Sep 01 2009
When all the stars go away
By Ian Woolf
At the Powerhouse Museum’s ‘Einstein Lecture’, U.S Theoretical Physicist Lawrence Krauss spoke about the invisible dark energy required by the most popular theory of cosmology. He wrapped up by explaining the dark future for the Universe when all the stars go away.
Hey, isn't that philosophy?
That’s the short story. Now here it is in a slightly longer version…
According to Professor Joss Bland-Hawthorn, the predictions of Big Bang theory models don’t match the observations. Dark matter is required to explain how stars can move in galaxies that appear to lack enough matter to provide enough gravity to pull them around.
Lawrence Krauss - an excellent presenter
Krauss started by telling us that Edwin Hubble observed that the Universe appears to be rushing away from us in all directions. How can this be? The best guess seems to be that empty space itself is expanding, including the space inside atoms and sub-atomic particles.
Slipping away from us, faster than the speed of light
If you match the predictions against the observations of exploding stars – supernovas – you can make an educated guess as to whether the expansion will continue, stop or reverse. The evidence of observations of distant exploding stars seems to indicate the expansion of space will continue and that it’s also accelerating.
All the stars and galaxies will eventually move away from us, faster than light.
The sky will be black, and there will be no more astronomy.
General relativity allows space to expand faster than light, even though special relativity famously forbids anything traveling through space faster than light. Cosmologists say this with a straight face.
Where is the energy to expand space coming from? We can’t observe any source of energy that would expand space this way, so because we can’t see it, cosmologists call the energy powering the expansion ‘dark energy’.
Cosmologists guess that Albert Einstein’s old discarded idea of a “cosmological constant” may be the source of energy we can’t see. The cosmological constant is a force that acts to move masses apart: the opposite of gravity.
The best guess for how this cosmological constant acts in the world seems to be that the energy of quantum fluctuations of the vacuum are the source of dark energy.
The energy of the vacuum is powered by the appearance and disappearance of quantum particles in a very very tiny amount of time: Planck time, 10 to the -40 seconds. In this time, photons of light appear, then disappear, as if the Universe borrows the energy on credit, and then pays it back as fast as possible. These “virtual photons” of light exist just long enough to be detected and measured.
They’re real, even though they slightly break the laws of thermodynamics.
What looks like empty space is actually fizzing with energy as these virtual photons appear and disappear.
In the Casimir effect, these virtual photons can push two plates together if they are already very close. If the plates are close enough together that the distance between them is less than the wavelengths of some colours of light, then photons with those wavelengths can’t appear between the plates, only outside the plates. This means that there are more of these virtual photons appearing and disappearing on the outside of the plates than between them. This difference causes a pressure that pushes the plates together. The pressure comes from there being “thinner nothing” between the plates and “thicker nothing” outside them! Or more colours outside the plates and less colours between them. The point is that when you set the plates up, they really do get pushed together by the extra photons outside the plates. You just got a very tiny amount of something for nothing.
Krauss showed us an animation of how the vacuum energy fluctuated inside the protons that sit inside the nucleus at the heart of every atom of matter.
Particle physicists have estimated how much vacuum energy there is in the Universe. The problem is that it’s too small by over a hundred orders of magnitude to be the source of invisible energy that expands space to explain the stars moving away from us. Either dark energy cosmology is wrong, or particle physics is wrong, or Einstein’s theory of gravity is wrong. The observations made at the Large Hadron Collider will help us find out which is the case.
So Big Bang cosmology requires dark energy, dark matter and, more recently, “dark carbon” because the model predicts more carbon than we observe in the Universe. I figure if your model keeps making predictions of things that we just can’t see, maybe you should stop assuming these things are just invisible or “dark”? Maybe the model is just wrong?
As I left the Lawrence Krauss talk, something was niggling at me, but I couldn’t form it into a question until three days later. So, here it is:
If space everywhere is expanding at an accelerated rate as shown by the supernova evidence, and this includes the space inside atoms and sub-atomic particles like protons, then isn’t all of matter expanding and growing too? And when the subatomic particles get too big from the accelerating expansion, won’t they all pop and stop being matter? Is there a different kind of Big Bang in our future when all matter explodes as the space inside it expands faster than the speed of light?
(We’re going to try to get hold of Lawrence Krauss to address this question – but if you have any thoughts on the answer – please let us know! Ian’s sleep at night depends on it! – ed)
More Lawrence Krauss here …
“Things are going to get unimaginably worse and they’re never going to get better again…”
“Supernova … are great standard candles … it’s fortunate for us that they explode because every atom in your body came from one that exploded.”
Hear why Lawrence Krauss wants to assign “a graduate student to each galaxy”.
Lawrence Krauss replied … here’s what he has to say. I hope this comforts you Ian!
“space is not expanding everywhere.. systems which are gravitationally bound, like our galaxy, and the earth, are not expanding, and neither is the space inside atoms.. so you are safe.”