Proton falling into a Black hole?

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Discussion Overview

The discussion centers on whether a proton falling into a black hole would experience tidal forces and how these forces might affect its structure, particularly in the context of quantum mechanics and general relativity. Participants explore the implications of the proton's finite size and its wave-like properties, as well as the comparison to photons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that a proton, being a composite object with a finite size, would experience tidal forces that could distort its shape as it approaches a black hole.
  • Others argue that the effect of tidal forces on a proton would be negligible due to its small size compared to astrophysical black holes.
  • A participant questions how to quantify tidal forces in the framework of classical general relativity, particularly regarding the geodesic deviation equation.
  • There is confusion between protons and photons, with some participants discussing the implications of tidal forces on photons, although this is noted as potentially irrelevant.
  • One participant emphasizes that analyzing tidal stresses on a photon does not make sense due to its lack of internal structure and the absence of a comoving frame.
  • Another participant explains the need for multiple coordinates to describe an n-body system, using the example of quarks within a proton.

Areas of Agreement / Disagreement

Participants express differing views on the effects of tidal forces on protons and photons, with no consensus reached on the quantification of these forces or their implications in the context of black holes.

Contextual Notes

Participants acknowledge limitations in their understanding of quantum mechanics and general relativity, which may affect their interpretations and discussions. The discussion also highlights the complexity of comparing the behaviors of protons and photons in extreme gravitational fields.

cragar
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I don't know if this is the right place to post this but would a proton falling into a black hole experience tidal forces. If the proton is like a wave could we stretch the wave out, that is probably really bad wording. Or does the quantum of energy move all together?
 
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A proton is a composite object with quarks inside, and the proton has a size, about 1 fm=10^-15 m, which is essentially the typical distance between the quarks. In the frame of an observer hovering just outside the event horizon, the proton falls past at a velocity close to c, so that the de Broglie wavelength corresponding to its center-of-mass momentum is very short -- much shorter than the size of the proton itself. In a frame comoving with the proton, its de Broglie wavelength is infinite. Because a proton has a finite size, it would certainly experience tidal forces that would tend to distort its shape, i.e., cause the correlations among the quarks to change, probably giving it an ellipsoidal shape. However, tidal forces have less effect on smaller objects, and a proton is very small, so I think for any astrophysical black hole the effect would be much too small to measure.
 
bcrowell said:
Because a proton has a finite size, it would certainly experience tidal forces that would tend to distort its shape, i.e., cause the correlations among the quarks to change, probably giving it an ellipsoidal shape.
How would you quantify this tidal force in the framework of classical GR if at all since the equation of geodesic deviation is proportional to the four - velocity which is undefined for a photon?

EDIT: yeah...nevermind
 
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WannabeNewton said:
How would you quantify this tidal force in the framework of classical GR if at all since the equation of geodesic deviation is proportional to the four - velocity which is undefined for a photon?

Are you confusing proton and photon? The thread is about proton.
 
PAllen said:
Are you confusing proton and photon? The thread is about proton.

Wow that's embarrassing. I read it as photon. Thats what happens when I don't drink coffee.
 
No but it would be interesting to consider tidal forces on a photon.
@ bcrowell, How can you tell me a proton has a finite size if its wave.
If we can I would like to discuss how the tidal forces would effect the photon.
 
cragar said:
@ bcrowell, How can you tell me a proton has a finite size if its wave.

Mm...what's your level of background in quantum mechanics?
 
I have self taught myself a little bit about QM out of Griffiths . I know what a momentum operator is, Quantum harmonic oscillator . Spin matrices . But still a very elementary understanding of it. But I know a little bit.
 
cragar said:
have self taught myself a little bit about QM out of Griffiths . I know what a momentum operator is, Quantum harmonic oscillator . Spin matrices . But still a very elementary understanding of it. But I know a little bit.

OK, that's plenty. The idea is that if you want to describe an n-body system in one dimension, you need n coordinates. Those coordinates don't have to be just the x coordinates of each particle. For example, if your system consists of three quarks, A, B, and C, then you might want to take one coordinate to be the position X of the center of mass, one to be xA, and the third to be xB. The advantage is that the behavior of X is fixed trivially by conservation of momentum, so that simplifies the problem. The wavefunction in terms of X is simply a sine wave. The momentum P associated with X is the momentum associated with the center of mass motion.

So for example if you ask why an elephant doesn't have observable wave properties, the answer is that P is on the order of 103 in SI units, so the wavelength is on the order of 10-33 meters. The wavelength is a gazillion times smaller than the elephant itself.
 
  • #10
ok , thanks for explaining that .
 
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I thought a little more about the photon version, and I don't think it makes sense to analyze that one in terms of tidal stresses. It's not a bound system that can have internal stresses. And whereas in the case of the proton there is a natural frame of reference in which to measure its elongation (the comoving frame), there is no comoving frame in the case of the photon.

I think this is similar to a contrast that comes up in the case of cosmological redshifts. Photon wave-trains lengthen over cosmological time, and this can be interpreted in terms of the expansion of space itself as they travel through it. But protons, solar systems, etc., do not undergo any significant cosmological expansion.
 
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