# All Questions

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### How exactly does time slow down near a black hole?

How exactly does time slow down near a black hole? I have heard this as a possible way of time traveling, and I do understand that it is due in some way to the massive gravity around a black hole, but ...
304 views

### Electron orbits

Is there an upper limit to the number of orbits an electron can have around say a proton? Aren't there states that are unstable (for $n\ne1$) with corresponding mean/half lives and therefore ...
441 views

### Artificial Gravity - Spinning Station Questions II

In an answer to Artificial Gravity - Spinning Station Questions Vintage wrote: A theoretical space station of radius 900 meters, doing a complete rotation every 60 seconds (in order to generate ...
655 views

### Example of a wavefunction that cannot be represented by a single Slater determinant

I know that in general, interacting fermions cannot necessarily be described by a single Slater determinant. Can anyone provide a simple example of a state that has no such representation?
2k views

### Free particle in magnetic field / Landau quantization

I have a question concerning a possible derivation of the Landau quantization. In our lecture notes (and some other places as well), the following ansatz is used:  \Psi(x,y,z) = \exp{\left(-j(\...
7k views

### How to find the Andromeda galaxy without using a go-to telescope?

In other words, what is the proper technique (star-hopping or other?) in order to find and properly point a telescope to this target? Would a star atlas or other tool/reference help? Can I use the R.A....
742 views

### Artificial Gravity - Spinning Station Questions

I've done a little research but I can't seem to find the answers to these questions in regards to a spinning space station simulating gravity. If we imagine the space station as a hollow doughnut and ...
10k views

### Ascent rate and size of balloon

I am part of a school project, Project Stratos to send a balloon to the edge of space (the closer side :P) and was wondering how you would work out the accent rate of a large balloon (roughly 1m^3 of ...
10k views

### How would you describe a black hole to a complete layman?

Non-astrophysicist visitors to Black Hole, will most likely barely make it past the introduction before getting lost in the technical details. Moreover, the Wikipedia article does not teach laypeople ...
6k views

5k views

### How do you calculate the intensity of light around the focal point from a focused collimated beam of light?

Problem/Purpose of me asking this question to you people who know more than me: So I'm doing a science project where I'm collimating a beam of light to a focus point in a light medium (water vapor or ...
3k views

### What happen when a gas is being heated far beyond its boiling point?

let's say we pour some water to the Sun. Or boil water on 2000 degrees Celsius on Earth.
489 views

### what cools bottle of water faster: ice or snow

Imagine you have a pile of snow and a pile of ice shards. You put a soda bottle which has a room temperature into both piles. Which bottle is going to cool down faster?