Posted by
Rob on Monday, September 29, 2008 10:18:28 PM
On one of my newsfeeds this Science Daily article was posted:
Dark Energy: Is It Merely an Illusion?
ScienceDaily (Sep. 29, 2008) —
Dark energy is at the heart of one of the greatest mysteries of modern
physics, but it may be nothing more than an illusion, according
physicists at Oxford University.
The problem facing
astrophysicists is that they have to explain why the universe appears
to be expanding at an ever increasing rate. The most popular
explanation is that some sort of force is pushing the accelerating the
universe's expansion. That force is generally attributed to a
mysterious dark energy.
Although dark energy may seem a bit
contrived to some, the Oxford theorists are proposing an even more
outrageous alternative. They point out that it's possible that we
simply live in a very special place in the universe - specifically,
we're in a huge void where the density of matter is particularly low.
The suggestion flies in the face of the Copernican Principle, which is
one of the most useful and widely held tenants in physics...
(Actually, it's not. Even if he did mean "tenets". I would be surprised if 5% of physicists knew what it was.)
The concept of "dark energy" is really "anti-gravity". That is, Einstein wanted his universe to be eternal and static, but gravity was always pulling everything into a black hole. Newton had suggested that a uniform distribution of matter extending to infinity would not collapse. But an ant's sneeze, over an eternity of time, would have caused the collapse of Newton's universe. And Einstein's universe was even more unstable than Newton's, since spacetime was itself curved by gravity even if it were homogeneous. In perplexity, Einstein included anti-gravity, made it proportional to volume (sort of like the gas pressure in a closed container), and achieved his static eternity. You will note how little empirical evidence played a part or even why antigravity had to be made proportional to volume in this metaphysical theory. Then Hubble observed galactic expansion, Einstein realized the Universe didn't have to be static, and called his dark-energy term "his biggest mistake".
The evidence for dark energy is slim to none. It mostly satisfies the question "Why is our Universe look flat today?" Because Einstein's universe even with a Big Bang, would take 1:10^60 accuracy (about 1 grain of salt precision in the mass of the known universe) for the Big Bang to avoid too fast or too slow expansion. In other words, it looks designed. So dialing in anti-gravity, and letting it vary with time makes the problem go away. (So would invoking angels, boojums or God, which have the added benefit of being more understandable than "dark energy".) [There is the observation of supernova 1A's in distant galaxies being dimmer than expected, which is attributed to cosmic acceleration rather than, say, dust. I'd put my bets on dust.]
This paper argues that we can solve the problem by making the Universe bigger than we can see, and hence more dense outside our little bubble, which then appears to us to have a deficit of matter to explain its flatness. So we sacrifice homogeneity for boojums. Though no one has done the calculation on just how precise that inhomogeneity has to be...