Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Dhruv on 23/02/2021 15:36:06
-
So I am learning more about gravity,
And according to Albert Einstein gravity takes place when a particular mass bends the space and time causing a curve between the masses which lead the both of them to get attracted to each other and go to the higher mass.
So I was wondering telling that masses bend the space and time seems really cool but what actually is Space where everything exists and what is time which we are passing and don't know?
It's all making me fall in overthinking so I want some you to please explain me it in every single detail possible for both of our sales.
-
I think you should not try to think of the space between two masses as being curved in any way.
It is really just the mathematical model (the graphs) that look bent.
No one knows why this should be the case but is observed to be the case and so the mathematical model (relativity) which shows this effect (and makes incredibly accurate predictions)
As well as I have learned,space and time are treated as two sides of the same coin and it is the way they combine that changes when in the presence of mass or energetic processes.
Stand to be corrected as I have no formal learning apart from what I have picked up on these and other science forums.
-
So I am learning more about gravity,
And according to Albert Einstein gravity takes place when a particular mass bends the space and time causing a curve between the masses which lead the both of them to get attracted to each other and go to the higher mass.
Sounds like you have the rubber sheet analogy in mind, which is a very poor analogy. The concept of bent space is not wrong. If you take a cold steel ball the size of a planet and drill a hole through it and pass a tape measure through the hole and around the circumference, the circumference will be less than the diameter time π. That's not possible in flat Euclidean space.
No, time does not cause the curve. The more correct wording is that the curvature of spacetime is a function of stress energy which is described by the stress energy tensor. Tensor calculus is beyond most physics students, and so it's most often best to just fall back to Newtonian mechanics in which objects accelerate due to a force of gravity and not stress energy.
So I was wondering telling that masses bend the space and time seems really cool but what actually is Space where everything exists and what is time which we are passing and don't know?
This seems mostly a philosophical question. Space is a measure of the spatial separation between simultaneous events (and since simultaneity is frame dependent, the spatial separation between relatively stationary objects is frame dependent). Similarly, time is the temporal separation between two events at the same location in space, and the same frame-dependent relations apply.
The definition I gave is somewhat circular, but perhaps somebody else can answer better.
It is really just the mathematical model (the graphs) that look bent.
Then the tape-measure thing above would not be true. It's not just pretty pictures. It's no more remarkable than showing that the surface of Earth is bent by showing that the angles of a triangle drawn on it will add up to more than 180°. Similarly, a triangle drawn on a seemingly flat sheet near a gravity well might have its angles add up to less than 180°.
-
Then the tape-measure thing above would not be true. It's not just pretty pictures. It's no more remarkable than showing that the surface of Earth is bent by showing that the angles of a triangle drawn on it will add up to more than 180°. Similarly, a triangle drawn on a seemingly flat sheet near a gravity well might have its angles add up to less than 180°.
Yes,I get your point.If the contents of the space are distorted then you can say that the space itself is also distorted .
I sometimes ask myself what is the difference between space and the objects it contains.
Some kind of a symbiotic relationship,rather than just to say that the spatial and temporal distances are simply mathematical /physical measurements?
And physical objects seem slippery customers when approached at the quantum level.
-
And physical objects seem slippery customers when approached at the quantum level.
@Halc wasn’t talking about the quantum level, this is large scale stuff ;)
-
And physical objects seem slippery customers when approached at the quantum level.
@Halc wasn’t talking about the quantum level, this is large scale stuff ;)
Yes ,but I was wondering if there might be a symbiotic relationship** between objects and the space they exist in.
Might it not be necessary to address that question (if it is a good question) at all levels ?
(I appreciate that @Halc 's example was very concrete and entirely "large scale")
**In the sense that one might talk of an object/space duality(it is just a vague idea I have had recently)
Edit: I think this earlier thread elsewhere (2016) that I started relates to Halc's example. I found it then in some Feynman lecture notes on the internet.
https://www.scienceforums.net/topic/100967-physical-demonstration-of-the-curvature-of-spacetime/
Disappointingly ,though towards the beginning of the thread I was told those measurements were more theoretical than concrete .(it was a thought experiment)
No doubt there are other examples that lend themselves to more practical ways of verification?
-
Yes,I get your point.If the contents of the space are distorted then you can say that the space itself is also distorted .
I sometimes ask myself what is the difference between space and the objects it contains.
You can think of it the way you want, but I'll leave one example.
Suppose you have a large, strong flat brittle disk that can take an amazing amount of force, but cannot bend (cannot be distorted). The disk has the same radius as our steel planet.
So the disk is sitting there in empty space, and we saw the planet in half and move the two halves carefully to near the disk on either side, but preventing any touching. This will distort the spacetime in which the disk resides. The disk will shatter due to it being a Euclidean object trying to fit in non-Euclidean spacetime. If the the disk (the contents) distorted due to the stress-energy, then it wouldn't break, but it does because it's like trying to bend a cracker around a mug.
-
The disk will shatter
Is there an obvious pattern in the way it would shatter?
Would it shatter in a similar way to the windscreen of a car (lots of small pieces?)
Would the size of those pieces get larger as we got further from the centre?
Oh and would you get the same /similar effect if you were using the Newtonian model?
-
The disk will shatter
Is there an obvious pattern in the way it would shatter?
It would shatter as would any object whose circumference is too small, so sort of similar to a small bit of egg shell (a fragment of a sphere) squashed flat between two flat surfaces.
Oh and would you get the same /similar effect if you were using the Newtonian model
No. Newton's model did not have any bending of spacetime. There would just be force due to the object's own weight on itself.