Questions regarding Albert Einstein's theory that posits, among other things, the equivalence of mass and energy.

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Observing a point 13.82b ly away, 1b years ago

I understand that we can observe far away galaxies to get an idea how the universe looked like in the past. Assuming the universe is 13.82b years old, would it be correct to say that if we looked at ...
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1answer
59 views

Gravity assist: why is the velocity doubled? [closed]

The Wikipedia article has this terrestrial analogy: Imagine standing on a train platform, and throwing a [tennis] ball at 30 km/h toward a train approaching at 50 km/h. The driver of the train sees ...
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Time and velocity [migrated]

Suppose two cars are traveling at a velocity of c/2 (c=velocity of light) in two straight lines parallel to each other but in opposite direction in vacuum.... Then what will a person sitting in one of ...
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1answer
71 views

What is the bulk Lorentz factor?

When we are talking about relativistic motions, say from a relativistic jet, what is meant by the term "bulk Lorentz factor", and the bulk speed, $\beta$?
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1answer
34 views

Exoplanets and relativity [duplicate]

Ok, so I have read about how exoplanets are found using all sorts of genius methods. I also understand the further an obect in a telescope is the further into the past I am looking. So given that ...
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2answers
169 views

In theory, is there anywhere in the universe where velocity=0?

Earth is traveling at a certain velocity. Earth orbits the Sun at velocity X. The sun is orbiting the center of our galaxy at velocity Y. The galaxy is orbiting (something?) at velocity Z. On and ...
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2answers
979 views

Age of the universe and time dilation

Given our knowledge and the standard cosmological model, we estimate that the age of the universe is about 13.7 billion years old. How much sense does it make to talk about the age of the ...
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2answers
255 views

time on earth compared to completely stationary in space

I recently started trying to understand the theory of relativity and I have the following question. Because earth is orbiting the sun at approx 67,000 mph (and its my understanding time slows down ...
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1answer
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How would Special relativity explain past-present-future if thinking about 13-billion-light-years distanced objects

Halo. I'm interested in how would Special relativity comment on this: Suppose there are 2 objects, A and B. They are 13 billion light years away from each other. When the light from the B object ...
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What happens if two galaxies collide very quickly?

What would happen if two galaxies collided very quickly (e.g. at near the speed of light)? Would they mostly just pass through eachother unscathed, or would there be very energetic collisions that ...
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1answer
111 views

Thought experiment about the outskirts of the universe [closed]

Suppose I aim at some object that is 13 billion light years away from Earth. Let's assume I have a twin that pilots a ship that travels in infinite speed, meaning that he can reach that object and ...
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1answer
217 views

If an object with mass were to somehow go the speed of light, would it destroy the whole universe?

Would an object with mass traveling the speed of light destroy the whole universe because it would have infinite energy / mass? According to ...
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1answer
2k views

Would time go by infinitely fast when crossing the event horizon of a black hole?

If you were to fall into a black hole, my understanding is that from your reference point, time would speed up (looking out to the rest of the universe), approaching infinity when approaching the ...
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2answers
119 views

Length contraction of a star

Something moving toward or away from us will be contracted in length according to special relativity. As the M31 galaxy is moving toward us at great speed it's "depth" should appear slightly ...
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1answer
103 views

Did time pass more slowly in the past?

13 billion years ago, the universe was about 600 million years old according to many scientists. At that time, all matter in the universe would have to be closer, or in other words denser. Did time ...
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3answers
372 views

Does gravity slow or speed light up?

The speed of light in a vacuum is presumably the fastest speed possible. if gravity bends the course of light, does this imply that gravity the retards light so it is moving at a slower speed? If ...