So I saw this space time/gravity visualized shit and thought it was pretty neat. It's basically the universe as a 2D plane and when matter is present, it pushes down on it and makes other matter revolve around it (to describe gravity). I then realized that the theory of this was using gravity to describe gravity itself.
So, is this okay or not for it? Does that deem the theory false? Correct me if I'm wrong.
its taking the concept of mass in the 4-dimension effecting the 3rd dimension, but taking it down a knotch so humans can understand
so mass in the third dimension warps the second dimension, just how mass in the fourth dimension warps our percieved third dimension
It's just a way of representing the idea; In two-dimensional space, the equations of motion for balls rolling along curved space are the same as what's actually going on, so you get a feel for the dynamics of it and how curved space can cause motion. It's not a "theory" at all, just a way of presenting a system you can easily visualize and understand.
Gravity has not been proved to exist. It is a theory and a law but its actual existence is still to be determined. Look at the jpg. If gravity is a function of matter then our universe should be chaotic and lack cohesiveness, it is not - it is (roughly) spherical. Do you really believe that at th centre of our galaxy is a black hole(s) that 'keep' our solar system in place through gravitational attraction? Dark Energy permeates the bulk of or universe, it exxpresses a 'repulse' force on matter in proportion to the amount of matter. This repulsion is what keeps our universe in a cohesive state, it acts to maintain all bodies in a static position (unless acted upon by a outside force).
I've always wondered about this. Gravity is something that we can measure, but not adequately explain. We've managed thus far because knowing what something does is far more important mechanically than knowing why.
My personal theory is that total gravity is in fact the combined effect of two separate functions, and that one simply masks the other.
But this is true for all measurements (that I can think of).
Take, for example, electromagnetic fields. We can't measure an electromagnetic field. What we actually do is measure e.g. electromagnetic repulsion at several spatial points, then extrapolate from the result that such a thing as an EM field exists (please no semantic arguments about the word exists, you should understand what I mean unless you're 11).
We are both wrong. A hypothesis implies testability. I am not saying that it is a testable statement, indeed if it were, the effect would not be masked and it would have been proven long ago.
I believe I waxed axiomatic.
I was initially confused by that too. What that rubber-sheet diagram is trying to show is something else though: gravity works by curving spacetime. If you were to take a toy car (whose wheels force it to follow a geodesic) and run it along that sheet, it would curve towards the ball, not because of gravity, but because of the non-zero curvature of the surface. It would curve towards the ball just as much if the ball were pushing the sheet upwards. It doesn't rely on a "meta-gravity" in the embedding space or anything like that.
>It would curve towards the ball just as much if the ball were pushing the sheet upwards.
I know you're trying to make it sound simply because OP is a layman, but spreading outright lies will not help anyone understand. Spacetime can be pushed "upward" or have a negative curvature and this would have the opposite effect that gravity has: pushing things apart. In fact, white holes are a special solution to Einstein's equations, similar to blackholes but they consist of negatively curved spacetime.
Nope. Take a look at the pseudosphere pic. If the ball produces negative curvature in the sheet, it doesn't matter whether the sheet is being pushed "upwards" or "downwards" in the diagram. The car will still deviate towards the ball. (Negative curvature seems backwards, but think about tidal forces: in the regions of space near a gravitating body, a passing pair of test particles will have worldlines that *diverge*, not converge. Curvature is negative there.)
Pick one and only one, buddy.
>We now know (as of 2013) that the universe is flat with only a 0.4% margin of error.
you see OP, this is just an analogy so that pop-sci fags like you will feel special enough for having heard it that you'll go out and buy kaku's latest book and also vote in legislators who will give academics more money
it's all a big ponzi scheme
We 'believe' as of 2013 etc
You do know that there are 2 'blind spots' in our surveillance due to the poles (and despite our earths 8 degree spin)? James Webb should correct this - however we can see 13.8 billion light years in every direction. Or can we?
Yea no meta gravity is required to understand the thought experiment of the ball on a sheet.
The sheet is space time, things follow space time because they have to, when its curved they move towards the thing curving it.
Its just illustrating the idea using warped flat plane because that's easier to imagine.
Everyone in this thread is wrong.
It is not just a pop sci phrase, it is the fucking formula for General Relativity, and YES it is a circular definition!
All narratives reduce to paradox. It is in the nature of the way we corroborate the world.
"Space tells mass how to move and mass tells space how to curve" is a "chicken and the egg" paradox. It comes from "inductive deconstruction".
Here are the rules. They come directly from the way the brain works:
1) All construction of narratives from set axioms lead to narratives that are incomplete.
2) All deconstruction of narratives leads to axioms that are paradoxically related.
The world is; the narrative is not.
But you cannot leave the narrative, so to use a meta- narrative to reflect the world and lead to some kind of understanding here it is:
The brain is a sense organ that sense itself, then tells itself what to sense, then sense itself...
See? Starts with a paradox, and BOOTSTRAPS the narrative.
Add in a comparative, and not binary elemental structure, and you get the morass that is the mind.
>"Space tells mass how to move and mass tells space how to curve"
That's not a paradox, or every single differential equation would be a paradox.
You're not half as smart as you think you sound, anon.
>It is kinda paradoxical.
No it's not. A paradox is statement that can be neither true nor false. It's also not 'weird' in the sense ascribed to maybe the 'twin paradox' in special relativity. One quantity influences the second, and the second the first. This is nothing new: In newtonian gravity, the mass influences the force on the particle, and the force between to objectst tells them how to move. This is physics 101.
>he's not wrong
Yes he is, see above.
No it's not.
One of the simplest models of friction depends on the speed of the object, so the faster you go, the more acceleration you experience which makes you go slower. These indertwined relations happen all the time.
It's just how differential equations work, though technically I don't think Einstein's equations are in the same class of differential equations since you solve for tensors.
Flat is infinite.
If the universe is flat or open, it will be infinite (spatially). If it is closed, then it will be spatially finite.
But what he said about curvature opposite to that of a normal gravitating body is true. I won't say positive or negative curvature, since that depends on your sign convention i.e de Sitter space is negatively curved in one sign convention and positively in another (and AdS space is the opposite, as the name suggests), but that is just convention and has no mathematical or physical meaning. These solutions generally involve negative energy, or a cosmological constant.
Dark energy is a part of general relativity. If it exists, so must gravity, because if not there is no framework in which the dark energy can act. Also, spacetime is "chaotic" because of gravity; it's just that this distortion is very small on cosmological scales.
Finally, galaxies do not need to have a large black hole at the centre to keep them together. The gravity of the stars pulls everything together - a black hole acts no differently to any other mass, at least from a distance.
Dark energy is a part of general relativity. If it exists, so must gravity.... Bold statements considering
a) we do not know gravity exists - we infer
b) we do not know de exists - we infer
The sheer size of any field that is projected to incorporate DE at between 60%-80% of the entire universe with matter (incorporating this 'stuff' called gravity) at 3% - 6% indicates - to me anyway - that it does NOT need gravity as a framework in which to act.
shit, man, is there one single thing you say that is right?!
flat can very well be finite. the surface of torus is flat but the torus is finte. i think you have no idea how to define curvature. here:
Also, positive and negative curvature have nothing to do with sign conventions. a sphere has positive curvature and a psudosphere ha negative curvature. for 2d surfaces it has to do with the concordance or discordance of ccurvature along two perpendicular lines through point. positive=concordance, negative=discordance. if you change the sign you actively change the shape of the space.
I'm not talking about manifolds in general.
When talking about the FLW metric, flat, open and closed have very specific meanings.
If you actually go ahead and calculate the curvature of (anti) de sitter space, I promise that the result will dpends on the sign convention (unless you absorb the sign into the cosmological constant). You know how to do that, right?
tl;dr fuck off
My friend don't even try to convince them. None of them have probably ever opened up a GR book. But since we are on the topic, is there a cleaner way of calculating curvature that doesn't involve ridiculous bookkeeping of partials (and more importantly, second partial derivatives)? How does one find the curvature if the metric isn't diagonal?
Totally agree. I dont believe in it. However the equations we have work. The Holometer at fermi lab should tell us..
What do you believe in? How do you explain massive bodies attracted to each other coupled with phenomena such as orbits and Earth's tidal forces? How do you interpret general relativity? I'm curious