Escaping to other dimensions....

[Stunster]

"Escaping to other dimensions", I don't know, where will it all end...?


Leaking Gravity May Explain Cosmic Puzzle

1 hour, 1 minute ago

Science - Space.com

Sara Goudarzi
Special to SPACE.com
SPACE.com

WASHINGTON, D.C. - Scientists may not have to go over to the dark side
to explain the fate of the universe.

The theory that the accelerated expansion of the universe is caused by
mysterious "dark energy" is being challenged by New York University
physicist Georgi Dvali. He thinks there's just a gravity leak.

<snip>

Dvali borrows from string theory, which states that there are extra,
hidden dimensions beyond the four we are familiar with: three
directions and time. String theory suggests that gravitons --
hypothetical elementary particles transmitting gravitational forces --
can escape to other dimensions. Dvali says this would cause "leaks" in
gravity over cosmic proportions, reducing gravitational pull at larger
distances more than expected.

<snip>

http://story.news.yahoo.com/news?tmpl=story&u=/space/20050228/sc_space/leakinggravitymayexplaincosmicpuzzle

I have two questions

1) Gravitons are quanta of gravitational energy; and E = mc^2; so, if gravitational energy can escape our familiar spatial dimensions, shouldn't it also be possible in principle for mass to escape our familiar spatial dimensions?

2) What about the Conservation of Energy?

[Wilms]

1. Kick for answers. n/t

[AZCat]

2. What about conservation of energy concerns you?

Please elaborate...

[Stunster]

3. What concerns me is that

I thought it was a fundamental principle of physics.

This theory suggests that perhaps it isn't, because gravitational energy on this theory might leak from the universe.

If true, that would be quite something, no?

[AZCat]

4. Your "system" isn't large enough

Conservation of energy is about the transfer of energy within a system; it is not about energy transfer across a system boundary.

In order to apply conservation of energy principles, you would have to enlarge your system to include whatever space the gravitational energy is leaking to.

[Stunster]

5. Systems and system boundaries

I guess what I'm asking is how does one define the boundaries of the system.

Let's say there are other universes. What makes them other universes, and not just part of this universe?

Now, I'd have to have the details of Dvali's theory explained to me, but suppose that it or another theory does involve the postulation of other universes. And suppose other universes can be permitted by the theory to have different laws of physics.

My question, then, is this:

Is gravitational leaking between universes a coherent notion, or does the fact of such leakage simply mean by definition that we're not talking about different universes at all (but rather merely different dimensions of this universe)?

Or to put it more generally, what degree of causal closedness is required for something to qualify as a universe?

It strikes me that the kind of theorizing going on among some string physicists is such as to suggest that being a 'causally closed system' is perhaps not a well defined notion.

Gravitational leakage suggests that we could affect what happens in another region of space. But for that effect to occur, it would seem that there must be a spatial channel between our region and the affected region. But if there is such a channel, then we normally think that we could send a physical probe to that other region. But it seems that there might be some reason of principle why a probe cannot reach a dimension or region of space or other universe governed by different physics from our region of space. What would happen to a physical probe in region R governed by laws L if an attempt was made to send it to region R* governed by laws L*?

So if we can't send such a probe from R to R*, but if gravitational energy can leak from R to R*, then there seems to be an ambiguity in the notion of the causal closedness of a spatio-temporal system.

[sans qualia]

6. The latter

the fact of such leakage simply mean by definition that we're not talking about different universes at all (but rather merely different dimensions of this universe)

I think you pretty much hit the nail on the head. For any event x in system A, for any event y in system B, if a causal correlation exists between x and y, then neither A nor B is a closed system. I think. A universe, by definition, is a closed system. If indeed there exist dimensions of space beyond the three with which we are immediately familiar, then any "extra" four-dimensional spacetime continua within them do not constitute "universes" per se.

Eeeh... gibberish. Nevermind.

[On the Road]

7. Gravitons Might Have Unique Properties

that allow them to leak where other particles can't.

String theory proposes other spatial dimensions, but they are believed to be "rolled up," making them too small (smaller than the Planck length) to have much effect on normal matter.

Gravity is different from other energy in some fundamental ways. This could be one of them.

[phantom power]

8. When it comes to gravity,

Some "non-graviton" models appeal to me. Gravity appears to behave rather differently than other forces, and it seems reasonable to consider that it might simply arise from a different phenomenology.

http://www.calphysics.org/haisch/sciences.html


That, or a graph-automata model, where gravity, relativity, etc are also somewhat separate from other particle-based forces.
http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:physics/9902034

[On the Road]

9. Yes, I'm Not Particularly Sold on Gravity Particles

but other forces appear to exist both as waves and particles. It would be natural to assume that gravity also does.

The articles you cite are interesting, and may even turn out to be true, but they're currently not the mainstream view.