One proposed model for dark energy known as the chameleon field has been put to the test, and failed.
It’s What’s For Dinner
A new paper in Physical Review Letters has led to popular science headlines wondering “Is dark energy eating dark matter?” but that’s not what the paper claims at all.
The Phantom Menace
We know the universe is expanding, and we know it is doing so at an ever increasing rate. This cosmic acceleration is part of the evidence for dark energy, which current observations put at about 68% of the observable universe. But beyond its existence as some kind of energy, we’re still trying to determine just what dark energy is.
Sound It Out
Imagine a stadium filled with people. With everyone is in their seats, waiting for the game to begin, there is an undercurrent of noise. A few words between friends, the scuffle of shoes, the creak of a chair. All of these little sounds fill the stadium with a background of white noise. A similar “white noise” occurs with galaxies in our universe, and it helps us understand dark energy.
Like a BOSS
Dark energy is perhaps the least understood aspect of modern cosmology. We first obtained evidence of its existence via the 1998 discovery that the universe is not only expanding (which we’ve long known), but that the rate of expansion is accelerating. This was done by observing the redshifts of distant supernovae, and won the discovers a Nobel prize. Since then observations of the cosmic microwave background have found that dark energy makes up about 70% of the matter-energy in the universe. This is consistent with observations of acceleration.
What a Rube
Recently there was an article by Tim Reyes asking if the standard cosmological model is a Rube Goldberg machine. The idea is that so many ill-fitting ideas have been put together that it seems unreasonably complex. I’ve used a similar criticism against certain models through the phrase “tweak theories are weak theories.” Given the latest implications that the Higgs field may contradict inflation, and the BICEP2 results may not hold up, should we really think of standard cosmology more as a tweak theory than a robust model?
The 5th Dimension
From measurements of distant supernovae, we now know our universe is not only expanding, but that it is expanding at an ever increasing rate. This cosmic acceleration is driven by what we call dark energy. While we can see the effects of dark energy, and we know it makes up about 68% of our universe, we don’t really know what dark energy actually is. That means while the experimentalists scurry to get more data, the theorists work frantically to explain what’s going on.
Gravity Check
Newton’s law of gravity states that between any two masses there is a gravitational force. The strength of that force depends not only on the masses, but on the distance between those masses, following what is known as an inverse square relation. Newton felt that this inverse square relation was exact, but is it?
Energy Matters
How do we know that dark energy isn’t due to some kind of repulsive matter? If we speculate on the effects of repulsive matter, we find that what we predict isn’t what we see. Whatever dark energy is, observational evidence shows it isn’t matter.