Professor Brian Greene answers everything you wanted to know about string theory and the multiverse

Professor Brian Greene answers everything you wanted to know about string theory and the multiverse

Lateline asked you to send in science questions for famed physicist Professor Brian Greene.
Professor Greene is the author of The Elegant Universe, a Peabody Award winner, and director of Colombia's Institute for Strings, Cosmology and Astroparticle Physics.
He spoke to Lateline about the multiverse, string theory and what could be out there.
In case you are wondering, string theory is the idea that the fundamental element of all matter and the forces of nature are even tinier than the smallest particle, and are in fact vibrating filaments of energy of different shapes and sizes that look like strings.
These strings use different vibrations to ultimately create both the chaos of sub-atomic matter and the smoothness of interstellar gravity waves.
Here is what you asked and Professor Greene's answers:

Time in parallel universes?

Bruce Cornell: Professor Greene, you say that in parallel universes there may be more or less dimensions than in ours. Is it obligatory that in parallel universes, time be one of those dimensions?
Professor Greene: It's a great question and again, we are talking hypothetical here. We do not know whether there are extra dimensions or multiverse. Let's go forward with the possible ideas that come out of the mathematics. It's hard for us to imagine a universe that would have no time at all. Time allows change to take place and the very evolution of the universe is what requires some conception of time. Mathematically can we write down a universe that doesn't have time? Sure. Do we think that would be realised in the larger reality that is out there? None of us take that possibility seriously.

Something from nothing?

David Richardson: If there was a beginning, how did something (the universe or the multiverse) come from nothing?
Professor Greene: I have absolutely no idea and nor does anybody else on the face of planet Earth. So again that's one of those great questions at the cutting edge. We do have ideas, suggestions, possibilities — for instance it could be that the state of nothingness is unstable. That is, you can have nothingness, absolute nothingness for maybe a tiny fraction of a second, if a second can be defined in that arena, but then it falls apart into a something and an anti-something. And that something is then what we call the universe. But can we really understand that or put rigorous mathematics or testable experiments against that? Not yet. So one of the big holy grail of physics is to understand why there is something rather than nothing.

The practical applications of gravitational waves?

Bevan John Kirkland: Does Brian believe that the recent discovery of gravitational waves will have practical applications to benefit humankind? If yes, can Brian list the applications?
Professor Greene: Well it depends what you mean by practical applications. If you mean building some new iPhone or widget or something, no, I don't think so. But if you think about a practical implication of enriching your life and giving you a sense of being part of a larger cosmos and possibly being able to use this as a tool in the future maybe to listen not just to black holes colliding, but maybe listen to the big bang itself, those kind of applications may happen in the not too distant future.

The song of the universe?

Ivan de Vulder: If string theory is about vibrations having differing effects on the environment, so too do sound waves. One of the most profound effects on us via sound waves is music. With this in mind, what do you think the universe (string theory) song sounds like?
Professor Greene: Well I wish I could hum it for you. In essence, we string theorists have been trying to work out the score of the universe, the harmonies of the universe, the mathematical vibrations that the strings would play. So musical metaphors have been with us in science since the beginning. The beauty of string theory is the metaphor kind of really comes very close to the reality. The strings of string theory are vibrating the particles, vibrating the forces of nature into existence, those vibrations are sort of like musical notes. So string theory, if it's correct, would be playing out the score of the universe.

What about alien life?

Macy Percival: Does Brian Green believe there is another planet like Earth somewhere in the universe where life as we know it has or is evolving?
Professor Greene: Obviously nobody knows the answer to that so it's just wild speculation, but if you asked me to speak form my gut, my intuition, yeah I think so. So many galaxies, so many planets out there in the universe circling so many stars... it just feels like there's a very good chance that there is another Earth-like planet out there that is able to support some kind of life similar to what we're familiar with. So my guess would be yes.

Bonus Question

Dr Karl Kruszelnicki: Both General Relativity and Quantum Mechanics are perfectly valid ways of exploring our understanding of the universe around us. They both work really well. But they are built on completely different assumptions. In Quantum Mechanics there is no real causality but in General Relativity there is. In Quantum Mechanics, time and space are fixed, but in General Relativity they are as flexible as rubber, a kind of "timey-wimey" Doctor Who insubstantial mess. How can these two systems work on completely opposing bases?
Professor Greene: In quantum mechanics there is A causing B. The equations do not stand outside that usual paradigm of physics. The real issue is that the kinds of things you predict in quantum mechanics are different from the kinds of things you predict using general relativity. Quantum mechanics, that big, new, spectacular remarkable idea is that you only predict probabilities, the likelihood of one outcome or another. That's the new idea. General relativity is in the old Newtonian framework where you predict what will happen, not the probability of what will happen. And putting together the probabilities of quantum mechanics with the certainty of general relativity, that's been the big challenge and that's why we have been excited about string theory, as it's one of the only approaches that can put it together.


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