Science Seen Time One author Colin Gillespie helps you understand the physics of your world.
Expanding Space, Expanding Minds
Understanding physics can be satisfying. Understanding physics some physicists don’t understand brings super-satisfaction.
Many think they can’t understand physics. Seems to me that often it is physicists they can’t understand. I think anybody who can figure how to travel to another country can, with no more effort, understand a lot of physics. With two provisos: It should be explained in plain language; and it should have an explanation (lots of physics doesn’t).
I’ve mentioned how the 2011 Nobel Prize for physics was awarded for discovering that space has been expanding at an accelerating rate for billions of years. The acceleration gives seeming substance to Dark Energy, yet it is a label with no explanation.
How can space expand? The concept is not easy to understand and is controversial. Many physicists say that it doesn’t. For example, Marcus Chown, a British physicist, science writer and cosmology consultant to New Scientist, once asked:
How is it possible for space, which is utterly empty, to expand? How can nothing expand?
Several physicists replied, assuring him that space is not expanding. They should know better. As far back as 1929 American astronomer Edwin Hubble’s now-famous measurements of galactic velocities confirmed Belgian physicist Georges Lemaître’s prediction: Space is expanding. It was of course understood the universe’s gravity must slow down the expansion; someday it may stop and then contract. This was what many thought; that Nobel Prize was for showing they were wrong.
Back to Chown. His premise―that space is nothing―is the problem. Albert Einstein changed his mind about space several times but in the end he said that it is something. The success of general relativity supports this. Indeed recent measurements show space is 70% of the mass-energy of the whole universe. But what exactly is space? If it is most of everything, then surely what it is is worth some careful thought.
Recently, serious scientists (the likes of Abhay Ashtekar, Richard Feynman, Carlo Rovelli and Lee Smolin) have been saying space is not continuous. Albert Einstein said the same thing in a letter to a friend before he died. Many signs say all these scientists are right: Space is granular. It is made of tiny pieces, pieces as in distinct things of a certain size (called the Planck volume), pieces which cannot be divided, pieces which (at least in principle) are counted and not measured.
So, space is made of many somethings. For convenience, let’s call these somethings flecks. Space expanding is this easy: Over time there are more flecks. For this there’s an easy explanation. Just like rabbits with a good supply of carrots, flecks can breed more flecks.
Coming: Stories physics tells about new space
Marcus Chown (1993), New Scientist, 17 April, p. 32
George Johnson (1999), “How Is the Universe Built? Grain by Grain”, The New York Times, December 7; http://faculty.washington.edu/smcohen/320/GrainySpace.html
“Metric expansion of space”, Wikipedia, accessed 4 May 2014, http://en.wikipedia.org/wiki/Metric_expansion_of_space
Image credit: Educational Observatory Institute, http://edu-observatory.org/olli/VD-C2BB/Week5.html