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Oke, so my mind is blown by Einsteins view on gravity, at least as far as I understand the basics and principles he based his views on.

One of the first things that struck me was that most of his equations were based on the fact the photons had no mass, something which is virtually impossible to verify experimentally and something I can not convince myself of.

Now he states that mass bends spacetime: in other words, objects can only move in straight paths, but because the "surface" of a path can be bent, the trajectory relative to the mass is bent. So as a reaction, I did the following thought experiment that would separate Newton from Einstein:

Image in space (completely empty) and two objects with mass M and m (whatever the values) placed from a distance R apart completely at rest. According to my interpretation of Einstein, nothing will happen because even if spacetime is bent they have no motion themselves. Our earth orbits the sun because it initially had a motion and is now travelling in an infinite straight line, which becomes an ellipse due to curvature. Newtons would of course state that in my thought experiment, the two masses would collide.

After I realized this, I started to question Einstein's view. Is my basic interpretation correct about Einstein, and how would you (expert/physics professor/lover) respond to this thought? I personally find it pretty confronting...

BTW I'm just a high school student, potentially going to Cambridge to study physical sciences...

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marked as duplicate by Kyle Kanos, user10851, BMS, Martin, ja72 Dec 18 '14 at 21:15

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  • $\begingroup$ possible duplicate of Why would spacetime curvature cause gravity? $\endgroup$ – Kyle Kanos Dec 18 '14 at 18:38
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    $\begingroup$ While original thinking is a valuable thing and I think it's great that you analyze critically what you hear, do you really think you can overthrow 100 years of established knowledge with a simple thought experiment? $\endgroup$ – Javier Dec 18 '14 at 19:01
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    $\begingroup$ During the development of relativity, you didn't have "quanta" of light. What you did have are Maxwell's equations, for which constant magnetic fields, constant electric fields, and EM waves are all consequences of the same framework. So it doesn't matter if you can't imagine how to test photons being massless. What matters is verifying the correctness of Maxwell's equations. THEN you come up with a frame transformation that leaves Maxwell's equations satisfied and voila, special relativity. $\endgroup$ – user12029 Dec 18 '14 at 19:48
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    $\begingroup$ I think we can safely conclude that whatever your interpretation of Einstein is, it's utterly wrong. Was there an actual question here? $\endgroup$ – CuriousOne Dec 19 '14 at 4:52
  • $\begingroup$ Javier Badia, I do not want to overthrow this, this thought just popped up and it surprised me. I knew for sure something was wrong with my understanding, Einstein would have solved this easily... $\endgroup$ – user209347 Dec 19 '14 at 16:19
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Your claim that nothing will happen because they initially have no velocity is where things start to go wrong. In fact everything in relativity has the same speed (the speed of light). A particle that looks to be "at rest" in some reference frame simply has all of its velocity pointing in the "time direction".

This is an intuitive reason why you would see time passing more slowly on a spaceship moving with high (spacial) velocity relative to you. More of their speed is in a "space direction" so less has to be in the "time direction" in order to make the overall speed c.

When space is curved by some mass in general it won't be the case that a worldline with all of its speed in the time direction is a valid "straight line" called a geodesic. Paths which are allowed have to obey the geodesic equation. In particular the spacetime around a spherically symmetric mass is what is called the Schwarzschild metric and a stationary (in space) worldline definitely isn't a solution to the geodesic equation with that metric.

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  • $\begingroup$ Oke, this is too complex for me. At least I see the my understanding of "at rest" is not the same as Einstein intended. $\endgroup$ – user209347 Dec 19 '14 at 16:22

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