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sirjon
2009-Jul-31, 08:33 AM
I am just curious. General relativity suggested that space is not really flat but actually curved or warped by the presence of matter and energy on it. It also suggested that gravity is not a force but the consequence of bodies trying to follow straight paths in a 4D space-time but appear as a curved path in a 3D space like ours. Does it mean that the earth is not really orbiting around the sun but following a straight path in a 4D space-time? How abt. Prof. Hawkings suggestion in his proposal of a theory of quantum gravity that "curved space" must be taken Euclidean, does it mean to make the curved space re-appear as perfectlly flat? I am just wondering if it is possible to view such theory physically through a computer generated animation?

sirjon
2009-Jul-31, 08:38 AM
I view it this way: "Imagine the earth circling around the sun. Now imagine the sun and the earth gradually getting larger with the distance bet. them increases (space-in-between bodies getting wider). In doing that, the earth's path as a "curved orbit" may then appear to be straight path? Am I'm right?

slang
2009-Jul-31, 09:34 AM
These are normal questions, do you have a particular reason to post them in the ATM forum instead of Questions&Answers? (And as a small aside, your posts would be better readable if you would not use unusual abbreviations like abt. and bet.)

gzhpcu
2009-Jul-31, 05:37 PM
Thing is we still do not know whether or not gravity is a force or a geometric distortion of spacetime due to the presence of matter.

Considering the current prime candidate for unification, M-theory, the latter does not think of gravity as warping spacetime.

Cougar
2009-Jul-31, 05:58 PM
Does it mean that the earth is not really orbiting around the sun but following a straight path in a 4D space-time?

We're pretty sure the earth is really orbiting the sun. :) In GR, the word "straight" is a bit ambiguous. This is not Euclid's geometry.

DrRocket
2009-Jul-31, 05:59 PM
I am just curious. General relativity suggested that space is not really flat but actually curved or warped by the presence of matter and energy on it. It also suggested that gravity is not a force but the consequence of bodies trying to follow straight paths in a 4D space-time but appear as a curved path in a 3D space like ours. Does it mean that the earth is not really orbiting around the sun but following a straight path in a 4D space-time? How abt. Prof. Hawkings suggestion in his proposal of a theory of quantum gravity that "curved space" must be taken Euclidean, does it mean to make the curved space re-appear as perfectlly flat? I am just wondering if it is possible to view such theory physically through a computer generated animation?

"Curved" refers to the curvature tensor in terms of differential geometry. It may not mean quite what you think it means.

What is curved is space-time, not simply "space". In fact there is no global definition of what is meant by "space".

I don't know if Thomas Banchoff (http://www.math.brown.edu/~banchoff/) has ever attempted his simulations with Lorentzian manifolds or not, but he is known for his work at Brown University in producing computer-generated graphics of 3-dimensional slices of 4-manifolds.


Thing is we still do not know whether or not gravity is a force or a geometric distortion of spacetime due to the presence of matter.

Considering the current prime candidate for unification, M-theory, the latter does not think of gravity as warping spacetime.

Before M-theory replaces general relativity, someone is going to have to figure out what M-theory actually is. That seems to be the major open question in the area.

sirjon
2009-Aug-01, 07:33 AM
I am just wondering that the basic postulate of gen. relativity originally was to assume that the gravitational field, that is,bodies near the earth is equal to accelerating body such a man inside an elevator, (w/c is not really a new idea as I thought of it) swiftly accelerating at 9.8meters per sec squared was introduced by Einstein in 1915, when people thought the universe was static. In 1924, Hubble discovered that our universe is expanding but recent studies shows that the universe not only expanding, the rate of expansion seems to be in a fast pace. Maybe, Einstein assumed that space is curve to match it to his model of a static universe. If Hawking's proposal to make it appear ( the curved space) to be flat, I assume that to achieve a straight path, relative bodies like the earth orbiting around the sun should appear expanding in a three-dimensional pattern. Do you think it is valid?

sirjon
2009-Aug-03, 02:58 AM
Scientists are baffled by the possible existence of dark matter and dark energy. But they're seem to be clueless of what these entities really are and even proposing a similar cosmological constant as anti-gravitational force. But to think that gravity is not an attractive force, therefore the existence of an anti-gravitational force would have no bearing at all. Is it possible that everything in the universe are possibly expanding three-dimensionally but we're not noticing it at near scale but in long range, that is, in light-years distance away, the evidence would be noticeable?

WayneFrancis
2009-Aug-03, 03:23 AM
sirjon, What don't you understand about what has previously been explained to you about your "Expanding Earth" idea being falsified by observation?

sirjon
2009-Aug-04, 03:08 AM
Ok thanks any way. Maybe you misinterpret me.Both the earth and the sun and the and the space in between them are expanding three dimensionally.Maybe this thread should be deal as under the category of "against mainstream".

WayneFrancis
2009-Aug-04, 03:27 AM
No, I understand you Sirjon but it has been pointed out to you how this can't be the case. Even if you some how get each body to expand at its average surface escape velocity and you have space expanding too you still have the problem that "escape velocity" is not uniform across a planet thus your model would have to expand at different rates and we would notice things like mountains shrinking from this. You also have the problem of not noticing all the other planets either expanding or shrinking relative to us because of the different amounts of gravity.

Simply put your model is not observed and isn't even mathematically possible.

Yes this belongs in the ATM but as it has been fully refuted before and I don't see you coming up with anything to address the issues already explained to you.

a1call
2009-Aug-08, 05:44 AM
Proposing that "everything(size, speed of light, orbits, ...)" scales up (or down for that matter) is stating nothing at all. Everything will cancel out. It's a bit like saying the new dollar is equal to double of the old dollar. No one gets richer nor poorer. Unless you leave something out of the assumed uniform scaling your model will be no different from a static non-scaling model and will be as incapable of describing/explaining gravity or anything else.
If you decide to leave something out of the uniform scaling, then you will have to deal with conflicts from a non-scaling model which is in agreement with observation.