Physics

One Big Question: What laws of quantum mechanics could have made the Big Bang a Big Bounce instead?

One Big Question: What laws of...
Dr. Gielen (left) and his partner on the paper, Neil Turok of the Perimeter Institute for Theoretical Physics
Dr. Gielen (left) and his partner on the paper, Neil Turok of the Perimeter Institute for Theoretical Physics
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Dr. Gielen (left) and his partner on the paper, Neil Turok of the Perimeter Institute for Theoretical Physics
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Dr. Gielen (left) and his partner on the paper, Neil Turok of the Perimeter Institute for Theoretical Physics

We recently reported on a theory that says our universe might not have gotten its start when it collapsed in on itself and exploded. The theory says that such an event may have been prevented by the laws of quantum mechanics, meaning that the beginning of our current universe would have been more of a Big Bounce than a Big Bang.

As the next installment of our regular feature called "One Big Question", we asked theoretical physicist Steffen Gielen from Imperial College London exactly what laws of quantum mechanics would have come into play to make the Big Bounce theory tenable. Gielen is one of the authors of a paper detailing the concept. Here's what he had to say.

One of the main properties of quantum mechanics is that it allows processes that are impossible in classical physics. In particular, there is a phenomenon known as quantum tunneling, of which a good example is radioactive decay. Normally, the attractive nuclear forces hold the nucleus together and nothing can escape. But in radioactive decay, every now and then the "forbidden" process in which a part of the nucleus escapes the nuclear force does occur. Now you can ask the question, "how did the particle do that and escape these forces which look too strong to be overcome?"

It turns out that mathematically, the most accurate description for this "tunneling" process is given by using complex numbers. In a precise mathematical sense, one can say that the particle went through the attractive forces by "escaping" into complex time, rather than following along its usual real time. When time becomes complex, attractive becomes repulsive, allowing the particle to escape.

In our work, the universe pretty much does the same.

Normally one would expect it to collapse onto itself until it reaches a point of infinite density, the "Big Crunch," which would then become the Big Bang when seen from the other side, where the universe expands again. In terms of cosmological "time", one would describe this as a process where the universe contracts, hits the Big Crunch/Big Bang at time zero, and then expands as time ticks along.

Now when we use quantum mechanics, we find that a different evolution is possible, in which the universe does not have to go through time zero, but instead goes into complex time, around the singularity at zero. The complex numbers basically give a second dimension to time that the universe can explore, so that the Big Crunch/Big Bang can be avoided entirely. This may sound like a cheat, but as I said is pretty much exactly what happens in real-life situations such as radioactive decay, which can only be understood in quantum mechanics and using complex numbers.

8 comments
GregSmith5a5d6b514f8a4f66
"Escaping" into complex time - like into another dimension?
Ken Brody
So, the probability density of the Big Bang had a complex component and therefore it had a wave component "outside" of the universe? Wow! I assume the same would be true for the singularity in a black hole. There would be a probability it could escape beyond it's own event horizon?
JuliusMazzarella
Does the inflationary model of the universe require a big bank or big bounce? The problem with the description "big bounce" is you don't know if the author is suggesting a cyclical universe. This I believe is an entirely different theory than inflationary cosmology or is the author saying the universe bounced just once? I think Stominger is the big bounce theorist and Guth the Big Bang. In any event the author owes it to the reading community to clarify these two issues with the article.
Expanded Viewpoint
I can hardly believe that so many "scientists" still put any stock at all in the BBT, since it was pretty well laid to rest as false back in the early 1970s. An astronomer was doing spectrographic analyses of thousands of stars from the 1950s until the 1970s, and he couldn't come up with even just two that had spectral lines that were even close to being the same!! TWENTY YEARS spent looking and looking and looking some more, and he finally called it quits. Ergo, no "big bang" occurred. If such an event did take place, we would see LOTS of homogeneity throughout the galaxy, but yet, we do not. According to this guy, of the many thousands of stars he examined for their spectral signature, they were as different as snowflakes. Also, from WHERE would all of this material have come from to have a sudden expansion (BB) anyway? Was there a precursor "bang" of sorts that generated the source of all the matter we have all around us? And if that's the case, from where did that stuff come from? It makes no sense at all when looked at from a logical point of view. And where does space begin and end? What's on the other side of the "wall"?
ClarkMagnuson
Paul Steinhardt and Neil Turok or Roger Penrose are all good on this topic. Find them on youtube.
apprenticeearthwiz
I know of no specific research to determine whether our universe is biological or not. In the absence of any such research our current view of the cosmos as entropic, therefore non-biological, is an unexamined assumption. A massive potential for GIGO.
neutrino23
I don't have the ability to judge their argument. There are a number of competing theories for the beginning of the universe. I think the Big Bang Theory is not in dispute. The question is if something came before that. If you read Krause (A Universe from Nothing) he presents the school of thought that the universe spontaneously arose out of nothing. If you add up all of the energy and quantum numbers in the universe this group claims that the result is zero. They also cite recent work that shows the universe will expand forever. The string theory people, if I understand them (I don't understand any of this very well), have the idea that nothing can be less than the size of the Planck length. A previous universe would have collapsed to this size and then expanded again. All of these are mathematical models that try to fit our observations. Kudos to these researchers.
Bob
That everything was created from nothing was written over 4,000 years ago.