Physicist Explains The Full Implications Of The Just-Released Evidence For How The Universe Began
The B-mode polarization was detected in the cosmic microwave background radiation.
Physicist Randol Aikin was part of a team of researchers who on Monday announced they had found direct evidence that supports Inflation Theory, the 30-year-old idea that the universe expanded faster than the speed of light in the microseconds after it was born.
After the announcement, Aikin particiated in an "Ask Me Anything" on Reddit, providing a clear explanation of the discovery and what it means for our understanding of the early universe.
Dr. Randol Aikin
"Inflation explains the 'Bang' in the Big Bang," Aikin writes. "Don't think of an explosion. Instead think of something rapidly expanding. I like to think of some hot white point expanding — doubling in size over and over and over again. And finally when it's done, the universe is filled with hydrogen and helium and all the stuff that will one day become planets, stars, and galaxies. Our discovery yesterday tells us, for subtle reasons, that inflation theory — this radical picture — is actually right."
The BICEP2 team, short for Background Imaging of Cosmic Extragalactic Polarization, used a telescope at the South Pole to observe light that comes from when the universe was only about 400,000 years old. The researchers were looking for a signal that changed the pattern of that light very early on. The signal came in the form of radiation patterns, which researchers believe are marks left by gravitational waves created during the rapid period of expansion, or inflation.
Here are some more highlights from the Reddit thread:
On designing the BICEP2 experiment:
We began designing the experiment in 2006. We sent the telescope to the South Pole in 2009, took data until 2012, and published yesterday. The wider BICEP2 team consists of lots of folks — more than 20, less than 40 or so. We go to the South Pole because the atmosphere is thin and dry — perfect for observing the microwave radiation we're after.
On what preceded the Big Bang:
To give a bit more of a complete answer, folks that work in this field in general skirt questions about "before" the Big Bang. In part, this is because different people mean different things when they say "Big Bang." Some people consider the process of inflation (a period of rapid expansion in the early universe) is itself the big bang. Others will tell you that the big bang is the thing that gave rise to inflation. Our discovery will absolutely help us understand the process of inflation and what gave rise to inflation.
No one quite knows what preceded the big bang... We're still waiting on a complete theory that describes the physics at the highest energy scales. So turns out that energy and matter are interchangeable. During the process of inflation and subsequent expansion, different particles "freeze out," meaning the energy gets low enough that the particles, colloquially speaking, crystallize into existence.
On the meaning of inflation:
What we generally consider to be the "universe" is the stuff that we can actually see and observe. We generally call this stuff "causally connected." Inflation theory tells us that before inflation began, the universe (the stuff we're causally connected to) was big. Then the universe expanded. A LOT. At the end of inflation, the region of the universe that was causally connected was tiny compared to before inflation.
On gravity waves:
This is not a direct detection of gravity waves. We'll leave that to the folks working on the LIGO experiment. Instead, we see the indirect effects of gravity waves. The polarization of the light from the cosmic microwave background is generated by hot and cold patches in the early universe. The gravity waves change the hot and cold patches, so they change the polarization pattern that we observe. If you want a more complete explanation, Google "Wayne Hu cosmology." He gives a really thorough explanation.
On quantum gravity:
So far, no one has really been able to put together a complete and convincing framework for combining quantum mechanics and gravity. Our discovery tells us that quantum gravity is a real thing.
Inflation is a process that stretches the universe by many, many orders of magnitude, right? So that means that very small scales (quantum scales) get stretched to astrophysical scales. We have found evidence of the effects of gravitational waves at astrophysical scales around 400,000 years after the big bang. Theory tells us that these gravitational waves must have been created at the quantum scale and stretched by inflation (the theoretical reasons for that are somewhat complicated). The fact that we see the effects of these things tells us that there must have been quantum fluctuations in the gravitational field before inflation. In other words, quantum gravity.
On the moment of discovery:
There was no one single moment. You first assume that the signal is not real and you've done something horribly wrong. Then over time, you get closer and closer to convincing yourself that you haven't screwed up and you've actually discovered something real!
On confirming the findings:
The great part about this experiment is that a bunch of really smart theorists were able to tell us what the signal should look like. We go out (to the south Pole) and measure the thing, and we actually see what the theory predicts! If you want a more technical answer, it's that the B-mode isn't a signal so much as a signature. It's a particular pattern of the polarization of the light from the early universe.
On dark energy:
There is a lot in common with dark energy and inflation and they lead to strikingly similar evolutionary mechanics. There is still no commonly accepted theory for a firm connection between the two, but many of us have a hunch that they must be connected... If nothing else, the theoretical framework for describing one will certainly help understand the other.
On dark matter:
I think it's safe to say that this discovery does not have any direct implications for explaining what the dark matter is. While inflationary expansion stopped long ago (just a fraction of an instant after the big bang), the universe itself is still expanding. Whether there is a connection between inflation and the dark energy that's driving the current expansion of the universe remains to be seen.
On the observable universe:
So at risk of sounding like a total... not sure what... I'd say that the "edge" of the universe is in some sense time. The size of the universe — the stuff to which we are "causally connected" (meaning the stuff that we can see, essentially) grows with time. This is because light takes a finite amount of time to travel. So the longer we wait, the further it travels. In that sense the "edge" in some sense is traveling outwards.
Skepticism is absolutely warranted! We count on our competitors to get out there and to try to prove us wrong. That's the beauty of science. I hope these folks read the papers carefully.
On the next major physics discovery:
Direct detection of the dark matter. The current prevailing theory is that dark matter is made up of WIMPs — weakly interacting massive particles. I think scientists are very close to actually measuring one of these things and setting a cross section. That would be HUGE.
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