# 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 ...
• 15.4k
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 ...
• 4,530

### If gravity isn't a force, then why do we learn in school that it is?

Because Newtonian gravity, where it indeed is considered a force, is a good enough approximation to the situations you consider in middle school (and beyond). General relativistic effects are very ...
• 120k
Accepted

Accepted

### 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 ...
• 8,640
Accepted

### 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 ...
• 126k

### 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 ...
• 2,746
Accepted

### 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 ...
• 51k