -- he's just walking in place while the train slides out from under him.  This is what is meant by relative motion; the motion of an object is relative to the frame of reference you're in.  We don't observe the motion of the Earth because we're moving with it.  It, and us, appear to be motionless.  In the frame of reference of an astronaut poised above the plane of the Solar System, though, it would seem as if the Earth was a spinning ball soaring in an elliptical path around the Sun, carrying us along with it at breakneck speed.

With me so far?  Because here's the simple-to-state, crazy-hard-to-understand part:

Light doesn't do that.

No matter what reference frame you're in -- whether you're moving in the same direction as a beam of light, in the opposite direction, at whatever rate of speed you choose -- light always travels at the same speed, just shy of 300,000,000 meters per second.  (Nota bene: I'm referring to the speed of light in a vacuum.  Light does slow down when it passes through a transparent substance, and this has its own interesting consequences, but doesn't enter into our discussion here.)

It took the genius of Albert Einstein to figure out what this implied.  His conclusion was that if the speed of light isn't relative to your reference frame, something else must be.  And after cranking through some seriously challenging mathematics, he figured out that it wasn't one "something else," it was three: time, mass, and length.  If you travel near the speed of light, in the frame of reference of a motionless observer your clock would appear to run more slowly, your mass would appear greater, and your length appear shorter.  (Where it starts getting even more bizarre is that if you, the one moving near light speed, were to look at the observer, you'd think it was him whose watch was running slow, who had a greater mass, and who was flattened.  Each of you would observe what seem to be opposite, contradictory measurements... and you'd both be right.)

All of this stuff I've been described is called the Special Theory of Relativity.  But Einstein evidently decided, "Okay, that is just not weird enough," because he did another little thought experiment -- this one having to do with gravity.  Picture two people, both in sealed metal boxes.  One of them is sitting on the surface of the Earth (he, of course, doesn't know that).  The other is out in interstellar space, but is being towed along by a spacecraft at an acceleration of 9.8 meters per second (the acceleration due to gravity we experience here on the Earth's surface).  The two trapped people have a communication device allowing them to talk to each other.  They know that one is sitting on a planet's surface and the other is being pulled along by a spaceship, but neither knows which is which.  Is there anything they could do, any experiment they could perform, anything that would allow them to figure out who was on a planet and who was being accelerated mechanically?

Einstein concluded that the answer was no.  Being in a gravitational field is, for all intents and purposes, exactly the same as experiencing accelerated motion.  So his conclusion was that the relativistic effects I mentioned above -- time dilation, mass increase, and shortening of an object's length -- not only happen when you move fast, but when you're in a strong gravitational field.  If you've seen the movie Interstellar, you know all about this; the characters stuck on the planet near the powerful gravitational field of a black hole were slowed down from the standpoint of the rest of us.  They were there only a year by their own clocks, but to everyone back home on Earth, decades had passed.

Maybe you're thinking, "But isn't the Earth's gravitational field pretty strong?  Shouldn't we be experiencing this?"  The answer is that we do, but the Earth's gravity simply isn't strong enough that we notice.  If you travel fast -- say on a supersonic airline -- your clock does run slow as compared to the ones down here on Earth.  It's just that the difference is so minuscule that most clocks can't measure the difference.  Even if supersonic seems fast to us, it's nearly standing still compared to light; if you're traveling at Mach 1, the speed of sound, you're still moving at only at about one ten-thousandth of a percent of the speed of light.  The same is true for the gravitational effects; time passes more slowly for someone at the bottom of a mountain than it does for someone on top.  So on any ordinary scale, there are relativistic effects, they're just tiny.

[Image licensed under the Creative Commons Mysid, Spacetime lattice analogy, CC BY-SA 3.0]

But that's what brings the whole bizarre topic up today -- because our ability to measure those tiny, but very real, effects just took a quantum leap (*rimshot*) with the development of a technique for measuring the "clocks" experienced by a cluster of atoms only a millimeter long.  A stack of about 100,000 strontium atoms that had been cooled down to near absolute zero were tested to see what frequency of light would make their electrons jump to the next energy level -- something that has been measured to a ridiculous level of accuracy -- and it was found that the ones at the bottom of the stack (i.e. nearer to the Earth's surface) required a different frequency of light to jump than the ones at the top.  The difference was incredibly small -- about a hundredth of a quadrillionth of a percent -- but the kicker is that the discrepancy is exactly what Einstein's General Theory of Relativity predicts.

So Einstein wins again.  As always.  And if you're wondering, it means your feet are aging slightly more slowly than your head, assuming you spend as much time right-side-up as you do upside-down.  Oh, and your feet are heavier and flatter than your head is, but not enough to worry about.

All of this because of pondering whether light behaved like someone walking on a train, and if someone being towed by an accelerating spaceship could tell he wasn't just in an ordinary gravitational field.  It brings home the wonderful quote by physicist Albert Szent-Györgyi (himself a Nobel Prize winner) -- "Discovery consists of seeing what everyone has seen, and thinking what no one has thought."

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My dad once quipped about me that my two favorite kinds of food were "plenty" and "often."  He wasn't far wrong.  I not only have eclectic tastes, I love trying new things -- and surprising, considering my penchant for culinary adventure, have only rarely run across anything I truly did not like.

So the new book Gastro Obscura: A Food Adventurer's Guide by Cecily Wong and Dylan Thuras is right down my alley.  Wong and Thuras traveled to all seven continents to find the most interesting and unique foods each had to offer -- their discoveries included a Chilean beer that includes fog as an ingredient, a fish paste from Italy that is still being made the same way it was by the Romans two millennia ago, a Sardinian pasta so loved by the locals it's called "the threads of God," and a tea that is so rare it is only served in one tea house on the slopes of Mount Hua in China.

If you're a foodie -- or if, like me, you're not sophisticated enough for that appellation but just like to eat -- you should check out Gastro Obscura.  You'll gain a new appreciation for the diversity of cuisines the world has to offer, and might end up thinking differently about what you serve on your own table.

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

Tweets from time travelers

So, you know how I said yesterday that science has an advantage over woo-woo beliefs, because the woo-woos never seem to see when an idea is so phenomenally silly that it deserves to be rejected out of hand?  And that therefore, we should be listening to the scientists, not the woo-woos?

I take it back.

This near-instantaneous retraction has come about because of a paper published by Michigan Technological University astrophysicists Robert Nemiroff and Teresa Wilson entitled "Searching the Internet for Evidence of Time Travelers."  Nemiroff and Wilson note that time travel into the future is possible (in fact, that's kind of what we're doing right now); they also make the less obvious point that the rate at which you travel into the future can differ from another person's, because of the Special Theory of Relativity.  Time travel into the past is, they say, "more controversial," although there are some features of the General Theory of Relativity that may allow it.

[Image from Dr. Who courtesy of the Wikimedia Commons]

It is, of course, the latter possibility that is of the most interest.  It's been riffed on in countless novels, short stories, and movies -- I even played around with the notion myself, in my novel Lock & Key.  Rips in the space-time continuum account for at least a hundred plots on Star Trek alone.

But as a reality?  I'm kind of doubtful.  And so far, I've got nothing against what Nemiroff and Wilson have written.  But wait till you hear how they tried to detect time travelers:

Time travel has captured the public imagination for much of the past century, but little has been done to actually search for time travelers. Here, three implementations of Internet searches for time travelers are described, all seeking a prescient mention of information not previously available. The first search covered prescient content placed on the Internet, highlighted by a comprehensive search for specific terms in tweets on Twitter. The second search examined prescient inquiries submitted to a search engine, highlighted by a comprehensive search for specific search terms submitted to a popular astronomy web site. The third search involved a request for a direct Internet communication, either by email or tweet, pre-dating to the time of the inquiry.

Yup.  They were trying to find some place that a time traveler slipped up, and tweeted something last August like "On January 7, 2014, people in the northern part of the USA should plan on dressing warmly.  #fuckingcold"

Specifically, they looked for mentions of Pope Francis prior to his election, and Comet ISON prior to its discovery.  Not surprisingly, Nemiroff and Wilson stated in the conclusion of their paper, "No time travelers were discovered."

My question is how, if these people from the future are smart enough to come back here, they would also simultaneously be dumb enough to get onto Twitter and post something that gave away the game.  I'd think they'd be pretty careful about that, wouldn't  you?  Not only would it reveal their identities as time travelers, it could also potentially change what for them is the past, and you know that would create some sort of temporal paradox that would monumentally screw up everything, and we don't even have Geordi LaForge around to fix things.

Nemiroff was interviewed by Raw Story about his research, and the interviewer actually asked him why he thought that a time traveler would use Twitter at all.  "Twitter is an echo of what’s going on in society," he replied, "so I’d ask you, 'Why do you think a traveler wouldn’t use Twitter?'  Besides, it wouldn’t have to be the traveler himself who used Twitter.  Someone could have overheard him say something prescient, and put that on Twitter in a way that would be magnified through conversation."

He then went on to relate the old joke about the guy who was searching for his lost car keys under a streetlight, and a cop comes along to help him.  After a fruitless search, the cop asks, "Are you sure you lost your car keys here?"  And the guy says, "No, I lost them over there."  The cop says, in some annoyance, "Then why are you looking for them here?"  And the guy says, "Because there's better light over here."

Nemiroff says that his search on Twitter is like the guy searching under the streetlight; "You have to go where the information is."  To which I respond: I don't think you understood the joke.  The whole reason that it's funny is because the keys weren't there.  Also, very possibly, because the guy looking for the car keys was a wingnut.  This is definitely not the kind of joke that you would use in support of what you're doing.

Nemiroff, though, isn't discouraged.  "We didn’t prove that time travelers aren’t here," he said, "only that we couldn’t find them."

Now, don't get me wrong, I have nothing with a couple of scientists having a little lighthearted fun, once in a while.  But Nemiroff and Wilson might want to prepare themselves for a nomination for the 2014 IgNobel Prizes, awarded to the strangest, silliest research published each year.

So despite Nemiroff's and Wilson's best efforts, they ended up like Monty Python's "Camel Spotters;" they spotted nearly one time traveler.  Just about what I'd expect, given their experimental protocol.  So I should wrap up this post and go and get another cup of coffee, especially considering that because of the Great February 2014 Coffee Bean Shortage, I'll soon be...

Oops.