0
votes
1answer
6 views

Black-holes, space time and their bending

I have been watching some videos related to how space-time is bent because of the mass (just "visually", not mathematically), and then I watched some videos about black holes. My own conclusions ...
0
votes
0answers
15 views

Order of magnitude!

I'm having a hard time determining the order of magnitude for these quantities: Heartbeat: $93\,{\rm bpm}$ Mass: $93\,{\rm kg}$ Height: $1.75\,{\rm m}$
-2
votes
0answers
5 views

Converting the derivative into a particular form

I have found the derivative which is $$dy/dx = \frac{-2x(X+1)}{(X+2)^5}$$ however how would you express this derivative into the above form.
0
votes
0answers
31 views

is it possible to get “100% sure” physical/chemical measurements and/or “100% clear” compounds? [on hold]

The obvious question for any serious movie fan of the famed "Breaking Bad" series is, arguably, "is the chemistry setting (e.g. the famous "Heisenberg Purity") realistic at all?". The question itself ...
0
votes
0answers
4 views

Why does a system have to be holonomic?

So I'm doing some work from Taylor's mechanics book. He says for the problems in the book, we require the system is holonomic - that is the number generalized coordinates = number of Deg. of freedom. ...
0
votes
1answer
25 views

Rockets and distance

I am trying to create an equation which allows for me to change the aspects of the rocket so i can calculate the distance traveled vertically. My idea is for a rocket that only moves vertically; ...
1
vote
1answer
3 views

Relativity and Projective Geometry

How do you identify the cross ratio equation of projective geometry from the hyperbolic geometry of relativity? Specifically, what relativistic variables would correspond to A,B,C,D in the standard ...
0
votes
0answers
3 views

Path length difference from multiple sources?

I know that path length difference is given by the difference in the distance from each source to the observer, but I feel like this doesn't apply when some of the distances are the same, like in the ...
-1
votes
2answers
17 views

Why is there a universal speed limit

I am looking for an answer that does not rely on Special or General Relativity -and without recourse to the fact that the speed of light is frame invariant. Is there another way of showing this ...
-2
votes
0answers
15 views

if potential function is given for free space , how to find total charge on a conductor placed there?

Consider the following potential function in free space: $$V = \frac{100xz}{(x^2 + 4)}$$ If the $z = 0$ surface is a perfect conductor then find the total charge on that portion of the conductor ...
3
votes
4answers
89 views

How to determine the observables rigorously?

In Quantum Mechanics, as I know, if a system is described by a Hilbert space $\mathcal{H}$, each physical quantity is associated with some hermitian operator $A : U\subset \mathcal{H}\to \mathcal{H}$ ...
0
votes
1answer
195 views

Difference between directional and omnidirectional transmission or reception?

It is suggested that the next generation wireless technology will be highly directional since this increases the signal gain (MIMO) and decreases interference. How will the receiver still be able to ...
1
vote
1answer
39 views

Does charge conjugation affect parity?

Notice that these transformations do not alter the chirality of particles. A left-handed neutrino would be taken by charge conjugation into a left-handed antineutrino, which does not interact in ...
1
vote
3answers
374 views

What is the meaning of spin two?

As the title suggests, what is the meaning of spin two? I kind of understand spin half for electrons. I can kind of understand spin one for other particles. However I'm not sure how something could ...
0
votes
2answers
78 views

Understanding the Bloch sphere

It is usually said that the points on the surface of the Bloch sphere represent the pure states of a single 2-level quantum system. A pure state being of the form: $$ |\psi\rangle = a |0\rangle+b ...
3
votes
1answer
36 views

The effect of relativistic near misses

Alice and Bob are both floating in free, empty space. Alice does not like Bob very much. Thus one day, believing that there is no such thing as overkill, Alice takes her programmable hyper-energetic ...
-1
votes
0answers
9 views

Could dark matter be the result of gravity fields disrupted by the non-uniform expansion of dark energy?

Specifically, I am wondering if dark energy (the expansion of space) is emitted from the center of our galaxy causing gravity to appear weaker at the center of our galaxy relative to the area known as ...
2
votes
1answer
90 views

Why does ice melts faster near the surface of water?

I had a few frozen bottles and while they were melting I saw this: in all of the bootles, the ice seems to get thiner near the surface. I have searched a bit and I've found this video that shows ...
0
votes
1answer
15 views

Why do spiral waves annihilate each other when 2 wavefronts collide?

I was reading about Fitzhugh-Nagumo model. And in a 2D space the simulations a Reaction-Diffusion process associated with FitzHugh system look like this. But intuitively I could not satisfy myself ...
0
votes
2answers
33 views

Are known (“old”) elements being made synthetically using fusion?

Are known ("old") elements being made synthetically using fusion? I hear about research about making new heavy elements, but type "making known elements" on Google and nothing comes up. Are any known ...
3
votes
2answers
129 views

Could the singularity that gave rise to our universe be past-eternal?

Are there any compelling models that include a past eternal singularity that ultimately gave rise to our universe? Does the "no-boundary" hypothesis that utilizes imaginary time have past eternal ...
13
votes
1answer
894 views

If two ultra-relativistic billiard balls just miss, will they still form a black hole?

This forum seems to agree that a billiard ball accellerated to ultra-relativistic speeds does not turn into a black hole. (See recent question "If a 1kg mass was accelerated close to the speed of ...
3
votes
4answers
254 views

Is uncertainity a postulate?

I heard the standard interpretation of Heisenberg Uncertainty Principle: Just the measurement affects the position of the body because always you want to see a body (=to measure the position), you ...
4
votes
1answer
101 views

Why is a relativistic quantum theory of a finite number of particles impossible?

In Dyson's book Advanced Quantum Mechanics , he said "These two examples (the discovery of antimatter and meson) are special cases of the general principle, which is the basic success of the ...
-1
votes
2answers
37 views

Can a pilot in a small spaceship feel G force in space?

I am not really good in physics so I might be wrong on some points, but here is the situation. Consider a spaceship the size of a fighter plane. And like a fighter plane, the ship is very mobile. The ...
0
votes
0answers
12 views

can I electrify a pin by applying current in its base?

I imagine electric circuits as loops. So I wonder, if it is possible to electrify a pin but not connecting its two edges, instead only applying current at its base. But I want the current to run ...
4
votes
2answers
43 views

Are orbits possible in de sitter space?

Since the de sitter space has constant positive curvature does that mean that objects can't orbit around other objects?
1
vote
3answers
173 views

Strain and stress tensor

I have problem by definition of strain and stress. From Gockenbach's book that our reference for FEM, we have $$\epsilon=\frac{\nabla u+ \nabla u^T}{2},$$ that $u$ is vector displacement, and ...
1
vote
2answers
35 views

Would a magnetic needle standing on it's point on a magnet be more stable than the same needle stood on a non-magnetic surface?

So I was watching MinutePhysics' video 'How long can you balance a pencil?' and it turned out to not be for very long. Would introducing a magnet to the equation make for different results? We can ...
0
votes
2answers
110 views

Magnet dimensions for 3-phase permanent generator

I'm making a 3-phase permenant generator. According to Faraday's law, the emf produced is negative number of turns times the change in magnetic flux over the change in time. If it is only the CHANGE ...
0
votes
1answer
85 views

What is the baryonic mass distribution of the Milky Way

There are many, many studies of the Dark Matter halo around the Milky Way but I'm having trouble finding good raw data about visible matter. I'm investigating a MOND like model and would like some ...
1
vote
0answers
10 views

what is thermophoresis?

I read wikipedia article and I saw a bad youtube presentation on thermophoresis, however I don't have a clear insight about the subject. I assume the forces are basically brownian molecular forces ...
0
votes
0answers
11 views

Can an excited nucleus capture a second neutron?

I am wondering if is it possible to have the following scenario: Nucleus captures neutron. Nucleus is excited but does not relax through decay but captures another neutron. Maybe it is possible if ...
0
votes
1answer
39 views

Relation between area elements in finite deformation theory (continuum mechanics)

There are relations for the line and volume elements in continuum mechanics. For example: \begin{align} \ \ \ \ \ \ \ \ \ \ \ \ \frac{V}{V_0}&={\rm det}(F)\tag{1}\\ \lambda^2&=(F^TFe_1\cdot ...
1
vote
1answer
33 views

Book with solved problems on thermodynamics

I am working on honing my engineering thermodynamics problem solving skills at the undergraduate and graduate level. It would be much help if you could suggest me some good books with solved ...
3
votes
0answers
15 views

Is the right-handed antineutrino the CPT conjugate of the left-handed neutrino?

I am working from the book Massive Neutrinos in Physics and Astrophysics by Mohapatra and Pal (which is available here). On page 66, the authors claim that $\psi_{L}$ is the $\mathcal{CPT}$ conjugate ...
0
votes
1answer
11 views

Thermal Imaging reflection?

I was viewing a youtube video that was about thermal imaging and saw something that caused me to ponder but I couldn't figure out an answer and the one assumption I have I don't know if it's correct. ...
1
vote
1answer
219 views

If direction of torque is upwards(or downwards), why does the body rotate perpendicular to the direction?

We know torque is given by $$\vec{\tau} = \vec{r} \times \vec{F}$$ . Its direction is given by right-hand rule which says that torque acts perpendicular to the plane where force applied and position ...
9
votes
12answers
34k views

Why does the gas get cold when I spray it?

When you spray gas from a compressed spray, the gas gets very cold, even though, the compressed spray is in the room temperature. I think, when it goes from high pressure to lower one, it gets cold, ...
0
votes
2answers
197 views

Drift Speed and Current in Two Different Inertial Frames

We have a long, cylindrical wire carrying a constant current I in an inertial frame. At a distance of R from the center of the wire, the magnitude of magnetic field is $μI/2πR$. What is the magnitude ...
1
vote
2answers
63 views

Entanglement and coherence

I have come across a wonderful review of entanglement by Chris Drost in his answer to this post. One part that left me puzzled was: (This post is merely an attempt to understand a portion of Chris' ...
-1
votes
0answers
18 views

Practical uses of superfluids

I am wondering whether and how superfluids (possibly at room-temperature, if that is possible at some point) can be of any practical use in mechanical or electrical engineering or other fields. I ...
2
votes
2answers
54 views

The action of a relativistic point particle, the meaning of its parametrization invariance and possible potential terms

i am currently toying around with the behaviour of a classical relativistic point particle a bit. For a free one we get the action \begin{align} S =\int_\tau - m\sqrt{- \dot X_\mu \dot X^\mu}. ...
5
votes
4answers
163 views
+50

How is Liouville's theorem compatible with the Second Law?

The second law says that entropy can only increase, and entropy is proportional to phase space volume. But Liouville's theorem says that phase space volume is constant. Taken naively, this seems to ...
2
votes
1answer
239 views

Eigenstates of a density matrix of continuous variables

Consider a system of two entangled harmonic oscillators. The normalised ground state is denoted by $\psi_0(x_1,x_2)$. The reduced density matrix of the second oscillator is given by: $$\rho_2 = ...
4
votes
1answer
284 views

Is the cosmic microwave background radiation red shifted?

My question is. If the cosmic background radiation is red shifted how would you calculate the wavelength at the time it was emitted ?
2
votes
1answer
115 views

Kinematics of Euler angles relative to a rotating frame

I have a rotating body $B$ and a rotating frame $F$ whose orientations are described by the quaternions $q_B$ and $q_F$ respectively. I also have the angular velocity vectors $\omega_B$ and ...
0
votes
3answers
104 views

Forces Create Angular Acceleration And “Straight” Acceleration - But How Much Of Each?

Let me set up the following problem for a rectangle floating in space: We know its dimensions. We know its mass. There's a force pushing it for a known amount of time - we know the angle & ...
3
votes
1answer
71 views

Why complexify in order to construct Dirac representation?

Suppose we have a theory is covariant under the Spin group Spin(2n-1; 1). We consider the real vector space $V = R^{2n-1,1}$, which naturally comes with a Lorentzian inner product. On this vector ...
2
votes
1answer
28 views

Does every force which seems to have no effect cause a deformation?

The example in our discussion was: If I glue a peanut to the ceiling, does the ceiling bend? Some people argued that it wouldn't because ceilings do not bend for peanuts. Some people argued that the ...

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