Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum The multiverse and extra dimensions.

Yes, it is - and being stationary in that field means you're accelerating away, but not moving away, from it.


If acceleration away from the field is increased, so that you're moving away from it, then yes.

This might help clarify it:

"Einstein came to realize the principle of equivalence, and it states that an accelerated system is completely physically equivalent to a system inside a gravitational field."

Read more: http://www.dummies.com/how-to/content/ei...l#ixzz12kuVknwK

Consider this: as we sit at our computers we're being accelerated away from Earth's gravitational field at 9.81m/s2, thanks to the nuclear forces beneath our backsides. Despite the fact that it's not getting us anywhere fast, it is, in General Relativity, acceleration, and we experience it in exactly the same way as we would if we were accelerating at the same rate aboard a spacecraft far from any g.f.

What it boils down to is: According to G.R. if you're not in free-fall, then you're accelerating. Conversely, if you are in free-fall, then you're not accelerating.

Thanks. I think I got my head round the equivalence thing a while ago - sort of. I see now that I had just misinterpreted the original quote as saying that sitting still in a G F and accelerating away from that same position were exactly the same.
Qualitatively, they are the same, but not quantitatively; right?

Yes. At least, I think so; since we're not mathematical physicists we're bedeviled by the ambiguities of ordinary language - which was the cause of the foregoing misinterpretation.

Earlier we were looking at whether or not gravity was a force. You made a comparison:
The difference here seems to be that whereas scientists agree that there is a duality in the case of wave/particles, the same author can say categorically that gravity is not a force, then treat it as if it were.

You're right of course. It's probably because it's a lot simpler to understand, explain, and work with Newtonian physics, and there's most often no need to resort to G.R.Theory in order to obtain sufficiently accurate results. It's understandable, unless the aim is to teach G.R, but it would help the uninitiated if that were at least made clear at the outset.

When I think about gravity I find I keep coming to the question: If it is not a force, but just the result of a distortion of spacetime, would there not have to be a force that distorted spacetime, and maintained the distortion? If so, what is that force, and where does its energy come from?

In another thread we, sort of, traced this back to the Big Bang, but if that line of reasoning is right it seems no more than a semantic nicety to say that gravity is not a force, but a force is required to create and maintain it.

I have just found the other thread in which we came to this point.
Your quote from Wilczk:


Although relevant, this does assume the presence of gravity, without accounting for its presence. Massive objects can be created from energy, but you have to add gravity to "construct heavy objects".

Returning to our earlier exchanges about rolled-up dimensions, I found a quote from Amanda Gefter (New Scientist,14.07.2007. Pp30-34)regarding the extra dimensions of string theory: “To have gone unnoticed all this time, these dimensions must be curled up like submicroscopic origami. What’s more, the number of forms that this origami can take is truly vast, with each one corresponding to a different universe with different particles and different fundamental constants.”

What Gefter seems to be saying here is that the other universes exist within the curled up extra dimensions. Obviously, we have to consider the possibility that they may be rolled up only in our F of R. Perhaps “rolledupness” is relative. A dimension that is rolled up in the F of R of one observer could be fully extended in the F of R of another.

Could this throw some light on the question as to why it seems necessary for extra dimensions to be rolled up to an infinitesimal degree so that we cannot detect them, whereas alternative universes can apparently permeate our Universe, yet remain undetectable?

We must consider the possibility that all the other universes intermesh with ours because they exist within dimensions that are tightly rolled up in our F of R, but expanded in their own. Such a concept would necessarily imply that our Universe is present in all these other universes in the same way. In their frames of reference we are “submicroscopic origami”.

I can see this becoming quite complicated!