11
votes
5answers
2k views

What happens to light and mass in the center of a black hole?

I know that black holes are "black" because nothing can escape it due to the massive gravity, but I am wondering if there are any theories as to what happens to the light or mass that enters a black ...
4
votes
2answers
594 views

How is the mechanism of greenhouse gases interacting with IR radiation?

How does atmospheric CO2 and other Greenhousgases (GHG) affect the incoming (from sun) and outgoing (from earth) radiation. I understand that at certain wavenumbers (or areas of wavenumbers) in the ...
2
votes
1answer
401 views

Does magnetised material lose weight?

I've had argument on a forum about this. People think, that: if the same object is magnetised, it has less energy. so by $E = mc^2$ it weighs less than an object that is not magnetised (hence spin of ...
1
vote
0answers
214 views

Macroscopic superposition of humans and past thoughts? [closed]

Decoherence apparently only works if a lot of degrees in the environment are measured with infinitely many copies reaching to all eternity. If too few memories and records survive with infinitely many ...
5
votes
2answers
162 views

Advice sought on choosing a camera for a Meade LX10

I have a Meade LX10 and have never done any astrophotography (except with some computerised SBIG ST9s on my university's LX200s). I would like to get started at home, but could do with some advice on ...
4
votes
1answer
191 views

Argument for quantum theoretic conformality of $\cal{N}=2$ super-Chern-Simon's theory in $2+1$ dimensions

I am using the standard symbols of $V_\mu$ for the gauge field, $\lambda$ for its fermionic superpartner and $F$ and $D$ be scalar fields which make the whole thing a $\cal{N}=2$ vector/gauge ...
0
votes
1answer
277 views

The acceleration of a particle in uniform electro-magnetic field

A particle of charge $q$ and mass $m_0$ is subject to the action of a uniform electro-magnetic field $\vec{E}=(0,E,0), \vec{B}=(0,0,B)$ and at $t = 0$ moves with velocity $\vec{v}=(v_1,v_2,v_3)$. ...
1
vote
2answers
1k views

Function of electric water pump

What is the function of electric water pump, i.e does it push or pull water or both?
2
votes
2answers
182 views

Reference for solid state particle detector

I'm looking for a good introductory text on solid state devices for particle detection. Thanks a lot.
27
votes
7answers
5k views

Why is the observable universe so big?

The observable universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
15
votes
1answer
663 views

Why is the universe map shaped like an oval?

I understand that the Mollweide projection is used to show the map of the universe. Although I understand how this projection can be interesting for Earth where most populated (and of interest) ...
7
votes
2answers
689 views

Finding Directions using moon

Is it possible to find directions just by looking at moon(not full bright)? I was curious to use the clue that if moon is half lit then the direction in which it is lit will it be east?
2
votes
2answers
896 views

Evaporation from a capillary tube

Consider a capillary tube (say from a liquid / capillary thermometer), that means a tube of small internal diameter which holds liquid by capillary action . The tube is fulfilled with water and closed ...
-1
votes
2answers
589 views

A fan in a hot room at what point does it put in more energy that it dissipates

If a fan that is using 50 watts is moving 1 m³/min of air. Lets say the walls are the same temperature as the air so there’s no heat dissipation there. How do I know if the fan is putting in more ...
15
votes
6answers
31k views

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 ...
3
votes
2answers
231 views

electron orbits

Is there an upper limit to the number of orbits an electron can have around say a proton? Arent there states that are unstable(for n!=1) with corresponding mean/half lives and therefore uncertainty in ...
1
vote
1answer
295 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 ...
3
votes
2answers
387 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?
7
votes
2answers
1k 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) = ...
11
votes
4answers
3k 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 ...
4
votes
1answer
477 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. 1) If we imagine the space station as a hollow doughnut ...
1
vote
2answers
2k 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 ...
11
votes
5answers
2k 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 ...
15
votes
6answers
2k views

Double light speed

Let's say we have $2$ participles facing each other and traveling at speed of light Let's say I'm sitting on #$1$ participle so in my point of view #$2$ participle's speed is $c+c=2c$, double light ...
9
votes
3answers
1k views

If you throw dynamite into a pool of lava, will it explode or melt?

I was playing a table-top rpg with a friend. It was set... well it was pretty weird, so I won't get into it. Suffice it to say the bad guy had a stick of dynamite and we were on a volcano. I hit the ...
19
votes
6answers
1k views

Can one do the maths of physics without using $\sqrt{-1}$?

The use of imaginary and complex values comes up in many physics and engineering derivations. I have a question about that: Is the use of complex numbers simply to make the process of derivation ...
1
vote
0answers
217 views

Presence Of an Another Universe [duplicate]

Possible Duplicate: Experimental evidence for parallel universes Is there an universe similar to ours somewhere else, I mean I had heard from Einsteins theories that,actually when I am ...
4
votes
2answers
579 views

Is the entire Universe the same age?

Is all of the visible Universe exactly the same age everywhere? What about the Universe beyond what we can see?
6
votes
1answer
30 views

Lack of exoplanet missions in the decadal survey

In recent exoplanet meeting "The Next 40 Years of Exoplanets", there was much discussion of the inablity of the community to agree on whether to support coronagraph missions or interferometer ...
2
votes
0answers
60 views

Degenerated Anderson Model Simulation

I'm trying to simulate the degenerative Anderson model. So depending on an energy difference first orbital and afterwards spin magnetism occurs. First i try to solve an easier ansatz with a limitation ...
0
votes
2answers
142 views

Space Interferometry Mission (SIM) cancellation [closed]

NASA's SIM mission was recently cancelled despite \$600 million being spent already over the last ten years. Has this \$600m been completely wasted or has any new technology been developed that could ...
0
votes
2answers
66 views

Study of exoplanets reaching saturation point [closed]

In recent exoplanet meeting The Next 40 Years of Exoplanets, it was mentioned a few times that the field/topic is becoming saturated. In what ways is it becoming saturated, and can you see the effect ...
6
votes
2answers
875 views

Why is BTZ black hole asymptotically $AdS_3$?

The metric for the BTZ black hole is $ds^2=-N^2dt^2+N^{-2}dr^2+r^2(N^\phi dt +d\phi)^2$ where $N^2=-M+\frac{r^2}{l^2}+\frac{J^2}{4r^2}$ and $N^\phi=-\frac{J}{2r^2}$. It is often said that BTZ black ...
4
votes
4answers
246 views

Could dark energy be the effect of gravity at great distances?

This may be a silly question, but is it possible that dark energy and gravity are related to each other? Space-time is deformed everywhere in space by objects with mass. The more massive the object, ...
5
votes
3answers
230 views

What does a planet look like in the infrared?

I've been trying to find a good source for what the planets look like in the infrared, specifically if viewed as a point source. I've been working with a low resolution telescope that senses in the ...
8
votes
3answers
621 views

Electrons in CRT

In a CRT, where do the ejected electrons go after they cause fluorescence on the screen, have they lost most of their energy, or do they actually go through the glass?
6
votes
2answers
1k views

Why did my liquid soda freeze once I pulled it out of the fridge?

Can someone explain in both layman's terms and also technically why when I pulled my glass filled with liquid soda from the freezer, the liquid soda quickly froze? Doesn't this violate the 2nd law of ...
1
vote
2answers
297 views

Running: Determine how much more energy is needed per extra kilogram of weight

(I recently asked this on maths but was directed here) I have recently become a runner and having a keen interest in kinematics I'm very interested in the maths/physics of my running. Can someone ...
2
votes
0answers
70 views

Complementarity between the laws of physics? [closed]

Is this following proposal plausible, worth considering, or dismissable as lunatic fringe science? What if the universe isn't really what we think it is but some universal quantum computer where we ...
-2
votes
1answer
578 views

How to simplify e to power of j.t [closed]

I have exam tommorow and cant get this figured out :( dont blame me but please answer this question. I Want to simplify this term: 3 times ((e topowerof 5jt) + (e topowerof -5jt)) Thanks.
16
votes
2answers
184 views

What is a “Trojan Moon”?

Today I read an article about Saturn's moon Helene, and it was described as a "Trojan Moon" but no further explanation was given. It was difficult to even get any context about the term from the ...
2
votes
1answer
304 views

How can I calculate how long to keep my beverage chilled?

The problem is simple, I suppose... I have a beverage at room temperature (let's say 23°C) in an aluminum can (it's a Barq's root beer.) I want to put it in a freezer (let's say it's at -17°C). How ...
5
votes
3answers
385 views

How to include random force in the simulation (Classical Molecular Dynamics)

I need to implement a random force in my code according to the fluctuation dissipation theorem. I have a Gaussian distribution function ready width average 0 and distribution 1 and I know I need to ...
1
vote
1answer
156 views

Non-Dimentionalization of equations

I am trying to understand a paper in which they mention; " We non-dimentionalize the problem hereafter by selecting mass, length and time units such that the fluid density $\rho\equiv1$ the ...
2
votes
3answers
148 views

Length of a curve in D dimensional euclidean space

In a book I am reading on special relativity, the infinitesimal line element is defined as $dl^2=\delta_{ij}dx^idx^j$ (Einstein summation convention) where $\delta_{ij}$ is the euclidean metric. Next, ...
3
votes
2answers
76 views

Color Variation in RR Lyrae

I've been doing some research on RR Lyrae stars and haven't been really able to find an answer to this question. RR Lyrae are well known for their periodic magnitude, and also are usually found in ...
1
vote
3answers
192 views

Constrained particles under distance dependent force

This question is from the 1975 Canadian Association of Physicists Exam. No solutions are posted and I am quite lost on how to proceed with it. A particle is constrained to move along the x-axis of a ...
14
votes
2answers
1k views

Has everything we see happened in the past?

Whatever we see is basically based on the light that hits our eyes, right? When we look at the Moon we are looking at the Moon as it was couple of seconds ago, as the light takes some seconds (~2 ...
5
votes
2answers
309 views

Small change in theta - polar coordinates

I'm reading (I'm trying to read) Schutz's "A first course in general relativity" (1985). On page 126 he mentions that a small change in angle theta in polar coordinates is given by: I can't see why ...
3
votes
2answers
513 views

Impact of gravity on bone structure [closed]

Some suggest that if a human was born and raised in a gravity-less environment their bone structure/strength would be different that for children born on earth. If this is the case do you think this ...

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