The Black Hole Universe
Is our universe housed in a black hole? Or did it exist before the Big Bang? If so, we could solve the mystery of dark energy—surprisingly, itís all down to the humble neutrino.
May 28, 2010
Your mission, should you choose to accept it, is to go undercover as a neutrino and investigate whether these elusive particles are driving dark energy and if they put the big
in the Big Bang. The operation could take you to a universe inside a black hole, and lead you to investigate whether time stretched before the big bang.
Letís start with a little bit more about your assumed identity as a neutrino. Your mother was a proton who met up with three other protons deep inside a star. There was some nuclear fusion, she transformed herself into a neutron, and you popped out. You didnít stick around very long, though. You have no charge and almost no mass, so you barely interact with the other particles, zipping through space, stars, and planets almost as if they arenít even there.
So far, thatís the standard life story of a neutrino. But Stephon Alexander
, a physicist at Haverford College, Pennsylvania, is shaking up that formulaic plot. What if, he ponders, time and our universe existed before the Big Bang? What if this prior version of the cosmos contracted down to a finite size, bounced, and started to expand outwards again? In that case, neutrinos, usually dismissed as being a ghostly particles with little tangible influence, could have had an extremely profound effect on the cosmos.
Picture yourself as a neutrino in such a contracting universe, wedged against other neutrinos like so many subatomic sardines, one hundred of you crowding every cubic centimeter of space. Under such circumstances, you and your comrades could form a new state of matter called a neutrino condensate
, Alexander hypothesizes. This would act something like a superfluid—a fluid that doesnít lose energy to friction. (If you stirred some superfluid creamer into your superfluid coffee, it would just keep swirling around the mug, never settling down.)
Two types of physics—
neutrinos and dark energy
—appear to be built
from the same bedrock.
- Stephon Alexander
Itís a nice plot twist, but what does it have to do with the universe that we see around us? The answer is that a compressed neutrino condensate could produce some very familiar effects that as yet have no explanation. Energy from the condensed neutrinos would set the universe expanding—fast. Cosmologists already believe that soon after the Big Bang, the universe went through a short period of rapid expansion, known as "inflation
," but they have not been able to figure out why it occurred. Now, with the help of a $65,000 grant from FQXi and colleagues at Penn State University and Haverford, Alexander is investigating whether the humble neutrino holds the key.
A bouncing universe is only one possibility for how a neutrino condensate might form. Another is based on the notion that a collapsing star could squeeze neutrinos into a condensate, on its way to becoming a black hole. In that case, our universe might actually have formed in the neutrino soup housed inside a black hole.
A universe in a black hole may seem like an outlandish idea, but if correct, we still live within a neutrino condensate, which could be causing the expansion of the universe to accelerate. Astronomers have observed such an acceleration, and usually attribute it to some mysterious ďdark energy
A strange parallel between neutrinos and dark energy gives Alexander a hint that heís on the right trail. Neutrinos come in three flavors
, and they are able to flip, or oscillate, between them. Think of the neutrino as the ultimate dish of Neapolitan ice cream, which spontaneously transforms from vanilla to strawberry to chocolate and back again. Surprisingly, the frequency at which neutrinos flip from one flavor to the next seems to be linked to the density of dark energy in our universe.
The Sudbury Neutrino Observatory
(pictured) found that neutrinos
oscillate between three flavors.
"This is very surprising," says Alexander. "Two different types of physics that should have nothing to do with each other" appear to be built on the same bedrock. Yet physicists still do not understand why neutrinos oscillate. Could it be that the flavor-flipping is the direct result of traveling through a neutrino condensate? "A neutrino moves in that medium like a boat moving in water," explains Alexander. Perhaps neutrino oscillation is like that boat bouncing on the waves.
at the University of Illinois at Urbana-Champaign, an expert on what happens when exotic materials are squeezed down into new states of matter, finds the idea "truly novel." "Alexander has combined ideas from my field of condensed matter and put them to use in his own," he says.
While condensed matter physicists have produced examples of superfluids and condensates of other types of exotic matter, Alexanderís neutrino condensate cannot be cooked up in the lab because neutrinos are too slippery to capture and bundle together. But Alexander hopes to make testable predictions based on his theory that link the characteristics of neutrinos to the observed properties of dark energy. "We can use the universe as a laboratory to test particle physics," he says.
, a theoretical physicist at the Perimeter Institute in Ontario, is a fan of Alexanderís original thinking. "He has a very fertile creativity combined with an independence of mind," he says.
So will neutrino condensation turn out to be the right answer to these cosmic riddles? Perhaps. As Smolin puts it, "We donít know if it is true, but it is something that, so far as we know, might be true."
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As for the Black Hole Universe it might be useful to see the following article