Scientists depiction of gravity as bowling ball on trampoline

Could some one explain this. It seems kindof like they are saying, look gravity makes gravity. Is there some type of relation in the acceleration of a  marble rolling around next to the bowling ball. Yeah i get it definitely looks cool and fun to think about.... but if there wasnt gravity then the bowling ball wouldnt do that in the first place, so what is the point of this image if their is not some correlation in the acceleration factor or something. Am i missing something, what is this all about. How is it helpful.

It’s alright saying that mass bends space so there is gravity, but that is a difficult concept and how does the former create the latter, the experiment shows in a way how it works, now you just have to extrapolate into four dimensions.

It helped me when I was a kid.




edit clarity i hope

As Jura pointed out, it'a visual aid for understanding the concept of relativity.

There is a beautiful analogy involving a bowling ball and a marble on a trampoline. Imagine placing the bowling ball on the surface of the trampoline. This acts to curve the trampoline in a region around the ball, analogous to the curvature of space-time around a massive object such as the sun.


It' not meant to be a demonstration of, "See? Gravity!"

It's literally just an analogy to visually help someone understand the concept. In other words, it's not meant to be proof of anything, if that's what you're thinking.

  Am i missing something, what is this all about. How is it helpful.

How would you depict the relationship between space-time and objects with mass? 

Even showing three-dimensional objects on a two-dimensional surface like a monitor or a piece of paper is problematic.  There is really no single good way to show the three-dimensional spherical earth on this screen, is there?

This...

... is not how an atom looks but it has educational value nonetheless.

It is a visual aid, and an approximation.

It takes 2D space (the trampoline surface) and shows a simplification of how it is distorted through a time axis.
Then an object on that surface will naturally travel in apparently curved paths, such as orbiting the primary.

Gravity is just used to make the analogy because it is easy to do, and responsive. But it could just be constructed rigidly in that shape (or the shape of any hypothetical gravity well).

It’s alright saying that mass bends space so there is gravity, but that is a difficult concept and how does the former create the latter, the experiment shows in a way how it works, now you just have to extrapolate into four dimensions.

It helped me when I was a kid.




edit clarity i hope

Why are they showing us this image and no extrapolation.

Quote from: faded mike on January 13, 2023, 08:21:18 AM

  Am i missing something, what is this all about. How is it helpful.

How would you depict the relationship between space-time and objects with mass? 

Even showing three-dimensional objects on a two-dimensional surface like a monitor or a piece of paper is problematic.  There is really no single good way to show the three-dimensional spherical earth on this screen, is there?

This...

... is not how an atom looks but it has educational value nonetheless.

It seems the opposite would also seem true that everything is connected by stretched springs that pull and accelerate most when closest. and there we have the wave property of a spiral that they say is really  the case... a duality.... You should see the image Sandokhan posted of the actual scanning electron image of a surface of molecules - it looked something like square pattern of alternating bumps and holes like an egg carton or sound insulation.

Quote from: Jura-Glenlivet II on January 13, 2023, 08:41:08 AM

It’s alright saying that mass bends space so there is gravity, but that is a difficult concept and how does the former create the latter, the experiment shows in a way how it works, now you just have to extrapolate into four dimensions.

It helped me when I was a kid.




edit clarity i hope

Why are they showing us this image and no extrapolation.

Who is "they"?

Why are they showing us this image and no extrapolation.

Because FEers like cherry picking things to pretend their are faults?
Because it is just made as a simple explanation to explain.
Because a more complex 4D explanation can be quite complicated and hard to understand.

It seems the opposite would also seem true that everything is connected by stretched springs that pull and accelerate most when closest.

No, it doesn't, as that would keep them connected. But they can exchange neighbours.

You should see the image Sandokhan posted of the actual scanning electron image of a surface of molecules - it looked something like square pattern of alternating bumps and holes like an egg carton or sound insulation.

I have seen plenty of them. SEM images are only able to resolve down to the atomic scale (if that, most don't go that far, and the good images are either TEM or STM).
That matches the known model of the atom.

Quote from: Jura-Glenlivet II on January 13, 2023, 08:41:08 AM

It’s alright saying that mass bends space so there is gravity, but that is a difficult concept and how does the former create the latter, the experiment shows in a way how it works, now you just have to extrapolate into four dimensions.

It helped me when I was a kid.




edit clarity i hope

Why are they showing us this image and no extrapolation.

It's representative, when the trampoline is flat,that is normal space time, if the bowling ball is on a flat surface with a marble near, the marble stays where it is, however adding the bowling ball to the trampoline warps the 2d surface like a planet warps space time, such that a marble near it now falls down the well created by the bowling ball, showing representatively the gravity well a 3d warping of spacetime creates, it's by no means perfect but it's a clever symbol of why big things draw smaller ones.     

The trampoline demonstration is not a good demonstration of the mechanics of General Relativity. It is far more complex. In RE General Relativity the surface of the earth is accelerating upwards through unseen dimensions in curved space-time to cause the Equivalence Principle effects while maintaining a round world. It is a metaphysical theory used to explain why the surface of earth appears to be accelerating upwards in RE.


See - Gravity: A Very Short Introduction by Cosmologist Timothy Clifton

“ Consider a skydiver jumping out of an airplane. The skydiver falls freely, up to the effects of air resistance. According to Einstein, the skydiver's path is the straightest line possible through the curved space-time around the Earth. From the skydiver's perspective this seems quite natural. Except for the air rushing past her, the skydiver feels no perturbing forces at all. In fact, if it weren't for the air resistance, she would experience weightlessness in the same way that an astronaut does in orbit. The only reason we think the skydiver is accelerating is because we are used to using the surface of the Earth as our frame of reference. If we free ourselves from this convention, then we have no reason to think the skydiver is accelerating at all.

Now consider yourself on the ground, looking up at the falling daredevil. Normally, your intuitive description of your own motion would be that you are stationary. But again this is only because of our slavish regard to the Earth as the arbiter of what is at rest and what is moving. Free yourself from this prison, and you realize that you are, in fact, accelerating. You feel a force on the soles of your feet that pushes you upwards, in the same way that you would if you were in a lift that accelerated upwards very quickly. In Einstein's picture there is no difference between your experience sanding on Earth and your experience in the lift. In both situations you are accelerating upwards. In the latter situation it is the lift that is responsible for your acceleration. In the former, it is the fact that the Earth is solid that pushes you upwards through space-time, knocking you off your free-fall trajectory. That the surface of the Earth can accelerate upwards at every point on its surface, and remain as a solid object, is because it exists in a curved space-time and not in a flat space.

With this change in perspective the true nature of gravity becomes apparent. The free falling skydiver is brought to Earth because the space-time through which she falls is curved. It is not an external force that tugs her downwards, but her own natural motion through a curved space. On the other hand, as a person standing on the ground, the pressure you feel on the soles of your feet is due to the rigidity of the Earth pushing you upwards. Again, there is no external force pulling you to Earth. It is only the electrostatic forces in the rocks below your feet that keep the ground rigid, and that prevents you from taking what would be your natural motion (which would also be free fall).

So, if we free ourselves from defining our motion with respect to the surface of the Earth we realize that the skydiver is not accelerating, while the person who stands on the surface of the Earth is accelerating. Just the opposite of what we usually think. Going back to Galileo's experiment on the leaning tower of Pisa, we can now see why he observed all of his cannonballs to fall at the same rate. It wasn't really the cannonballs that were accelerating away from Galileo at all, it was Galileo that was accelerating away from the cannonballs! ”

Also see: Why Is Spacetime Curved? in the book Time Travel in Einstein’s Universe by John Richard Gott III, professor of astrophysical sciences at Princeton University -

“ A famous (perhaps apocryphal) story about Einstein describes one occasion when he fell into conversation with a man at the Institute for Advanced Study at Princeton. During their chat, the man suddenly pulled a little book from his coat pocket and jotted something down. Einstein asked, “What is that?" “Oh,” the man answered, “it's a notebook I keep, so that any time I have a good idea I can write it down before I forget it.” “I never needed one of those," Einstein replied. “I only had three good ideas.”

One of them occurred to him in 1907—what he would later call the “happiest” idea of his life. Einstein noted that an observer on Earth and an observer on an accelerating spaceship in interstellar space would have the same sensations. Follow this chain of thought to see why. Galileo had shown that an observer dropping two balls of different mass on Earth sees them hit the floor at the same time. If an observer in an accelerating rocket in interstellar space performed the same experiment, dropping two balls of different mass, they would float motionless in space—but, since the rocket was firing, the floor of the spaceship would simply come up and hit both of them at once. Both observers thus should see the same thing. In one case, it is the result of gravity; in the other case, it is caused by an accelerating floor with no gravity involved. But then Einstein proposed something very bold—if the two situations looked the same, they must be the same. Gravity was nothing more than an accelerated frame-of-reference. Likewise, Einstein noted that if you get in an elevator on Earth and cut the cable, you and everything in the elevator will fall toward Earth at the same rate. (Galileo again—objects of different mass all fall at the same rate.) So, how do things look to you in the falling elevator? Any object you drop will float weightless in the elevator—because you, the object, and the elevator are all falling at the same rate together. This is exactly what you would see if you were in a spaceship floating in interstellar space. All the objects in the spaceship, including you, would be weightless. If you want to experience weightlessness just like an astronaut, all you have to do is get in an elevator and cut the cable. (This works, of course, only until the elevator hits bottom.)

Einstein's assertion that gravity and acceleration are, the same—which he called the equivalence principle—was influenced, no doubt, by his previous success in equating the situation of a stationary magnet and a moving charge with that of a stationary charge and a moving magnet. But if gravity and accelerated motion were the same, then gravity was nothing but accelerated motion. Earth's surface was simply accelerating upward. This explained why a heavy ball and a light ball, when dropped, hit the floor at the same time. When the balls are released, they just float there—weightless. The floor (Earth) simply comes up and hits them. What a remarkably fresh way of looking at things!

Still one must ask how Earth’s surface could be accelerating upward (away from Earth's center) if Earth itself is not getting bigger and bigger with time like a balloon. The only way the assertion could make sense is by considering spacetime to be curved.

Einstein proposed that mass and energy cause spacetime to curve. It took him 8 years of hard work to derive the equations governing this. He had to learn the abstruse geometry of curved higher dimensional spaces. He had to learn about the Riemannian curvature tensor—a mathematical monster with 256 components telling how spacetime could be curved. This was very difficult mathematics, and Einstein ran upon many false leads. But he didn't give up because he had great faith in the idea. ”

Also see this quote on p.65 in Relativity Visualized by Lewis Carroll Epstein -

“ Einstein’s view of gravity is that things don’t fall; the floor comes up! ”

Note that each body has a specific inertial resistance. It should take more force to move a bowling ball through space than a marble. Hence why it is curious that they 'fall' at the same rate in a vacuum. In reality all bodies, and even individual types of atoms, have different masses and it is quite curious that they are all pulled at the same rate through space and towards the earth without differences.

Also see this quote on p.65 in Relativity Visualized by Lewis Carroll Epstein -

“ Einstein’s view of gravity is that things don’t fall; the floor comes up! ”

You seemed to have left out some context (My bold):

"If you wanted to interpret the unrolled spacetime diagram literally, you could say the house has an upward acceleration of one g. In a nutshell, Einstein’s view of gravity is that things don’t fall ; the floor comes up! That easily explains why heavy objects don’t fall faster than light objects. But don’t take it too literally, because if the floor is coming up in both New Orleans and Calcutta, the earth’s diameter could not remain 8000 miles."

Quote from: Tom Bishop on January 16, 2023, 01:18:02 PM

Also see this quote on p.65 in Relativity Visualized by Lewis Carroll Epstein -

“ Einstein’s view of gravity is that things don’t fall; the floor comes up! ”

You seemed to have left out some context (My bold):

"If you wanted to interpret the unrolled spacetime diagram literally, you could say the house has an upward acceleration of one g. In a nutshell, Einstein’s view of gravity is that things don’t fall ; the floor comes up! That easily explains why heavy objects don’t fall faster than light objects. But don’t take it too literally, because if the floor is coming up in both New Orleans and Calcutta, the earth’s diameter could not remain 8000 miles."

Yes. See the previous citations. They describe the same thing. The reason the earth's diameter doesn't increase under this view is because this is happening in curved space-time.

The trampoline demonstration is not a good demonstration of the mechanics of General Relativity. It is far more complex. In RE General Relativity the surface of the earth is accelerating upwards through unseen dimensions in curved space-time to cause the Equivalence Principle effects while maintaining a round world. It is a metaphysical theory used to explain why the surface of earth appears to be accelerating upwards in RE.

Just what part is unseen?

Under GR, an inertial reference frame is a geodesic through spacetime. This just uses the dimension of space and time.
That would cause Earth to collapse into a ball. It is accelerating outwards, away from the centre, due to the internal pressure.

This does not require any unseen dimension.

Quote from: Tom Bishop on January 16, 2023, 01:18:02 PM

The trampoline demonstration is not a good demonstration of the mechanics of General Relativity. It is far more complex. In RE General Relativity the surface of the earth is accelerating upwards through unseen dimensions in curved space-time to cause the Equivalence Principle effects while maintaining a round world. It is a metaphysical theory used to explain why the surface of earth appears to be accelerating upwards in RE.

Just what part is unseen?

Under GR, an inertial reference frame is a geodesic through spacetime. This just uses the dimension of space and time.
That would cause Earth to collapse into a ball. It is accelerating outwards, away from the centre, due to the internal pressure.

This does not require any unseen dimension.

Incorrect. Einstein theorizes an unseen realm where things happen called space-time.

https://www.cnet.com/science/features/the-general-relativity-rabbit-hole-unraveling-space-time-and-the-fourth-dimension/

Basically, Einstein realized that space is much more than the "space" we live in and that time transcends the clocks we've invented. Rather, he theorized, the two are physically entangled.

Space is like a canvas on which our past, present and future are woven -- and it can fold, twist and ripple like silk. There's no beginning or end to this fabric of space and time, or as he called it, spacetime.

We can't exactly see the spacetime continuum because it's part of a realm imperceptible to human eyes: the fourth dimension. But we can deduce its existence, as we can feel its effects.

See: "We can't exactly see the spacetime continuum because it's part of a realm imperceptible to human eyes: the fourth dimension."

See also:

https://www.jstor.org/stable/20012625

"Parties to those discussions generally share at least one of Einstein's basic principles: A spacetime theory postulates the existence of an unobservable object (spacetime) in order to explain observable phenomena (relative motions)"

Under GR, an inertial reference frame is a geodesic through spacetime. This just uses the dimension of space and time.
That would cause Earth to collapse into a ball. It is accelerating outwards, away from the centre, due to the internal pressure.

This does not require any unseen dimension.

Okay, sorry, I need to be a pain for a second. An inertial reference frame is not a geodesic. A geodesic is just the generalised notion of a straight line for anything other than Euclidean (ie: old-school intuitive, sans-relativity) space - the geodesic would essentially be the way to find the distance between two points, while an inertial reference frame is just your perspective while keeping at a constant velocity.
You can observe a geodesic from within an inertial reference frame, which might be what you meant in response to Tom.

But more on-topic, calling spacetime unseen is completely accurate, and thoroughly unhelpful. We cannot physically see spacetime, Tom's right about that, but we can detect it and measure it, and relativity has made predictions that have been experimentally verified. Spacetime is as observed as this post is observed by you right now - we observe its effect on other things (in the case of this post, light).

See also:

https://www.jstor.org/stable/20012625

"Parties to those discussions generally share at least one of Einstein's basic principles: A spacetime theory postulates the existence of an unobservable object (spacetime) in order to explain observable phenomena (relative motions)"

Okay, so quoting this guy:
https://publish.uwo.ca/~rdisalle/
"History and philosophy of science, especially the history and philosophy of physics from Newton to the present; philosophical problems of space and time; history of the philosophy of science, from the 17th century to the present; connections between philosophy of science and analytic philosophy."

The philosophy underpinning relativity isn't what most people in this thread are discussing. That might be a disconnect.

Incorrect. Einstein theorizes an unseen realm where things happen called space-time.

Incorrect.
This is a combination of space, the 3 commonly known spatial dimensions, and time, something we all experience.

It does not require any unseen realm.

I'll even be nice and provide a quote from your article:
"In 3D, we have an X axis for length, Y for width and Z for depth. In 4D, there's a fourth axis: Time."
The fourth dimension of space-time is time. It is not some magically extra dimension that Earth's surface is accelerating through.
It is accelerating outwards.

Okay, sorry, I need to be a pain for a second. An inertial reference frame is not a geodesic. A geodesic is just the generalised notion of a straight line for anything other than Euclidean (ie: old-school intuitive, sans-relativity) space - the geodesic would essentially be the way to find the distance between two points, while an inertial reference frame is just your perspective while keeping at a constant velocity.

My bad, I meant an inertial reference frame follows a geodesic through space time.
Which is still poorly worded.
Borrowing some of your wording perhaps this is better:
An inertial reference frame is your perspective while following a geodesic through spacetime.

But more on-topic, calling spacetime unseen is completely accurate, and thoroughly unhelpful.

I disagree, in the context of the discussion I see it as trying to make a comparison between the dimensions of spacetime and the dimensions of regular space.
As if Earth's surface was accelerating upwards through some magical extra dimension.

The dimensions of spacetime are just as seen as the dimensions of space, and the dimension of time.
Quite different to the allegedly tiny and unseen dimensions of string theory which are rolled up so small they can't be seen.

So calling spacetime unseen and calling space and time unseen are equally accurate.

You can try playing semantic games with highly specific definitions of seen to say you can't see any dimensions, similar to not being able to see any hole, but that would make the statement entirely useless; as it would be no different to saying something along the lines of "an unseen [thing which is impossible to see, regardless of what other traits are applied to it]".
Or you can not play those semantic games and allow a more general definition of seen, which allows you to see dimensions and accept that spacetime is seen.

An inertial reference frame is your perspective while following a geodesic through spacetime.

Ooh, neat description.
(I will admit, it makes the pedant in me scream, but that's more from being used to dealing with strictly space-dimensional geodesics. For relativity, I think that'd include time and so constant speed with no change in direction, so certainly would count as an inertial reference frame)

You can try playing semantic games with highly specific definitions of seen to say you can't see any dimensions, similar to not being able to see any hole, but that would make the statement entirely useless; as it would be no different to saying something along the lines of "an unseen [thing which is impossible to see, regardless of what other traits are applied to it]".
Or you can not play those semantic games and allow a more general definition of seen, which allows you to see dimensions and accept that spacetime is seen.

That was kinda what I was getting at - it's unhelpful because it is just playing with words, but it's not strictly-speaking untrue. He's focusing more on the metaphysics and philosophy than the practical physics you and I are, which is inevitably going to rely on using words differently and arriving at different results. It feels like an unhelpful approach, particularly in answer to this analogy which was never meant to explain underlying physics, but it isn't an inherently invalid approach.