Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Thursday, May 9, 2019

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.


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!]

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