Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: qazibasit on 27/05/2005 17:42:39
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well i was thinking about the sound waves and i was thinking whether sound waves can escape from the black hole coz it is not particle in nature like the light waves.
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sound waves do appear to be made up of particles in the same way as light waves are, they are called phonons.
Remember a sound wave has to move through a medium and if that is moving towards the black hole fast, the sound wave won't get out. Basically if light can't get out nothing can - pretty much
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Here'a a Java applet showing it in action:
http://dept.kent.edu/projects/ksuviz/leeviz/phonon/phonon.html
The only radiation that in theory can leak out of a black hole aka Hawking radiation is actually a virtual pair of particles created at the edge of the black hole of which one is sucked into the black hole, but the other escapes as radiation. If you'd have to start at the bottom of the black hole there is supposedly no force in this universe that could lift anything out, be it particle or a message in a bottle.
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)
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sound waves do appear to be made up of particles in the same way as light waves are, they are called phonons.
Wow, never heard of that one. It's good to learn new things everyday. Probably I would prefer "Phonon" as the counterpart of "Photon"-archetype instead of "Tachyon" in Yu-Gi-Oh! ZeXaL.
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I have probably answered my own question has a rotating black hole a magnetic field ?, I would think not as the magnetic field is mediated by virtual Photons that cannot escape.
But the black hole could have formed from a highly magnetized Neutron star which had acquired additional mass from an orbiting star I which case what happens to the magnetic field that contains a lot of energy.
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well i was thinking about the sound waves and i was thinking whether sound waves can escape from the black hole coz it is not particle in nature like the light waves.
But sound waves need a medium in which to propagate. The sound wave itself consists of movement in the particles of that medium. Particle A bumps into particle B, allowing the sound to travel through the medium. There is no way for a particle inside the event horizon to bump into a particle outside of it, as that would require the particle to cross the event horizon.
So no, sound (or anything else that carries information) cannot escape a black hole.
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I have probably answered my own question has a rotating black hole a magnetic field ?, I would think not as the magnetic field is mediated by virtual Photons that cannot escape.
know very little about electricity (shocking admission), but my understanding is that a BH can be said to have mass, spin and charge. If it has charge, would this not mean it has an electric field?
The question is about a rotating BH. A rotating electric field creates a magnetic field (?).
So, a rotating BH has a magnetic field. I suspect this could not be detected from outside the EH, as this would mean that information was escaping from within the BH. (?).
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While sound can't escape from a black hole, the supernova that is happening around the forming black hole certainly makes a loud bang (if you were close enough, but not too close!)
If you view a black hole at rest in your frame of reference: A magnetic field can't escape from the black hole, but as Syphrum says, a pre-existing magnetic field from a neutron star will generate radio waves that propagate outwards at the speed of light, detectable as a pulsar. The near-field magnetism remains fairly close to the black hole; I imagine that this magnetic field would decay once the neutron star collapsed into a black hole.
If you view a charged black hole moving at relativistic velocities relative to you: You would view the electric field as having a magnetic component. According to my simplistic understanding, the electric and magnetic fields are aspects of the same field, and the characteristics change depending on the relative velocity of the observer.
But I expect that a charged black hole would not last very long, as it would attract the opposite charges more than it attracts like charges; this is the same reason that black hole progenitors are unlikely to be charged.
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It's weird though.
where is the charge located in a spinning bh?
Outside the event horizon?
To exist on the outside of a event horizon it must be, right?
(hmm, sounds like Yoda is involved there)
Otherwise we will have charge and gravity escaping, not only gravity.
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Otherwise we will have charge and gravity escaping, not only gravity.
That is exactly right.
If the Sun magically turned into a black hole (without going supernova), the Earth's orbit would not be affected. This is because the Sun's gravitational field extends to 8 light-minutes away (where the Earth is), and even beyond, "to infinity" (well, around 5 billion light-years, anyway). The source of this gravitational field has been compressed to a zero size, according to classical Einstein (although we couldn't explore within 3km of it, due to the event horizon).
Similarly, if the Sun had a significant electric field, this would also extend to 8 light-minutes away (where the Earth is), and even beyond, "to infinity". This external electric field is not affected by the collapse into a back hole. The source of this electric field has been compressed to a zero size, according to classical Einstein (although we couldn't explore within 3km of it, due to the event horizon). If it is truly a zero size, then its spin won't produce a magnetic field.
However, Einstein's now-classical theory does not take quantum effects into account, so we don't really know what would happen if we put a spinning, charged black hole into a supermassive MRI machine...
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Interesting Evan. Tried to see what charge was but the closest I got to it was ghopers chasing ghopers :) Should be on the site somewhere. Actually it reminds me of the idea of phonons and 'photons' propagating inside glass. The photon doesn't so much propagate inside it as it is 'reinvented' by energy transitions, if I now get it right :)
Makes phonons just as real as photons actually, thinking that way. Although : " If it is truly a zero size, then its spin won't produce a magnetic field." on what do you base that statement?
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" If it is truly a zero size, then its spin won't produce a magnetic field." on what do you base that statement?
I am a bit out of my depth here, since I never studied tensors, and I think the answer is buried in the component of Maxwell's equations commonly known as "Ampere's Law". You calculate it with line integrals and surface integrals, which I haven't touched since university :(
So maybe someone else can help here...
In my simplistic understanding:
- An electric current (in Amps) consists of an electric charge (in Coulombs) flowing through a wire in a certain time (in seconds)
- This electric current produces a magnetic field
- If a charge were distributed over the surface of the Sun (without blowing the Sun apart), then the rotation of the Sun will produce a magnetic field. The Sun acts as a virtual wire, carrying current past your measurement point.
- But if the charge is compressed into zero space at Einstein's black hole singularity, then no current can pass your measurement point, and the singularity does not act as a virtual wire, and it does not produce a magnetic field.
Of course, Hawking showed that quantum effects must occur near a black hole, so the real behavior may be a bit different from Einstein's non-quantised singularity.
See: https://en.wikipedia.org/wiki/Ampère%27s_circuital_law
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Thanks Evan, I do understand the difficulties here but still? Am I getting it right? Are you suggesting that a Black hole, if we now define its 'center' to be everywhere inside a event horizon can't carry a charge?
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the way I understand a 'center' is that they all are equivalently vanishing, (no matter what mass/size we define to it) which I think is the equivalent to your saying of 'zero space'. The point I'm using is the idea of a black hole having no center, instead allowing it all to be a center.
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a Black hole, if we now define its 'center' to be everywhere inside a event horizon can't carry a charge?
Quite the contrary. I was suggesting that the charge is concentrated at the singularity at the center of the black hole.
- To someone outside the event horizon, the charge may as well be at the surface of the event horizon
- To someone entering the event horizon of a supermassive black hole, they would not notice anything special as they pass the event horizon, and they would still see the charge "ahead" of them, closer to the center
- But of course, the twisted spacetime inside a black hole makes concepts like "ahead" somewhat equivocal..
Some aspects of the singularity:
- The finite charge of the progenitor star would be compressed into zero radius, producing an infinite electrical field gradient at the singularity, which I think means an infinite voltage.
- The finite angular momentum of the progenitor star would be compressed into zero radius, producing an infinite angular speed (as an angle), but over a zero radius
- Does this mean that the velocity is zero or infinite, or somewhere in-between? (ie it needs more information...)
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sound waves do appear to be made up of particles in the same way as light waves are, they are called phonons.
My understanding is that phonons are quanta of lattice vibrations, characteristic of collective excitations in an elastic arrangement of atoms or molecules in condensed matter, like solids and some liquids, as well as sound waves.
Possibly, they could be considered as "quasiparticles" - quanta of energy, but equating their to relationship to sound waves with the photon/light relationship seems a step too far.
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You know Evan, you make charge just as weird as I found it, chasing ghopers :)
Also, at a first glance, charge seems disconnected from the way we think of gravity?
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Not really Bill. If you think of how we define photons, they seem no less unreal than phonons. They don't 'exist', until a change
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When you want to 'shoot' single photons you have to be very specific in your experimental setup. And if you then 'allow' the environment you're in having a role, setting up the experiment, I would expect you to have to change your 'limits' aka how you define the experiment. But I don't think the photon agree to that, because I don't think it's limited by your experiment, it's there anyway. But yea, I had a lot of problems with phonon's too.
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When it comes to sound you normally need a medium for it to carry. When we speak of the universe creating 'sound imprints' of, f.ex the 'Big Bang', I don't think that holds. It's momentum, isn't it?
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Possibly, phonons could be considered as "quasiparticles" - quanta of energy, but equating their to relationship to sound waves with the photon/light relationship seems a step too far.
Phonons need a medium to propagate, and the stiffer that medium, the faster they propagate.
Sound can also propagate through a gas/plasma, but high frequencies are attenuated more in low-density gases; sound can't propagate if the wavelength is less than the mean free path.
Near a stellar-mass black hole, solids are ripped apart, blocking high speed transmission through a dense medium. The resulting dust and gas is then rarified (spaghettified), as the closer parts accelerate away from the farther parts.
But at the event horizon, the escape velocity exceeds the speed of light, and no medium can travel faster than this, and no sound can escape.
My understanding is that phonons are quanta of lattice vibrations
Phonons play an important role in Type 1 Superconductors - they are the force that binds together electrons (Fermions) into Cooper Pairs (effectively a composite Boson).
It is only when the temperature gets sufficiently low, when random vibrations of the medium are reduced, so that they don't disrupt the Cooper pairs.
See: https://en.wikipedia.org/wiki/Superconductivity#Conventional_theories_(1950s)
oops... overlap with yor_on
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Phonons need a medium to propagate, and the stiffer that medium, the faster they propagate.
Sound can also propagate through a gas/plasma, but high frequencies are attenuated more in low-density gases; sound can't propagate if the wavelength is less than the mean free path.
Let’s check if I have this right.
Light doesn’t need a medium, so it can propagate in an absolute vacuum (if it can find one).
The longer the mean free path, the faster light can travel, in the RF of an observer.
Sound requires a medium, so it cannot travel through a vacuum, even a partial vacuum.
Sound can travel through a medium if the mean free path is equal to (?) or shorter than the wavelength of the sound.
Eg. Sound cannot travel through interstellar space, because no sound has a wavelength that comes anywhere near the 1012, or so, LY that would be the mean free path in interstellar space. (Or would that be intergalactic space?)
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Possibly, they could be considered as "quasiparticles" - quanta of energy, but equating their relationship to sound waves with the photon/light relationship seems a step too far.
Not really Bill. If you think of how we define photons, they seem no less unreal than phonons. They don't 'exist', until a change.
The main difference I was thinking of was that light can be considered as waves or photons; but how reasonable would it be to say that sound could be considered as waves or phonons?
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If it is the phonons in a lattice that slow the passage of light through a medium, and phonons are a feature of sound waves, can sound slow light?
One complication might be that sound has to travel through a medium, so it might be difficult to distinguish between the influence of the sound and the medium.
Perhaps this could be overcome by measuring the speed of light through the medium with and without the sound?
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A disturbance propagating through a field, AKA a particle, cannot escape the event horizon as it is free to move and cannot attain the escape velocity. A field through which a particle propagates does not move independently of its source. Therefore it does not need to escape anything. It possesses energy derived from its potential. The fossil gravitational field will not propagate gravitons out of an event horizon. However, gravity does not require gravitons to operate on objects.
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I'm not sure how far one can take it Bill. But it's still worth some pondering :)
Phonon's needs solids sort of, to exist. air, 'matter' a medium.
Photon's?
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https://nasa.tumblr.com/post/180400886404/gobble-up-these-black-hole-friday-deals
Not had time to look at this yet, but thought it might fit in a black hole thread, or provide some ideas for Xmas decorations.
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. A field through which a particle propagates does not move independently of its source.
Some time ago, you said of a field:
It also persists and has no apparent source other than itself.
Which leaves me wondering: does a field have a source, and if so, what would it be?
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Consider an electron. It is said to have its own field, the electron field. It propagates through this field. Does this field actually exist? The energy is not in this proposed field it is in the electron. Also, we cannot define a force we can associate with this supposed electron field. This is different to the electromagnetic or gravitational fields. These do have a source within the particles that generate them. Not all proposed fields are equal.
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An electron can propagate through the gravitational field of another object. Like an electron moving through the earth's gravitational field. The earth's field is generated separately from the electron. From an earth based frame the electron is moving and the earth is still. Therefore we can consider the earth's gravitational field to be still. All things are relative.
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If it is the phonons in a lattice that slow the passage of light through a medium, and phonons are a feature of sound waves, can sound slow light?
Although light and phonons can interact there is no evidence that phonons are the mechanism for light slowing in a medium.
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Although light and phonons can interact there is no evidence that phonons are the mechanism for light slowing in a medium.
If I remember rightly, the Aharonov–Bohm effect is involved in the interaction (that’s a bit above my “pay grade”). The question still remains: is such a reaction possible is zero time? If so, how? If not, wouldn’t the reaction slow the photon?
Unfortunately, I can’t find the source of the information about phonons slowing the passage of light through a lattice. It may have been in a book – back in the days when I had time to read.
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These do have a source within the particles that generate them.
Therein lies my problem.
If a particle is a disturbance in a field, how can a particle exist without a field?
If a field has to exist before it can be disturbed; how can the disturbance be the source of the field?
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If I remember rightly, the Aharonov–Bohm effect is involved in the interaction
I thought Aharonov–Bohm was to do with the potential vs field debate. Haven’t come across it with reference to slowing of light, but it has been observed in photon-phonon reactions.
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These do have a source within the particles that generate them.
Therein lies my problem.
If a particle is a disturbance in a field, how can a particle exist without a field?
If a field has to exist before it can be disturbed; how can the disturbance be the source of the field?
A field is a series of measurements made in space - most have a zero value in the quiescent state. Along comes an electron carrying a charge, value of electron field is disturbed and increases to that of the electron charge; electron passes by, disturbance goes, value of field drops to zero.
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These do have a source within the particles that generate them.
Therein lies my problem.
If a particle is a disturbance in a field, how can a particle exist without a field?
If a field has to exist before it can be disturbed; how can the disturbance be the source of the field?
A field is a series of measurements made in space - most have a zero value in the quiescent state. Along comes an electron carrying a charge, value of electron field is disturbed and increases to that of the electron charge; electron passes by, disturbance goes, value of field drops to zero.
Is the mistake to imagine the field as a "thing" rather than a series of measurements?
Am I into "interpretation territory"?
Or is the "measurement" definition the sine qua non of any subsequent (deeper?) understanding?
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Is the mistake to imagine the field as a "thing" rather than a series of measurements?
No. The reason is that it is a thing ie a series of values in an area of space. It can be considered as an object which can be discussed, manipulated mathematically etc.
However, I suspect you are asking whether it has a life of its own. Well, take a gravitational field, would it exist if there were no mass in the universe? It would certainly have zero magnitude. Despite that, we can still consider the concept of a gravitational field even if there is no mass.
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Is the mistake to imagine the field as a "thing" rather than a series of measurements?
No. The reason is that it is a thing ie a series of values in an area of space. It can be considered as an object which can be discussed, manipulated mathematically etc.
However, I suspect you are asking whether it has a life of its own. Well, take a gravitational field, would it exist if there were no mass in the universe? It would certainly have zero magnitude. Despite that, we can still consider the concept of a gravitational field even if there is no mass.
Can I apply a similar logic to any body (my own as an example)?
Is it/can it be defined as also a "series of values" , without inferring that it is insubstantial on that account?
So the various fields can be treated as bodies in the same way as any everyday object except that they are particular (and extremely fundamental) kinds of bodies.....
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I probably need to take this one (small) step at a time.
A field is a series of measurements made in space
What is being measured?
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I probably need to take this one (small) step at a time.
A field is a series of measurements made in space
What is being measured?
Depends on the field.
Simple examples:
Temperature field in a room is a scalar field measured at different points in the room.
Wind field at any point in the space around you is a vector field showing the speed and direction of the wind.
Gravitational field is also a vector field but measures the force on a test particle.
So with an electromagnetic field you are measuring the strength of the electric and magnetic fields.
Electron field is a bit more complicated as you have to measure charge, mass, spin, so it is much easier to talk about an electron field and treat it as an object rather than say “value of charge, mass, spin, etc at this point in spacetime” everytime.
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How do you measure a field when its value is zero?
How do you know there is a field there to measure?
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It all depends on the arrow,
We define it as future, present, and past
Practically present doesn't exist
Future and past does though
But what is a arrow?
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Another funny point is that the further you go into the past, the more fuzzy it becomes. The same goes for a future.
So, where are you
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How do you measure a field when its value is zero?
Same way you measured it when it wasn’t zero. If your anemometer isn’t turning then wind speed is zero.
How do you know there is a field there to measure?
Because you get a measurement >0 when the value isn’t 0 :)
Seriously, you have to have measured/detected something sometime otherwise you won’t know it’s there. Of course you might think it’s there because theory suggests it is, but until you actually measure it, or and effect of it, you will never know it exists.