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Imagine if the Sun disappears right now. When the Earth will be affected by its absence? Does it affect immediately, or it takes almost 8 minutes? (The time that light travels from the Sun to the Earth.)

So if I ask this question in another way, the changes in Space-Time will affect immediately or it will travel by light speed?

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As we know by General Relativity, gravity propagates by the speed of light c = 299,792,458 m/s in a vacuuum (like space).

The average distance between the earth and sun is about 149.6 million kilometers, so it takes light about 8.3 minutes from the sun to earth.

This means, if the sun were to disappear right now, we would have to wait 8 minutes and 20 seconds until we would realize. Luckily, by all known laws of physics, this is not possible :)

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  • $\begingroup$ thank you for your answer I just found my answer and it's still magnificent that means with no mass we can have gravity effect. $\endgroup$ – Pouya Samie Aug 4 at 17:32
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I found my answer here :

it seems my question was already has been answered by Albert Einstein.it's called cosmic catastrophe. according to that page In Einstein's spacetime model, the disappearance of the sun would create gravitational waves in the spacetime. The gravitational waves travel at the speed of light, and an orbiting planet would not react to the sun's disappearance until after the gravitational wave has reached it. Only then, the planet would start to travel in a straight line.

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    $\begingroup$ Direct measurement of the speed of gravitational waves are still a little sparse: en.wikipedia.org/wiki/Speed_of_gravity Somewhere near lightspeed seems most reasonable. $\endgroup$ – Wayfaring Stranger Aug 4 at 20:56
  • $\begingroup$ thanks for your link, now i should have more question about gravity during inflation :) $\endgroup$ – Pouya Samie Aug 5 at 6:33
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In a very real and fundamental way "This can't happen" Not only practically (you can't make the sun disappear) But in a fundamental way, you can't make mass disappear.

Even if you suddenly converted all the mass of the sun into energy, that energy would still have a gravitational effect. And removing the mass of the sun, at speeds greater than the speed of light fundamentally breaks the very physical laws which you need to base any answer on.

So this is a frame challenge answer. It is theoretically impossible to make mass disappear.

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  • $\begingroup$ Black hole, traveling at 0.99c, having the same radius as the sun, slams smack dab into into it. Not at all likely, but not illegal. It'd probably turn all the inner planets into smears though. $\endgroup$ – Wayfaring Stranger Aug 5 at 20:56
  • $\begingroup$ Then there is mass moving at less than light speed, appoaching this sun and then leaviing at less than light speed fundamentally and importantly Mass can't disappear This is not a just a practical fact, but critical to general relativity. If the mass-energy of the sun could leave at more than light speed, then GR is completely wrong. $\endgroup$ – James K Aug 5 at 21:21
  • $\begingroup$ Right. I'm not disagreeing with that, just pointing out that the gravitational field of the sun could be made to nearly disappear quite rapidly. $\endgroup$ – Wayfaring Stranger Aug 5 at 23:58

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