All Questions
Tagged with particle-physics general-relativity
68
questions
2
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100
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Can squeezed vacuum reduce the mass of a black hole?
Could the negative energy density parts of squeezed light really reduce the mass of a black hole, as stated here (“A pulse of negative energy injected into a charged black hole might momentarily ...
- 135
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2
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645
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Can we regard metric as the Higgs field of gravity?
The longer version of the question is: should we regard special relativity just as a spontaneous symmetry breaking phase of general relativity, driven by the non-zero vacuum expectation value (VEV) of ...
- 4,452
1
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0
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45
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Does strongly gravitating object travel along geodesic of a background field？ [closed]
That test particles travel along the geodesic is assumed in the context of GR. But does it apply to strongly gravitating object, such as black hole in an expanding universe, binary neutron star, etc.? ...
- 619
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1
answer
116
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Energy spectrum in Klein-Gordon equation in general relativity
I know that the Klein-Gordon equation in general relativity takes the form (a massless field)
$\nabla_\mu \nabla^\mu \phi=\sum_{a,b} \frac{1}{\sqrt{-g}}\partial_a(\sqrt{-g}g^{ab}\partial_b\phi) =0$
...
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17
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6
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How can a grain of sand be "spaghettified" when nearing a black hole?
I have a hard time wrapping my head around this "spaghettification" process that apparently takes places when getting close to a black hole.
Gravity is proportional to the distance of the ...
- 439
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1
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51
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Equivalent theories of general relativity and graviton spin
Are there equivalent theories of general relativity that assume a graviton has a spin-1?
- 31
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0
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182
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How do I self-study physics at the undergrad level? [closed]
I'm a new physics undergrad worried that I won't be able to learn everything I want at the university I'm going to.
Basically the Institute I'm going to is applied sciences focused, and all electives ...
- 21
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0
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27
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Does photon energy affect deflection of a beam of light in a gravitational field? [duplicate]
Does photon energy affect deflection of a beam of light in a gravitational field?
According to general theory of relativity angular deflection of a beam of light in a gravitational field is
$$φ = \...
- 101
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0
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58
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Black $p$-brane solution
Im trying to confirm that the metric (11) in the paper below is a solution to Einstein's equations (6). I tried to use the metric and extract $\lambda=(1-(r_+/r)^{D-3})^{1/2-\gamma/2(D-3)}$ and $R=r(1-...
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0
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53
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Is there an upper boundary to magnetism?
This is gonna take some explaining, and full disclosure: I'm still undergrad, so please, forgive my ignorance here. Though please also hear me out: magnetism, like gravity, falls off with distance, ...
- 111
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60
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Evolving energy density of a particle species in cosmology
Suppose you have a momentum distribution of some decoupled $X$ particles in the early universe $f(\mathbf{p})$ that is injected in (well above the electroweak scale so that degrees of freedom for all ...
- 499
3
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1
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199
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Will the ever accelerating space expansion (like at the level of inflation) eventually break causality?
I have read this question:
requires that "for an action at one point to have an influence at another point, something in the space between the points, such as a field, must mediate the action&...
- 29k
-5
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1
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103
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Do objects with different sizes or masses experience time differently when they are moving in a constant velocity in their own reference frame? [duplicate]
My question is actually not about curve spacetime. Just curious if different mass affects how the object experiences time. Hope that someone can give a detailed explanation on this. Thank you!
0
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2
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118
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Does the mass of a moving object in empty space with a constant velocity change within its own frame of reference from its rest mass?
I believe that a constant velocity moving object in empty space within it own frame of reference retains its rest mass as long as it is moving at constant velocity and an effective mass increase ...
- 4,170
1
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2
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128
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Is $\frac{dE}{dt}=0$ in an accelerating particle’s instantaneous rest frame?
My special relativity book uses an argument that involves $\frac{dE}{dt}=0$ in an accelerating particles rest frame (to show a force parallel to a particles velocity is parallel in all frames).
...
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2
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2
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239
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Does an observer moving in a circle with constant angular velocity in space experience GR gravitational time dilation?
Assuming that there are no other planets or other gravitational sources around the observer in empty space, would the observer's very fast circular motion create GR gravitational or else called ...
- 4,170
5
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1
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342
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Why did Dirac say that atomic time is different from relativistic time, and that gravity is becoming weaker? What is the relation between the two?
In this gem of an interview in 1982 with Friedrich Hund, Dirac says at 09:17 that there is some theoretical basis and observational evidence that atomic time and distances are different from ...
- 1,421
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1
answer
84
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What happens when a galactic body gets bigger?
In my simple non-quantum non-nuclear but enthusiasm-filled mind, I fascinate that as a galactic body become much more massive, it can reduce matter first down to its building blocks, then eventually ...
- 137
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0
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110
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Why is the entry barrier in Physics Research Topics so high? [closed]
Why is the entry barrier in physics research so high?? When I try to read a research paper to see the latest developments in a particular topics I am always held back by my mathematical abilities. And ...
36
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7
answers
4k
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Why can’t gravitons distinguish gravity and inertial acceleration?
If gravitons mediate the gravitational force, couldn’t the detection of gravitons by an observer be used to distinguish whether they are experiencing gravitational acceleration vs. inertial ...
- 481
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1
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78
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Moving particle with GR not taken into account vs GR taken into account
If we imagine a lightwave moving through space without considering how the space is deformed due to the energy and momentum of the light, we would find it redshifted once we take GR into account ...
- 631
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0
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62
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Lagrangian of free particle relativistic case
Why must the covariant Lagrangian of a free particle be a first-order differential?
5
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1
answer
283
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The Explosive Force of the Braking Alcubierre Drive - What would this look like? [closed]
The Alcubierre Drive and faster than light travel more generally may be locked away in the realm of fiction forever. That might be depressing to some people but I think their impossibility is really ...
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1
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41
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Question about relative velocity and black hole formation in a fixed target experiment
In a given frame S, consider an inelastic collision between a particle A and a fixed target B. In frame S, the relative velocity of A (and thus the kinetic energy) to an observer in frame S is not ...
- 100
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1
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113
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Is there a way to detect gravitational waves in subatomic particles?
Consider the hypothetical situation of two electrons orbiting each other with a certain radius between them, going at extremely high speeds.
Would this create gravitational waves strong enough to be ...
user250721
-1
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1
answer
205
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Do particles produce gravitational waves?
We have obviously detected gravitational waves at very large scales, but what about small scales? I accept the answer that they would be indetectable, however I would think it would, considering the ...
user250721
2
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0
answers
180
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Spin particles in curved spacetime
On the Lorentz space, particles are axiomatized as unitary projective representations of the Poincaré group (according to Wigner if I recall correctly). It is then possible to specify a (non-charged) ...
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3
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202
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What is the result that that differs by many orders of magnitude between QM and GR? [duplicate]
It is well known that QM and GR are deemed incompatible due to a discrepancy in some calculations which I have read can differ by large magnitudes. What are these calculations to which people are ...
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1
answer
57
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What does the photon feel when it hits an asteroid on its path to earth [duplicate]
If a photon was approaching earth, after 1 minute(from earths reference frame) an asteroid comes on the photons path. And it hits the asteroid, but from the photons reference frame time doesn't pass ...
2
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0
answers
131
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Elementary particle (electron) and non-elementary (proton) spagettification
I understand that spagettification means the vertical stretching and horizontal compression of objects into long thin shapes in a non-homogenous gravitational field, it is caused by tidal forces.
Now ...
- 29k
-3
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5
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411
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What causes a single photon to divert its trajectory?
If a single photon passes close enough to a star, the gravity will diverts its trajectory. What causes a photon to divert its trajectory as it passes a sharp edge or the boundary of two mediums?
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6
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1
answer
205
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Spin statistical theorem in curved spacetime
In Wikipedia
https://en.wikipedia.org/wiki/Spin%E2%80%93statistics_theorem?wprov=sfti1
It states that
“The proof requires the following assumptions:
The theory has a Lorentz-invariant Lagrangian.
...
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1
answer
85
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Is the Large Number Hypothesis still a subject worth researching? [closed]
I've done some research on it for an essay competition of the Gravity research Foundation and shared it with other physicists but the response was very dismal in the sense that most physicists didn't ...
9
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2
answers
1k
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Why does gravity need a graviton? [duplicate]
Einstein theorized that gravity is a phenomena manifested by the curvature of spacetime, in effect it IS the curvature of spacetime. If this is so, why do we need a graviton to convey the force of ...
- 115
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1
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314
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Do we use any other kinds of affine connections in physics apart from the Levi-Civita connection?
When studying General Relativity, I learned that we use the Levi-Civita connection, i.e. torsion-less(or just symmetric) and compatible with the metric(the covariant derivative of the metric is equal ...
- 7,720
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1
answer
103
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Apparent analogies between statements from linear algebra and covariant tensor calculus
When using covariant tensors in relativity or particle physics, there are some statements that seem like analogues of statements known from linear algebra. For example, if we have a symmetric real-...
- 121
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1
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49
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On two different size planets occurs radioactive decay, is the amount of decay the same?
Imagine there is a planet as big as our sun and a earth like planet. On both planets is a box with equal amounts of radioactive polonium. In between the planets is a measure station. After 10 years ...
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7
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1
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307
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Are there any additional fundamentals of physics in addition to space-time, energy, mass, and charge?
What do you consider the fundamental quantities in physics to be? By fundamentals, I mean quantities that cannot be described by a combination of other quantities. Fundamentals are things that just ...
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0
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77
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does an accelerated charge would be slower relative to an neutral particle due to radiating and lose energy ? both in free fall
this part from this article https://en.wikipedia.org/wiki/Paradox_of_a_charge_in_a_gravitational_field
"Putting together these two basic facts of general relativity and electrodynamics, we seem to ...
4
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4
answers
1k
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Resource Recommendations: General relativity, local tetrads and particle physics
I'm still self-learning general relativity. I have been a huge fan of Andrew Hamilton's amazing lecture notes on GR, black holes and cosmology. He goes through GR in pretty much full tetrad formalism. ...
5
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1
answer
622
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Charge without charge and non-traversable wormholes
My question concerns the theory proposed in this classic paper by Misner and Wheeler. In the paper, the authors propose the idea of "charge without charge"--namely, that positive and negative ...
- 2,665
13
votes
2
answers
1k
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Do photons generate gravitational waves since they affect with their energy the stress tensor? [duplicate]
The gravitational waves are fact. They are produced in a way predicted 100 years before by Einstein. Anything with energy affecting stress tensor of space time produces them. What does it happen with ...
- 314
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vote
1
answer
435
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If a black hole is just warped spacetime, then where is the electric charge?
I've heard Kip Thorne repeatedly state that matter is destroyed when a black hole is created, that all you are left with is distorted spacetime.
"The idea that black holes are made from very ...
- 51
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1
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238
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Does an object traveling near the speed of light create a gravitaional field? [duplicate]
Does a particle traveling near the speed of light create an observable/measureable gravitational field around it? I know most elementary particles travel near the speed of light and have no ...
4
votes
1
answer
184
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If the effects of gravity cannot travel faster than the "c", does this mean we are only gravitationally bound by masses in our observable universe?
I'm 17 and fascinated by the differences and omissions Newton made in his equations of motion. However it makes sense that gravity can't travel faster than light because of the force-carrying photons.....
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1
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262
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What is the smallest amount of neutrinos needed to create a black hole? [duplicate]
Is there some smallest amount of neutrinos needed to create a black hole?
Note that this question is not at all the same as the question here If a 1kg mass was accelerated close to the speed of light ...
- 1,005
7
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3
answers
858
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Can the Unruh effect be confirmed by the LHC?
Two short questions regarding the Unruh effect. There are related answers on this forum and on wikipedia, but I am looking for confirmation of my own intuitive assumptions, so a straightfoward yes or ...
user74893
4
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1
answer
594
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Does accelerating generate gravitons?
If gravity and acceleration are indistinguishable, then does that mean converting potential energy to kinetic energy generates gravitons... but only temporarily until you stop accelerating?
- 463
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3
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372
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Particles Associated With Gravitational Waves
I've been reading about linearized GR and the study of gravitational waves, and an odd thought popped into my head. According to wave-particle duality (admittedly, usually used in quantum mechanics!), ...
- 10.8k
2
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1
answer
643
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Does a hydrogen atom today have same mass as a hydrogen atom in the future?
Does an atom of hydrogen today have the same rest mass energy as an atom of hydrogen a billion years in the future?
Standard cosmology seems to tacitly make this assumption.
But surely one can only ...
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