10
votes
1answer
235 views

Computability of physics

As far as I understand a Universal Quantum Simulator can simulate any quantum system and thus anything that exists in the universe. Also, a quantum computer can implement such a quantum simulator. ...
3
votes
3answers
704 views

Why does an airplane need to climb during a takeoff even if it is in emergency situation?

Right after take-off (which means an airplane already exceeded V1) it is recommended that an airplane keeps climbing even when emergency occurs. Beside worries of crashing into houses and buildings by ...
2
votes
2answers
245 views

What Pauli matrices should I use for this two spin system?

Consider the Hamiltonian $H = -J_\text{F}S^{(1)}_zS^{(2)}_z + J_{AF}S^{(1)}_zS^{(2)}_z$, describing the graph Here, F means ferromagnetic and AF means antiferromagnetic interactions. I am having ...
3
votes
3answers
352 views

Power laws and deterministic systems

I am facing the following question. It is well known that power laws arise in many situations in nature. They arise even in thats physical systems that are completely deterministic (e.g. sand piles). ...
1
vote
1answer
239 views

Renormalization: Why is only a finite number of counter-terms allowed?

I have a question please about renormalization in QFT. Why a renormalizable theory requires only a finite number of counter-terms?
1
vote
2answers
196 views

Do Nuclear Power Plants have shutdown and cooling systems protected from a nuclear generated EMP?

Forty years ago, I read a report concerning the difficulties of protecting my companies equipment, which was to be installed in Air Force One, from a Nuclear EMP. An EMP generated by a high altitude ...
2
votes
2answers
142 views

When does $T^{ij} = T_{ij}$?

Suppose we have some tensor with components $T^{ij}$. Then suppose that we also have $T_{ij}$. When would $T^{ij}T_{ij} = (T^{ij})^2 = (T_{ij})^2$?
2
votes
2answers
130 views

Flux Over a Surface

I am teaching a multivariable calculus course and we are starting to go over surface integrals. I am a math professor with little knowledge of physics. At one point the book discusses fluid flow. ...
2
votes
2answers
260 views

What properties are entangled in quantum entanglement?

When two particles are entangled, one can measure the properties of one of the particles and instantaneously know the properties of the other. This is because the two particles possess the same ...
4
votes
2answers
1k views

Where does the energy of a lightning strike go?

Lightning contains a lot of energy, so where does this energy go after lightning has hit the ground? Does it travel all the way to the core? What happens after that?
4
votes
2answers
387 views

Field operator in Schrödinger picture

In Schrödinger picture operators do not depend on time explicitly. Consider a free scalar field with Lagrangian density $${\cal L} ~=~ \frac{1}{2}\partial_{\mu} ...
0
votes
1answer
1k views

Mutual Inductance and the Dot Convention

Can anyone please explain me, the dot convention in coil systems (Mutual and self inductance) with some related images to understand..?
1
vote
2answers
917 views

What is the physical or mathematical meaning of the Gibbs-Duhem equation?

The Gibbs-Duhem equation states $$0~=~SdT-VdP+\sum(N_i d\mu_i),$$ where $\mu$ is the chemical potential. Does it have any mathematical (about intensive parameters) or physical meaning?
-1
votes
2answers
3k views

What is the limit to how many satellites can orbit the earth?

I would like to know how many satellites are physically able to be in place, at the same time, orbiting the earth. Lets ignore which Nations need or use the most satellites (area in space above them) ...
0
votes
1answer
324 views

Nonuniform circular motion

A ball rocks around an arc. In the following illustration, the ball reaches the end of the arc (its velocity magnitude is zero at that particular moment). Now, I want to know which forces are ...
11
votes
3answers
2k views

Schrodinger's equation (explanation to non physicist)

For a report I'm writing on Quantum Computing, I'm interested in understanding a little about this famous equation. I'm an undergraduate student of math, so I can bear some formalism in the ...
1
vote
2answers
103 views

What fraction of peak horsepower do typical 4 door passenger vehicles use?

I was surprised when I looked at the power rating of the engine used on a Humvee. It's only ~190 horsepower, which is exceeded by many sedan engines. So an obvious question is why doesn't my Camry SE ...
1
vote
2answers
599 views

In the diode equation, why the exponential $\exp$ and the ideality factor $n$ are there? What do they represent & what is their significance?

In the Shockley diode equation, why the exponential $\exp$ and the ideality factor $n$ are there? What do they represent & what is their significance? I have to work on Solar Photovoltaics, and ...
6
votes
1answer
416 views

Is there any uncertainty between mass and proper length or time?

I was trying to naively draw a parallel between special relativity and the Heisenberg uncertainty principle. I try to understand uncertainty principle as a consequence of 4-position and 4-momentum ...
3
votes
1answer
77 views

What is the furthest object from which fermion rays were detected?

What is the furthest object from which non-electromagnetic cosmic rays were detected?
0
votes
0answers
63 views

is there an error in this paper ¿¿

http://vixra.org/pdf/0908.0079v1.pdf see equation (2.21) the reasoning to get this (2.21) goes from page 9 to page 14 should be the inverse of the potential denoted by $ x(V) $ proportional to the ...
0
votes
1answer
78 views

Quantum Chemistry Kronecker Delta formality

In semi-empirical quantum chemistry, one frequently encounters the so called zero differential overlap approximation $$\langle \mu \nu | \lambda \sigma \rangle = \delta_{\mu\nu}\delta_{\lambda\sigma} ...
0
votes
1answer
80 views

Melting ice pattern

What causes ice to melt in these patterns? And why does this always happen when the ice is covered in snow?
2
votes
2answers
129 views

Is it possible to record the 'blue air" effect when a core goes critical?

I've been studying about radiation, and I saw something called the Demon Core. Apparently, it was a core that was under experimentation by the government in Los Alamos to see the exact point at which ...
2
votes
4answers
607 views

Will the earth never cool, but only get hotter?

Since the earth is in a vacuum and therefore there is no thermal transfer of heat to anything else, how can it even cool down? It seems like its average temperature would always be constant, ignoring ...
18
votes
3answers
71k views

Virtual vs Real image

I'm doing magnification and lens in class currently, and I really don't get why virtual and real images are called what they are. A virtual image occurs the object is less than the focal length of ...
2
votes
1answer
158 views

Atomic physics through classical resonance?

I have a rather general question regarding the theory of Quantum Mechanics. To preface this question, consider a violin string. When a violinist exposes the string to a bow, this is exposing the ...
5
votes
1answer
622 views

Bohmian loophole in PBR-like theorems

I'm reviving and expanding this question, because of the new paper today, by Aaronson et al. The more general question is: How does quantum-potential Bohmian mechanics relate to no-go theorems for ...
3
votes
2answers
73 views

Wire morphing shape?

Can one morph a wire by electrical current into a shape different than static shape at beginning? As in the beginning shape being in a spiral, then when electrical energy is passed through the wire it ...
4
votes
1answer
433 views

How is the equation of motion on an ellipse derived?

I would like to show that a particle orbiting another will follow the trajectory \begin{equation} r = \frac{a(1-e^2)}{1 + e \cos(\theta)}. \end{equation} I would like to do this with minimal ...
0
votes
0answers
50 views

Should a 1D Guassian wave oscillate?

I wrote a few lines that numerically solve Maxwell's equations. The result is a moving wave that looks like a single pulse. This looks strange to me because I expect waves to move in oscillator ...
4
votes
2answers
163 views

What happens to this potential energy?

Let's say I turn on a Van de Graaff which creates a large positive charge. Now let's say I have an object with a positive charge in my hand and I start walking toward the Van de Graaff from $x$ meters ...
3
votes
2answers
522 views

Space Quantization of Quantum Angular Momentum

I am trying to understand what my book is trying to convey. Quantum angular momentum is $L_z = m_l \hbar$ "Choosing arbitrarily a z axis and using an appropriate experimental technique, we measure ...
2
votes
1answer
78 views

Tensor perturbation inflation

During inflation the metric is de-Sitter so $dt^2-d\underline{X}^2 $. I know that the eqn.motion governing GW's from inflation (tensor perturbations) is $$2H\dot{h}+\ddot{h}-\nabla^{2}_{i}h~=~0,$$ ...
3
votes
1answer
179 views

Is Hamilton-Jacobi equation valid for only conserved systems?

From derivation of Hamilton-Jacobi (HJ) equation one can see that it is only applicable for conserved systems, but from some books and Wikipedia one reads the HJ equation as ...
0
votes
2answers
110 views

A tensor summation question

With the definition of the tensor \begin{equation} J_{ij} = I_{ij} - \tfrac{1}{3}\delta_{ij}I^{k}_{k}. \end{equation} I have seen the quantity \begin{equation} J_{ij}J_{ij} \end{equation} written as ...
8
votes
1answer
270 views

Is this field redefinition for free scalar field theory non-local?

The action of free scalar field theory is as follows: $$ S=\int d^4 x \frac{\dot{\phi}^2}{2}-\frac{\phi(m^2-\nabla^2)\phi}{2}. $$ I have been thinking to redefine field as ...
3
votes
2answers
394 views

Quantum Teleportation Fidelity

I understand that quantum teleportation fidelity is the overlap of the initial quantum state with the teleported quantum state. If the teleportation is perfect, then the fidelity would equal 1 or 100% ...
2
votes
3answers
2k views

Expressing a unitary operator in terms of a Hermitian operator

In the context of unitary transformations as a change of basis in Hilbert space, Gottfried and Yan wrote in their book on quantum mechanics that expressing a unitary operator $U$ in terms of a ...
1
vote
2answers
264 views

Can't find the mass scale; calculation using the modified minimal subtraction scheme and dimensional regularisation

I am taking a course on quantum field theory where there is some confusion regarding the renormalisation scheme we are using (and a corresponding one in my mind). Apparently the lecturer meant MS-bar ...
3
votes
0answers
134 views

POVM advantage in state discrimination

Suppose we are given the task of discriminating, with minimum error, between a set of states $\{|\psi_1\rangle,|\psi_2\rangle,\ldots,|\psi_N\rangle\}$. In other words, we are given an unknown state ...
0
votes
2answers
220 views

What are hidden variables exactly?

What are hidden variables in quantum mechanics? I am aware there are many types but what exactly do they mean or even "do" exactly? Do they mean that the quantum indeterminacy becomes hidden but ...
3
votes
1answer
2k views

How much energy would it take to blow up the earth?

There is a common statement running around that we as a species has enough nuclear weapons to blow up the earth several times over. What I want to know is: by how many orders of magnitude is that a ...
3
votes
1answer
201 views

What algorithms are used for track reconstruction in cloud chambers?

In particular I'm interested in any algorithms that can separate multiple tracks from one another reliably.
1
vote
0answers
31 views

How do I find the force from drop shock using material properties?

I am dropping a cylindrical cast iron bar with a know elastic modulus and poisson's ratio, $E_{1}$ and $v_{1}$, onto a flat beam of elastic modulus, $E_{2}$ and $v_{2}$ so there is tangential drop ...
6
votes
1answer
246 views

Database of scattering amplitudes

I want to check whether my result for the invariant amplitude of the electron-electron scattering (to lowest order in $\alpha$; t+u channels) is correct or not. I can't find any reference that has ...
12
votes
3answers
1k views

What are the details around the origin of the string theory?

It is well-known even among the lay public (thanks to popular books) that string theory first arose in the field of strong interactions where certain scattering amplitudes had properties that could be ...
4
votes
4answers
2k views

Can an object between two magnets reduce their attraction/repulsion?

If you have two magnets (not in contact) and then put a non-magnetic object in between the two magnets, does that decrease the attraction/repulsion between the two magnets? It seems that it wouldn't, ...
4
votes
3answers
3k views

Are two waves being in phase is the same as saying that the two waves are coherent?

If two waves are coherent, is it the same as them being in phase? Please correct if I'm wrong.
1
vote
1answer
339 views

How do we know space is expanding when we are part of space? [duplicate]

From what I understand space itself is expanding, and the Big Bang attempts to describe this expansion at the very early stages of the universe. This is usually described in a visual way as 2 dots on ...

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