One of the explanations as to why gravity is 10^42 times weaker than electromagnetism is because gravity travels outside our 4-D space and enters the 11-D reality and its energy is spread out.
However if that were true and (assuming) there are parallel universes giving off their own gravity, why aren’t we getting tons of gravity energy from them? If 99.9999999…etc% of the energy from gravity leaves our reality, it has to enter somewhere else so why doesn’t ‘their’ gravity energy enter our reality too? Why don’t we have people walking around on the street and suddenly experience a strong gravity force that comes out of nowhere and pushes them straight to the ground? Do we get weird gravity readings, or gravity that comes out of nowhere? The only thing I can think of are things like the mystery hole phenomena where in some areas gravity doesn’t work properly and you can lean sideways and not fall down. But who knows what causes that.
First, there is no evidence that gravity leaves our reality, even if parallel universes do exist.
And if there are more than four dimensions, the extra dimensions are just as much part of our universe as Cleveland. Gravity does not in any way travel “outside our 4-D space and enters the 11-D reality” The 11-D reality is our universe. We may not see the other dimensions, but we don’t really see time either.
I read the article. It says exactly what I said earlier, that gravity may propagate through all eleven dimensions of our universe.
This hypothesis - hypothesis because it is potentially testable, but no experimental evidence for it yet exists - has been part of string theory for a very long time. The only new idea I see in that article is another hypothesis - that this well-known notion may also explain the expansion of the universe. But that’s our universe, not a different one.
It’s unfortunate that the word “leaks” is used, because it’s simply wrong. But it is a popular article for an audience of laypeople and the word gives a colorful impression of what’s really going on. Obviously it’s confusing, though,
I believe this is a relatively new theory, or at least one that has attracted slightly more attention recently. If these were the traditional “curled-up” extra dimensions of string theory, they would make no difference to the strength of gravity over macroscopic distances because the entire extent of the dimensions would quickly become uniformly saturated with force-carriers (They could well make a difference over microscopic distances. This has expired recent experiments which have not found positive results.). These hypothetical space dimensions are those of a larger space in which our universe is hypothesized to be embedded like a line or a plane in ordinary 3-D space.
As for where the gravity goes, if this theory were correct—I think we really wouldn’t be able to say. It would go outside the realm we know how to observe—outside what we normally think of as our universe. I think the most economical guess, and the simplest explanation for why we haven’t noticed any extra gravity coming in from outside, is that this external space is completely empty—empty even of most or all of the quantum fields that allow forces and matter to exist here. It’s conceivable that there could be other universes akin to or different from ours floating “out there” somewhere, but we have very little basis on which to speculate.
To the best of my knowledge, this theory isn’t generally taken all that seriously. There’s no direct evidence for any extra dimensions, and most physicists prefer to explain cosmological acceleration along more “conventional” lines as an effect of ordinary Einsteinian gravity from some sort of negative-pressure field.
Matter in adjacent branes is also sometimes called upon to resolve the dark matter problem. There is definitely something which is causing gravitational effects in our Universe which we cannot see. You don’t just get sudden forces out of nowhere from the dark matter (whatever it is) for the same reason that you don’t get sudden forces out of nowhere from ordinary matter. If a chunk of matter approaches us in normal space, the gravitational effects from it gradually increase as it gets closer, and the same would be true of a chunk of matter on another brane, if gravity does indeed cross branes. Even if something did get very close, it probably wouldn’t knock you off your feet, since it’d effect the Earth in the same way that it does you.
Well, it’s okay, 'cause they’re all rolled up into little tiny tubes that are smaller than can be physically resolved, i.e. smaller in “diameter” than a Planck length.
Or something. :dubious:
Seriously, M-Theory, or Brane theory, or string/twistor/whatever theory is just a mathematical treatment with zero experiemental or observational verification. 'Course, the same thing was true about quantum mechanics waybackwhen, but QM and its children have been pretty extensively validated in the intervening decades. Any explaination based upon M-Theory and the existance of branes or compactified extra dimensions should be taken as no more than speculation at this point.
But it is a neat toy to play with, and who knows: it might just be right, or partially right. But don’t go investing in any “supersymmetry” start-ups.
This suggests some interesting possibilities for the tinfoil-hat crowd. What if the reason we haven’t seen the death star (nemesis), or planet X, or Nibaru, or whatever other names it goes by, is that it exists in a solar system of another brane which is gravitationally coupled to our solar system? The planets could be pulled from their orbits by these things, and we’d never see them coming! :eek:
Now, don’t go encouraging them. They get quite enough from the Fox network as it is.
Ummm…this seems pretty unlikely to me (though I’ll admit that I’m not really up on brane theory, such as it is.) Dramatic and localized gravitational effects like that would be readily apparent via unexplainable irregularities in the orbit of planets and comets. The effect that this theory is trying to explain is the apparent weakening or some other kind of repulsion over long (“cosmic”) distances, which allows for the recently discovered accelerating expansion of the universe and possible variation in the rate of (or rate of change of) expansion over time.
But, to continue with the tin-foil hat idea, we’d be able to “see” these other planets the same way we “see” other cool dense matter or singularities…by their gravitational lensing and effect on other masses. Still, you should be able to get funding for a special on the Sci-Fi Network…if they can wedge it in between the “The Secret KGB UFO Abduction Files” and “Crossing Over with John Edward”. :rolleyes:
Perhaps you can get it sponsored by Reynolds’ Foil: “Stops 30% More Government Mind-Control Rays Than The Leading Brand! When It Comes To Protection, Choose Genuine Reynolds Aluminum Foil!”
Out of curiosity what do you do for a living? From what i’ve seen on these boards you remind me of the stereotypical mathematical genius with poor social skills (no offense). Are you involved in physics in anyway?
is theory is just a theory, but I don’t know much about this subject other than what is covered on PBS. But if the theory were true why wouldn’t we be getting weird gravity readings from other 4-D universes?
Well, I don’t know about the genius part, but I think you hit everything else pretty much dead-center.
I’m have a degree in mechanical engineering with minors in physics and mathematics. (The math minor is purely incidental; a result of taking all the math I was going to need for a physics major plus a couple of computer science courses. I am not a mathematician by any stretch of the imagination.) I currently work in the aerospace field (one of those companies named after some pasty-faced dead guys with slide rules on their belts) and in the past worked in off-road handling and construction equipment, with brief excursions into automotive and consumer products.
I’m not conversant with brane theory, which has emerged into the cosmology “mainstream” only in the last few years (or, at least I wasn’t aware of it before then) but my vague, probably incorrect understanding is the interactions between branes are “weak” on small time and length scales, and are only manifested in cosmological-size structures. So, we wouldn’t notice them until we start looking at distant structures and noticing that gravity isn’t operating as strongly as current theory would suggest, which is, in fact, what we see. Whether the proposed mechanism in M-Theory is correct is a horse of another visual scheme entirely.
I don’t mean to poo-poo it as being worthless, or definitely wrong–it certainly isn’t any more wrong at this point than any other theory put out there, including the Great Green Arkleseizure theory–but one gets the impression from reading about it in the popular press as being a validated theory that is just undergoing refinement, when in fact is it bald-arse speculation and even among proponents of the various theories that fall under the moniker of “superstring” theories (branes, M-Theory, twister-enhanced string theory, cosmological spaghetti theory*) there are major disagreements on how they work, how many dimensions they require and where the extra dimensions are hidden, what the cosmological implications are, et cetera. It is, in fact, just a mathematical model that happens to map the functions of the observable world by virtue of the fact that it is designed and tweaked to do just that. There is not, to my knowledge, any incidence where a new phenomenon or particle has been predicted by string theory, and until that happens it is better termed a hypothesis. I suspect it’ll end up being thrown in the same conceptual junkpile as the four bodily humours or the luminiferous aether, but one never knows; it may have the threads of the actual mechanisms underlying the seemingly ontologically arbitrary rules of the physics on the quantum scale.
Okay, I made that one up. But it fooled you for a second, didn’t it?