This is apparently the post I wasn’t supposed to publish. I wrote it yesterday, and had it somehow utterly disappear from my HD after a crash. I then was writing it in wordpress and had Firefox crash on it before the first auto save…
In a really cool press release that I got yesterday but couldn’t share (silly embargoes), it was announced that observations of distant galaxies support the idea that Dark Energy is most likely a real force or field that we don’t yet understand (as opposed to it being a side effect of us not understanding gravity – it looks like we really do understand gravity). (image left of galaxy spectra from VIRMOS)
Now, at first look, this doesn’t sound that specific our exciting. In fact, the vagueness of our understanding of Dark Energy (and Dark Matter, but this isn’t a post about Dark Matter), lead many people to randomly announce (often in email) that they “don’t believe in Dark Energy.” I even had one of my colleagues last week tell me that he doesn’t believe in Dark Energy (or Dark Matter, which I’m still not talking about). If astronomers can’t convince random physicists (who will admit they haven’t read any of the findings in the past couple years) that Dark Energy is real, how can we convince the general population.
Admittedly, dark energy is something that we can’t see, can’t taste, can’t touch, can’t measure directly, and can’t even precisely mathematically describe. This makes it somewhat hard to sell as real (although it doesn’t appear to have been to hard a sell for the boogie monster, tooth fairy, and snow yeti). So, this raises the question, how can we know Dark Energy exists?
Well, just like the invisible men and invisible women of fiction are detectable through their footprints (a push on the ground), are detectable from the lamps and other furniture they throw at more visible heroes and villains (pulls on objects), and are detectable through the punches they throw (a very definite push), dark energy is also detectable through the push it exerts on the universe.
Dark energy was first detected in 1998 by supernovae observing teams who were working to measure how the expansion rate of the universe has changed over the 13.7 billion years the universe has been around. They expected that the gravitational mass of everything in the universe on everything else would cause a breaking of the expansion. What they found instead was that some mysterious force / field / extra term on gravity / etc is pushing the universe apart and accelerating the expansion. Since this weirdness didn’t have a name, and the name dark energy wasn’t already in use, the weirdness was named Dark Energy.
Since that fateful discovery, people have been working to figure out if dark energy has always been around, if its push has always been the same. Using supernovae, astronomers were able to figure out that dark energy has been around at least as far back as they can go with supernovae. What they haven’t been able to figure out is if it was something related to us not understanding gravity (a constant, back of the mind concern), or if it real is some sort of field effect that just sort of permeates all of space.
And not knowing makes good astronomers apply for telescope time so these questions can be answered.
In a paper published in Nature today, 51 astronomers led by Luigi Guzzo announced that studies looking at a large selection of galaxies in clusters at high and low redshifts (from the VIMOS VLT Deep Survey and the archived 2dF Galaxy Redshift Survey) have found that the motions of galaxies in clusters at high redshifts indicate that 1) we understand gravity, and 2) dark energy has nothing to do with gravity.
Unfortunately, the press release was a little vague, and perhaps even a little contradictory, and I don’t have a subscription to Nature. Here is what it says:
Within current uncertainties, the measurement of this effect provides an independent indication of the need for an unknown extra energy ingredient in the â€šÃ„Ã²cosmic soupâ€šÃ„Ã´, supporting the simplest form of dark energy, the so-called cosmological constant, introduced originally by Albert Einstein. The large uncertainties do not yet exclude the other scenarios, though.
â€šÃ„ÃºWe have also shown that by extending our measurements over volumes about ten times larger than the VVDS, this technique should be able to tell us whether cosmic acceleration originates from a dark energy component of exotic origin or requires a modification of the laws of gravity,â€šÃ„Ã¹ said Guzzo.
I read this to say, they see evidence of dark energy at high redshifts, it isn’t possible to discard dark energy as not existing, it looks like dark energy isn’t a problem with gravity, but there are error bars, and Guzzo thinks continued analysis will make the error bars tiny enough to end this debate.
It’s a start. And it means dark energy is real.
So stop sending me email 😀