Originally posted by twhiteheadWait, this is totally new to me. And this belongs in the Science Forum, yes, but I thought one of the great things about General Relativity is that what had previously been described as a force acting at a distance can now be described as curvature in space. What are the subtle differences? A quick reference to a website is acceptable--I don't expect an exhaustive treatise. I was just under the impression that there's actually no difference between "the force of gravity" and "a pathline through curved spacetime."
No it isn't. There are some subtle differences which have been tested and Einsteins predictions are what is observed.
Originally posted by convectHave a look at
Wait, this is totally new to me. And this belongs in the Science Forum, yes, but I thought one of the great things about General Relativity is that what had previously been described as a force acting at a distance can now be described as curvature in space. What are the subtle differences? A quick reference to a website is acceptable--I don't expect an e ...[text shortened]... ly no difference between "the force of gravity" and "a pathline through curved spacetime."
http://en.wikipedia.org/wiki/General_relativity
Go down to
Consequences of Einstein's theory
Note that light has no mass yet its path is affected by gravity. Time is also affected by gravity.
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Originally posted by KellyJaySo in mathematical terms your straight line is equivalent to my straight line in all dimensions. The only problem is that your straight line is not a very useful concept as it cannot exist in reality, and worse, it might be impossible to identify one as we cannot identify all the dimensions.
Straight, is a line that is in one direction without bends, curves, or any type of irregularities without any deviation of any type what so ever.
Kelly
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Originally posted by KellyJayAs I said, there are subtle differences, and the observations support the fact that space itself is curved by mass - or something even more bizarre is going on. Newtonian mechanics just doesn't cut it. GPS would not work if this was not true.
You are wrong, if it forces something to bend it is acting upon it. It is
no dfferent than a ship at sea that is setup to run a straight course,
but is throw off course,because either the water or the wind causes it to
go off by altering its course.
Kelly
Originally posted by KellyJayA yard stick is straight in 3 dimensions. In two dimensions it is also straight and when you wrap a tape measure round a globe it remains straight in two dimensions.
Do this, find a globe lay a yard stick across on top of it does the
yard stick remain straight? Wrap a tape measure around it, did the
tape measure bend?
Define straight again and tell me did the globe change anything?
Kelly
What you can't handle is the fact that the yardstick is not straight in the fourth dimension.
Keep in mind that definitions are only about communication. The concepts under discussion would still be true even if you choose not to use the word 'straight'. It would still remain true that a balloon can expand within its two dimensional surface without entering any new areas of surface. A three dimensional universe can similarly expand its space dimensions without entering new areas of space. It can also have finite spacial dimensions.
Originally posted by twhiteheadYes, it would be a constant everywhere, hence straight. What you are
So in mathematical terms your straight line is equivalent to my straight line in [b]all dimensions. The only problem is that your straight line is not a very useful concept as it cannot exist in reality, and worse, it might be impossible to identify one as we cannot identify all the dimensions.[/b]
telling me is that your straight lines are not, they curve, they bend,
they turn around to the point they act like circles, and this some how
is 'good' for you, and your perceptions of reality are some how okay
with this.
Kelly
Originally posted by twhiteheadLOL, I'm sure your observations do give you fits when your straight
As I said, there are subtle differences, and the observations support the fact that space itself is curved by mass - or something even more bizarre is going on. Newtonian mechanics just doesn't cut it. GPS would not work if this was not true.
lines curve back and behave like circles. I'd say some of your
foundational views about reality and how it is put together are more
than a bubble off center.
Kelly
Originally posted by twhiteheadRealty is where we are, if you want to debate the universe as if we were
A yard stick is straight in 3 dimensions. In two dimensions it is also straight and when you wrap a tape measure round a globe it remains straight in two dimensions.
What you can't handle is the fact that the yardstick is not straight in the fourth dimension.
Keep in mind that definitions are only about communication. The concepts under discussion would ...[text shortened]... e dimensions without entering new areas of space. It can also have finite spacial dimensions.
living in a bugged computer program where a straight line that leaves
on the left side of the monitor, then comes back on the right side so
the ends meet I’d say speak to someone else, I’m not interested in
such a discussion.
A tape measure wrapped around a globe is not straight, it may have
the appearance of being straight from a narrow perspective, but that
would be an illusion, if you looked right at that tape measure you'd
notice something odd! The markings for the tape’s measurements
would be different in size. That would be due to the fact that the tape
measure isn't a straight line, but in fact it is curving around the globe.
The point closes to you would be close to actually reflecting an inch,
but it would be smaller than a true inch. In addition the closer to the
edge of the globe where it wraps around it and goes out of sight the
ability to see the full inch would be much smaller, making it very
limiting.
Kelly
Originally posted by KellyJayYou are still hung up on definitions of words. 'Straight' is just a word, and we must define it in a way that is useful to us. If find my definition useful, and it happens to match the most common usage of the word. I don't see definitions as 'good' or 'bad'.
Yes, it would be a constant everywhere, hence straight. What you are
telling me is that your straight lines are not, they curve, they bend,
they turn around to the point they act like circles, and this some how
is 'good' for you, and your perceptions of reality are some how okay
with this.
Kelly
However I realize that what you really want to do is avoid the actual argument by getting hung up on definitions. You wish to try and belittle my argument with references to 'another straight line circle argument' which you then hope to dismiss as hogwash. That doesn't work. My argument remains valid whatever word you choose to use in places of 'straight'.
Originally posted by KellyJayAs I said, modern science is based on the observations. If I am a bubble off center then so is science in general - but I realize that you do believe that. I sure don't see you proposing any alternatives. Do you think that GPS devices are just working by accident or do you have another theory for why they work?
LOL, I'm sure your observations do give you fits when your straight
lines curve back and behave like circles. I'd say some of your
foundational views about reality and how it is put together are more
than a bubble off center.
Kelly
Originally posted by KellyJayBut straight lines by your definition do not exist in reality, so we are not having that discussion anyway. The discussion was straight lines by my definition.
Realty is where we are, if you want to debate the universe as if we were
living in a bugged computer program where a straight line that leaves
on the left side of the monitor, then comes back on the right side so
the ends meet I’d say speak to someone else, I’m not interested in
such a discussion.
We seem to be back to your age old tactic of using your definition of a word to try to disprove a claim made by me with my definition of the word. Thats bad logic.
Lets try your logic in reverse.
1. My definition of God: A little green man in my refrigerator.
2. I looked in my refrigerator and found no little green men.
3. Therefore your God does not exist.
Can you see the flaw?
Originally posted by twhiteheadAlso the universe as a whole is like a 4 dimensional sphere in that if you keep traveling in one direction you will eventually get back to where you started (a circle).------whitey--------------
Because space time is curved in higher dimensions. According to Einsteins General Theory of Relativity matter bends spacetime. When light bends around a star (a well known and observed fact), it still travels in a straight line, however since space is bent, it can meet up with another light beam that took the other way around the star. There is a sphere a ...[text shortened]... ou keep traveling in one direction you will eventually get back to where you started (a circle).
However , since points in the universe are defined 4 dimensionally and not 3 dimensionally how could one get back to where one started? It would have to take 0 time to travel in your "circle" otherwise you would arive at the same point 3 dimensionally but not 4 dimensionally because time would have moved on. Our position in the universe is not just defined 3 dimensionally so I don't see how this would work. I also think the idea of a 4d sphere is a bit misleading because a sphere is 3 dimensional.
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Originally posted by knightmeister…However , since points in the universe are defined 4 dimensionally and not 3 dimensionally how could one get back to where one started?...…
Also the universe as a whole is like a 4 dimensional sphere in that if you keep traveling in one direction you will eventually get back to where you started (a circle).------whitey--------------
However , since points in the universe are defined 4 dimensionally and not 3 dimensionally how could one get back to where one started? It would have to tak . I also think the idea of a 4d sphere is a bit misleading because a sphere is 3 dimensional.
By travelling in a straight line in 3-dimentions but with that line of travel being curved in 4-dimentions (and NOT curved in 3-dimentions)
…It would have to take 0 time to travel in your "circle" ….
No.
…otherwise you would arrive at the same point 3 dimensionally but not 4 dimensionally because time would have moved on. ..…
How do you logically go from “time would have moved on” to “not 4 dimensionally”?
-how does one logically follow from the other?
….I also think the idea of a 4d sphere is a bit misleading because a sphere is 3 dimensional. …
Not THIS sphere! The sphere we are referring to is the 4d sphere that is roughly the shape of our universe -and nobody is saying that THIS sphere is a 3-dimensional one! So it is not “misleading” to say THIS sphere is 4d because it really IS 4d!
I have to ask, just for clarification:
The surface of our earth is two-dimensional. Two coordinates is enogh to descrabe any point's location on this surface. You don't need a third dimension to describe any points of this spherical surface.
Same as the universe, you don't need a fourth spatial dimension to describe a spherical space. It only needs thre coordinates to describe the location of any point in universe. Three dimensions are enough.
As a great circle is one-dimensional of the two dimensional earth surface, so is a great circle one-dimensional of the three dimensional universe.
Some of you say that the universe has four spatial dimensions, why? What's the fourth dimension for?
I think this confuses JK and gives him fuel to his twisted ideas...
Originally posted by knightmeisterI was talking about 4 spacial dimensions, so if we include time that makes 5!
However , since points in the universe are defined 4 dimensionally and not 3 dimensionally how could one get back to where one started? It would have to take 0 time to travel in your "circle" otherwise you would arive at the same point 3 dimensionally but not 4 dimensionally because time would have moved on. Our position in the universe is not just def ...[text shortened]... . I also think the idea of a 4d sphere is a bit misleading because a sphere is 3 dimensional.
Also, I was not talking about actually making the journey as there are limitations to actual travel, but drawing a theoretical line through space without considering the progress of time as you draw.
In reality, the universe is expanding so fast that you could not actually now complete a round trip due to the limitation of the speed of light.
I am not sure if we have yet reached it, but there is a point in the universes expansion when light from one part of the universe will never reach all other parts of the universe due to the expansion rate between the two points exceeding light speed.
The cool question is then whether or not points that can never interact with us can actually be said to exist.