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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Into the expanse

Last week, I did a post about dark matter and dark energy -- and how those could potentially drive a reworking of what we know about physics.  Today, there's another finding that is causing some serious head-scratching amongst the physicists:

The universe may be expanding faster than we thought.  Not by a small amount, either.  The difference amounts to about 9%.  Further, this means that the universe might also be younger than we'd thought -- by almost a billion years.

This rather puzzling conclusion is the result of work by a team led by Adam Riess, of Johns Hopkins University.  At issue here is the Hubble constant, the rate of outward expansion of spacetime.  It's not an easy thing to measure.  The usual method has been to use what are called standard candles, which need a bit of explanation.

The difficulty with accurately measuring the distance to the nearest stars is a problem that's been apparent for several centuries.  If two stars are equally bright as seen from Earth, it may be that they're shining at the same luminosity and are the same distance.  It's more likely, however, that they're actually at different distances, but the brighter one is farther away.  But how could you tell?

For the nearest stars, we can use parallax -- the apparent movement of the star as the Earth revolves around the Sun.  Refinements in this technique have resulted in our ability to measure a parallax shift of 10 microarcseconds -- one ten-millionth of 1/3600th of the apparent circumference of the sky.  This translates to being able to measure distances of up to 10,000 light years this way.

But for astronomical objects that are farther away, parallax doesn't work, so you have to rely on something that tells you the star's intrinsic brightness; then you can use that information to figure out how far away it is.  There are two very common ones used:

1. Cepheid variables.  Cepheids are a class of variable stars -- ones that oscillate in luminosity -- that have an interesting property.  The rate at which their brightness oscillates is directly proportional to its actual luminosity.  So once you know how fast it's oscillating, you can calculate how bright it actually is, and from that determine how far away it is.
2. Type 1a supernovae.  These colossal stellar explosions always result in the same peak luminosity.  So when one occurs in a distant galaxy, astronomers can chart its apparent brightness peak -- and from that, determine how far away the entire galaxy is.

A Cepheid variable [Image is in the Public Domain, courtesy of the Hubble Space Telescope]

So the standard candle method has allowed us to estimate the distances to other galaxies, you can combine that information with its degree of red shift (a measure of how fast it's moving away from us) to estimate the rate of expansion of space.

And here's where the trouble lies.  Previous measurements of the rate of expansion of space, made using information such as the three-degree microwave background radiation, have consistently given the same value for the Hubble constant and the same age of the universe -- 13.7 billion years.  Riess's measurement of standard candles in distant galaxies is also giving a consistent answer... but a different one, on the order of 12.8 billion years.

"It’s looking more and more like we’re going to need something new to explain this," Riess said.

John Cromwell Mather, winner of the 2006 Nobel Prize in Physics, was even more blunt.  "There are only two options," Mather said.  "1. We’re making mistakes we can’t find yet. 2. Nature has something we can’t find yet."

"You need to add something into the universe that we don’t know about,” said Chris Burns, an astrophysicist at the Carnegie Institution for Science.  "That always makes you kind of uneasy."

To say the least.  Throw this in with dark matter and dark energy, and you've got a significant piece of the universe that physicists have not yet explained.  It's understandable that it makes them uneasy, since finding the explanation might well mean that a sizable chunk of our previous understanding was misleading, incomplete, or simply wrong.

But it's exciting.  Gaining insight into previously unexplained phenomena is what science does.  My guess is we're awaiting some astrophysicist having a flash of insight and crafting an answer that will blow us all away, much the way that Einstein's insight -- which we now call the Special Theory of Relativity -- blew us away by reframing the "problem of the constancy of the speed of light."  Who this century's Einstein will be, I have no idea.

But it's certain that whoever it is will overturn our understanding of the universe in some very fundamental ways.

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I grew up going once a summer with my dad to southern New Mexico and southern Arizona, with the goal of... finding rocks.  It's an odd hobby for a kid to have, but I'd been fascinated by rocks and minerals since I was very young, and it was helped along by the fact that my dad did beautiful lapidary work.  So while he was poking around looking for turquoise and agates and gem-quality jade, I was using my little rock hammer to hack out chunks of sandstone and feldspar and quartzite and wondering how, why, and when they'd gotten there.

Turns out that part of the country has some seriously complicated geology, and I didn't really appreciate just how complicated until I read John McPhee's four-part series called Annals of the Former World.  Composed of Basin and Range, In Suspect Terrain, Rising from the Plains, and Assembling California, it describes a cross-country trip McPhee took on Interstate 80, accompanied along the way with various geologists, with whom he stops at every roadcut and outcrop along the way.  As usual with McPhee's books they concentrate on the personalities of the people he's with as much as the science.  But you'll come away with a good appreciation for Deep Time -- and how drastically our continent has changed during the past billion years.

[Note:  If you order this book using the image/link below, part of the proceeds will go to support Skeptophilia!]