A Hundred Years Ago, the Universe Was Not Expanding

Just over a hundred years ago, in 1915, Einstein introduced general relativity to the world.  It was so complex that it was said that only three people in the world understood it.  That is not actually true; quite a few people had a pretty good idea of what Einstein was proposing.  What is true is that, a hundred years later, our computers are not up to the task of calculating solutions to his equations, as David Wilshire said in 2008:

“But Einstein’s equations (1915) are in general so complex that we cannot solve them for the distribution of matter we actually see, even on a computer.”

Many things have happened in the last hundred years.  When I was a child, the concept of what I am doing right now was a distant dream: using a computer as a typewriter as well as a telegraph machine– with color illustrations.  Computers brew coffee, drive cars, and help us observe galaxies 10 billion light-years away.   We have decided that the Universe is 13.8 billion years old, is expanding and is flat, but with no edges and no corners.

One of the things that has happened relatively (!) recently is that a mysterious quantity, dark energy, has been proposed as an explanation for a puzzling observation: the rate of expansion of the Universe actually appears to be speeding up.  This really doesn’t make sense, particularly because if it were true, eventually the entire Universe would be ripped apart– possibly soon, as one recent science-fiction short story has made painfully real for us.

As David Wiltshire explained in 2008 in a simple overview and in this highly technical paper describes, this is only an apparent problem due to the inhomogeneity of matter distribution that was created when the Universe first appeared.  Matter is inhomogeneously distributed because, due to the uncertainty principle (with which Einstein famously had a lot of trouble), when space and time first appeared, one couldn’t be sure whether there was matter or space in any particular place.

As a result of this inhomogeneity in the beginning, at the present time there are huge voids in the Universe– voids within which there is virtually no matter at all, only space.  We exist within a filament or bubble which contains a significant density of matter; virtually all stars, galaxies, and so forth exist within these locally dense areas.  The Universe as a whole can be thought of as a huge Swiss cheese, a very tenuous one.

Because of this, all stars that are observed to be travelling away from us following the Hubble Constant are apparently also speeding up their withdrawal.  This apparent speeding up is due to our local clock time, which has slowed down in relation to the average clock time in the Universe; the average clock time runs faster because it is measured within those voids.

In other words, the apparent speeding up of cosmic expansion is due not to a mysterious dark energy (which has not yet been found) but to normal Einsteinian mechanics.  Every “standard candle” we observe that is telling us how far away it is and what the Hubble Constant is, is located within a region of space that contains matter and thus has its time slowed down relative to the clocks within the voids.  Of course, those voids don’t contain any clocks because they are empty, but if they did, they would run faster than ours.

Empty space is expanding at a rate that tells us that it is negatively curved, like a saddle; our space, the space that contains matter, is not expanding because its gravity binds it together.  Here is a quote from the abstract of the latest paper:

“Generic averages of Einstein’s equations in inhomogeneous cosmology lead to models with non-rigidly evolving average spatial curvature, and different parametrizations of apparent cosmic acceleration. The timescape cosmology is a viable example of such a model without dark energy. ”

It’s pretty complicated, but eventually the majority of cosmologists will get their heads around it and forget about searching for dark energy.  It has only been ten years or so since Wiltshire pointed out that our clocks are running slower than the Universe’s average clock, and less than a hundred years since Edwin Hubble discovered (in 1922-23) that there was a larger Universe outside the Milky Way– a universe that, he announced in his first published paper in 1929, is expanding.

(Here is David Wiltshire’s latest paper, with Lawrence H Dam and Asta Heinesen.  Here are more references to the absence of dark energy: an article in the International Business Times from 9/14/2017 where the theory is called “timescape cosmology”; and an article from Science April 3, 2017) 

(After that, you’re on your own.  See Wikipedia for more information about Edwin Hubble and cosmology)

(photo courtesy of pixabay.com and geralt)

(Please notify me in the comments about any errors)