Steven Hawking, Super-force and String theory

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Steven Hawking, Super-force and String theory

#1  Postby Mick » Sep 11, 2011 11:10 pm

I was watching a documentary on Steven Hawking. He was talking about the limitations of his view on things, in particular an explanation of why gravity is (or appears to be) weaker than the rest of the forces (which together with gravity supposedly made up a super-force...or something?). He then said that string theory, though largely unproven, has an answer to this which involves there being many ten or even eleven dimensions.

Okay, some questions.

(1) Was this super-force the only 'thing' which existed? Was there something else?

(2) What does it mean to state that the theory unifies "gravity with the other three interactions"? What sense of unity are we talking about here? Was it a single force? So it'd be that gravity as we know it today did not 'always' exist (it is now distinct after all, isn't it?)

(3) My brain turns to mush when I try to think that there are eleven dimensions. Is there are way to understand this which is not so hard to swallow?
Christ said, "I am the Truth"; he did not say "I am the custom." -- St. Toribio
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Re: Steven Hawking, Super-force and String theory

#2  Postby newolder » Sep 14, 2011 9:41 am

re 3: swallow the linked and bite-sized chunks @ ur leisure: http://www.dimensions-math.org/
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Re: Steven Hawking, Super-force and String theory

#3  Postby Evolving » Sep 14, 2011 9:52 am

re (2), from one of my textbooks (my favourite recourse when I'm not sure how to explain something...):

It is suspected that all four interactions may be different manifestations of a single fundamental type of interaction. The reason for such a belief is partly philosophical and partly experimental. The ‘philosophical’ justification for the unification of interactions is that this type of approach – reducing the physical world to what appears to be the minimum number of particles and processes – has been outstandingly successful, and physicists see this as the next logical advance. If this sounds wildly idealistic, then the ‘experimental’ justification should offer some reassurance. A key idea in demonstrating that two interactions are linked is that under certain physical conditions they should behave in the same way. So, for instance, the strength of two interactions may become the same. Experiments using particle accelerators have revealed that the strength of interactions depends on the interaction energy. In particular, the strengths of the electromagnetic and weak interactions are observed to become closer to one another at high interaction energies. At interaction energies of about 1000 GeV, the strengths of these two interactions are predicted to be the same, and the electromagnetic and weak interactions should appear as different manifestations of a single underlying electroweak interaction. It is believed that the unification of the other interactions occurs at very much higher interaction energies. The unification of the strong interaction with the electroweak interaction – which is termed ‘grand unification’ is predicted to occur at an interaction energy of about 10^15 GeV. The theoretical framework that is used to describe this unified interaction is called a grand unified theory or GUT.

The energy at which the gravitational interaction might become unified with the other interactions, if such a thing happens at all, is expected to be higher still – about 10^19 GeV. At such extreme interaction energies the gravitational interaction might become important for interactions between particles (at lower energies, the gravitational interaction has a negligible effect on particle interactions). In terms of the evolution of the Universe, an interaction energy of 10^19 GeV corresponds to the Planck time (~ 10^-43 s). As has already been mentioned, there is no accepted ‘theory of everything’ which allows the processes that occurred in this Planck era to be understood. The interaction energies associated with GUT interactions and the Planck era are extreme – there is probably no environment in the present-day Universe in which particles interact with such energy. Thus, it is unlikely that direct experimental verification will ever be made of theories that describe interactions at such high energies.

The expected behaviour of the fundamental interactions over the first few moments of the history of the Universe can be summarized as follows. Prior to t ~ 10^-43 s all four fundamental interactions may have been unified. After this time, the gravitational interaction became distinct from the GUT interaction. Some time later, at t ~ 10^-36 s the strong interaction and the electroweak interaction became distinct from one another. Finally, at t ~ 10^12 s, when the typical interaction was about 1000 GeV, the weak and electromagnetic interactions took on the form in which they act in the present-day Universe.
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Re: Steven Hawking, Super-force and String theory

#4  Postby Ihavenofingerprints » Sep 14, 2011 10:05 am

:popcorn: Looking forward to answers. I'm not very sure, but in regards to (1)... I was reading this today: http://en.wikipedia.org/wiki/Timeline_o ... anck_epoch (maybe this is what he was referring too?)
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Re: Steven Hawking, Super-force and String theory

#5  Postby Evolving » Sep 14, 2011 10:22 am

Ihavenofingerprints wrote::popcorn: Looking forward to answers. I'm not very sure, but in regards to (1)... I was reading this today: http://en.wikipedia.org/wiki/Timeline_o ... anck_epoch (maybe this is what he was referring too?)


Yes - the first three "epochs" described there are the times described in the excerpt that I reproduced in my post. The idea is that initially (during an unimaginably short period of time) there was only one kind of interaction, and that fragmented, in three steps, into the four interactions we know today, over the course of a trillionth of a second, as the average interaction energy decreased.
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Re: Steven Hawking, Super-force and String theory

#6  Postby Evolving » Sep 14, 2011 2:00 pm

...oh, and re (1) in the OP: this single unified interaction was certainly not the only "thing" which existed: there was a universe of things, albeit in a comparatively confined space; but these things interacted with each other (it is suggested) in one way only.
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