# Tag Info

### What is a manifold?

What is a manifold? A manifold is a concept from mathematics that has nothing to do with physics a priori. The idea is the following: You have probably studied Euclidean geometry in school, so you ...
• 15.6k
Accepted

### Would touching a black hole of a small mass (the mass of an apple) cause you to spiral in and get dead?

This is just a quick calculation that shows what would happen to a black hole with a mass equal to the mass of an apple: It is shown that not only the builder of this black hole but also the whole ...
• 4,580
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### Why does the speed of an object affect its path if gravity is warped spacetime?

You're using the wording "curved spacetime", but you're still only thinking "curved space" with an independent, linear time. In your curvature model, you're assuming that moving ...
• 2,924
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### What if we shine a laser to east and another to west, will they arrive at the same time?

It depends on your frame of reference. If you are positioned by the laser on the Earth's surface you would observe the two laser beams to have the same speed and your would observe the two targets ...
• 8,803
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### Why is Andromeda only partially blue-shifted?

I am going to attempt an explanation based on this image that you posted a link to in the comments. What you are looking at here is a broad-band visible wavelength colour image of the Andromeda ...
• 133k
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### Why don't merging black holes disprove the no-hair theorem?

No. The no-hair conjecture applies to stable solutions of the Einstein-Maxwell equations. In the case of merging black holes, it applies to the end state of the merger into a single quiescent black ...
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### Why doesn't Einstein's general theory of relativity seem to work on Earth?

The short answer: general relativistic effects are mostly not noticeable on such a small scale (except in a few cases). For example, one common way to characterize the strength of a gravitational ...
• 630
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### Do planets orbiting stars emit gravitational waves?

Yes, but undetectably. The Earth-Sun system radiates a continuous power average of about 200 watts as gravitational radiation. As Wikipedia explains, “At this rate, it would take the Earth ...
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### Would touching a black hole of a small mass (the mass of an apple) cause you to spiral in and get dead?

No. A black hole created from something like an apple will still have the gravitational pull of an apple, so it's not going to suck you into it. If you swiped it it would pass through your hand, ...
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### If gravity is a pseudoforce in general relativity, then why is a graviton necessary?

While it's common to describe gravity as a fictitious force we should be cautious about the use of the adjective fictitious as this is a technical term meaning the gravitational force is not ...
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