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Old 04-13-2016, 11:55 PM
am77494 am77494 is online now
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Hawking radiation is new space time ?

If I understand correctly, some black holes "evaporate" over time by releasing Hawking radiation back to the universe.

Also if I understand correctly, the background radiation is the same everywhere in the universe since all the universe has the same age.

I am not sure if Hawking's radiation counts as new space time. But if there was some way to measure the background radiation for the mass/energy created by the Hawking radiation, will it be the same as the universe's background radiation ?
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Old 04-14-2016, 12:00 AM
bomberswarm2 bomberswarm2 is offline
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Stephen Hawking emits radiation?
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Old 04-14-2016, 12:37 AM
Trinopus Trinopus is offline
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I believe you are talking about two different effects.

Cosmic background radiation is universal, omnidirectional, and remarkably isotropic -- pretty much the same in all directions. It is conventionally described as the "last echoes of the big bang."

Hawking radiation happens across very high gravitational boundaries. Not only near black holes but it has also been observed near large atomic nuclei. ("The Breakdown of Empty Space" -- article in Scientific American some years ago.) Essentially, a particle/anti-particle pair pops into existence, and then pops out again -- this happens all the time, and is called "virtual particles." The effect is not observable. But sometimes, one of the pair is pulled into a gravitational well -- a black hole or a Uranium nucleus -- so that the other particle doesn't mutually annihilate with it, but wanders off, free, so that it appears to be "emitted" from the gravitational source.

I think these two different effects have nothing to do with each other.
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Old 04-14-2016, 12:54 AM
Colibri Colibri is offline
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Stephen Hawking emits radiation?
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Old 04-14-2016, 08:48 AM
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Cosmic background radiation is universal, omnidirectional, and remarkably isotropic -- pretty much the same in all directions.
Thank you for the reply Trinopus. My question is exactly on the universality of the cosmic radiation - is the cosmic background radiation present only in space-time created at the big-bang or is it also the same in new space -time created like Hawking radiation.
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Old 04-14-2016, 09:13 AM
Grey Grey is offline
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It's still a confusing question.

Are you asking "Is there a mechanism, similar to Hawking radiation, where spacetime can be created and not automatically cancelled out by recombining with it's anti-self?"

You see the problem with that statement? With virtual particles, you have pairs that when combined canceled out. Hawking radiation is simply what you get if one of the particles fails to recombined due to crossing an event horizon.

To extend that idea to spacetime, we would need a theory that allows for spacetime to exist in "pieces" and for these "pieces" to exist in 1 of 2 states and that on when recombined result in something, but nothing too strange. As far as I know we have no such theory and I while I've heard of theories where spacetime is granular the description was closer to tiles than particles.
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Old 04-14-2016, 09:39 AM
am77494 am77494 is online now
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Okay - I am not a physicist - so please bear with me. I will try to ask the question in a different way.

As I understand, the Big Bang is a singularity. It makes no sense to ask what the universe was like before the big bang. All of the universe (mass , space, time and all) have the timestamp of the start of the universe i.e. the background radiation.

As I also understand, a black hole is also a singularity. Although here it does makes sense (?) to ask what the black hole was before it became a black hole. So when the "matter" is recycled back from the black hole to the universe - does it retain the time stamp of the start of the universe (i.e. background radiation), or is the matter recycled back from the black hole have a time-stamp of its new creation date.
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Old 04-14-2016, 10:03 AM
Quercus Quercus is offline
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'Radiation' can mean different things. The Cosmic Background Radiation is basically (faint) microwave -length electromagnetic waves (like we're in a giant, very low powered microwave); it's just like light but a different wavelength.


Hawking radiation is not electromagnetic waves, but rather an irregular stream of particles flowing outward from the black hole.


So they're really not the same kind of thing at all.
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Old 04-14-2016, 10:06 AM
Grey Grey is offline
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I think you're confusing the cosmic background radiation with radiation dating techniques. Lets assume so and that way I can talk nonsense.

Current understanding is that the universe was incredibly energetic in its youth. As the universe expanded the energy density dropped and things started to happen. Fundamental forces differentiated, quarks and electrons start showing up and photons are bouncing around everywhere but are continually being re-absorbed so there's no free path for them to race off without being destroyed.

Spacetime expands further and thing cool down a little more an you wind up with quarks grouping together into protons which suddenly capture electrons and we have hydrogen. We also suddenly have a free path for photons to go racing off. This all takes place roughly 300,000 years after the initial expansion. The free photons are energetic and are from every part of spacetime. fast forward billions of years and when we look out into space we see some of these photons but they've been red shifted ("cooled" I guess would work) to the temperature we see today ~2.7K.

Back to hawking radiation. As you move to smaller and smaller regions of spacetime there's a seething bath of virtual particles. Since they immediately cancel out there's no net average change in the local energy density. However if the pair appear at an event horizon, one particle may slip over before it can recombine. The radiation doesn't originate from the black hole so it can't really tell you anything about it. The event horizon is just a place where this splitting can take place.
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Old 04-14-2016, 10:39 AM
Exapno Mapcase Exapno Mapcase is online now
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You're confused by the use of the word radiation in both contexts. It's analogous to dark matter and dark energy. People see the word dark in both and think there must be a connection. There isn't. Dark merely means unknown.

Hawking radiation is not at all like cosmic background radiation. For that matter, neither comes directly from a black hole. Hawing radiation is emitted at the event radius. The cosmic background radiation is the remnant of the entire universe at the time of inflation, which happened after the universe emerged from the singularity. And a singularity might not be a black hole. Singularity merely means not expressible in current physics.
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Old 04-14-2016, 11:02 AM
Francis Vaughan Francis Vaughan is offline
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As above - the word singularity doesn't define any sort of physical thing. Rather it does the opposite. It says - "here be dragons" or "all our rules break down here, we have no clue". The Big Bang started with a singularity - aka a point of "we have no clue". There are other things for which we have no clue as well. The middle of a black hole being one. But you can't really equate two different instances of "we have no clue".
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Old 04-14-2016, 12:32 PM
am77494 am77494 is online now
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I think you're confusing the cosmic background radiation with radiation dating techniques. Lets assume so and that way I can talk nonsense.
Grey - I think I know the difference between cosmic background radiation and radiation dating techniques.

I am using Hawking radiation as an example of the energy/matter recycled back from a singularity (black hole) to the universe. If it makes more sense to you - then consider matter recycled back from a black hole http://www.rawstory.com/2013/11/new-...ck-into-space/

So if one were to measure the back ground radiation around this matter - will it show the signature of the big bang or the signature of the black hole ?

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Originally Posted by Francis Vaugha
There are other things for which we have no clue as well. The middle of a black hole being one.
We do have one BIG clue for the middle of the black hole - that the matter in it came from the Big Bang. The question is - when a black hole like this "evaporates" back into the universe, does the recycled matter appears as it was created at the big bang ? or does it have a different background signature ?

Last edited by am77494; 04-14-2016 at 12:33 PM.
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Old 04-14-2016, 12:46 PM
Exapno Mapcase Exapno Mapcase is online now
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The question is - when a black hole like this "evaporates" back into the universe, does the recycled matter appears as it was created at the big bang ?
No, absolutely not.

Nor is the matter inside the black hole recycled and create a signature. Energy is subtracted from the black hole by the separation of pairs of identical virtual particles. This tells us nothing about what is inside the black hole. It is a different process leading to a different outcome. They have no similarity except that they happen to use the word radiation.
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Old 04-14-2016, 12:49 PM
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No, absolutely not. .
So if one were to measure the background radiation around this recycled matter - it wont be the same as the rest of the universe ? Am I understanding you correctly ?
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Old 04-14-2016, 01:01 PM
Francis Vaughan Francis Vaughan is offline
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The CMBR is the remnant of the Big Bang - it is a remnant because of the expansion of the universe. It will continue to become further red-shifted as the universe ages further. It is a black body radiation (indeed it is the most perfect black body we know of, fitting the theoretical spectrum to silly accuracy.)

An evaporating black-hole doesn't have background radiation (other than the CMBR) but it does itself radiate. I have no idea if the spectra of Hawking radiation is a black body. I would guess it might be. But even if it is, the temperature it represents has no relationship to the CMBR. There is common physics, but that is all.

The question of recovering information out of an evaporating black hole about what went in, is one of the more interesting outstanding questions.

Last edited by Francis Vaughan; 04-14-2016 at 01:03 PM.
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Old 04-14-2016, 02:04 PM
Francis Vaughan Francis Vaughan is offline
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To add. Indeed Hawking radiation is exactly black body. Not surprised.

So, the difference is that the CMBR is the remnant of the early hot universe at the point it had cooled to become transparent. It isn't a remnant of the Big Bang directly, it is quite a bit later. The universe expands and this all pervading radiation gets stretched out so much that it is red-shifted right down to microwaves, and the equivalent black body is seriously cold. That is all it is. It isn't in any way a special signature of the Big Bang.

Hawking radiation has a spectrum that is related directly to the mass of the black hole.

They are both black bodies. End of story.

There does remain the question of conservation of information. Quantum theory doesn't like information to be destroyed. But an evaporating black hole doesn't transmit information from within itself, even as it becomes diminished to nothingness. This is a source of problems. There are some suggestions, but I'm not sure anyone is satisfied with the current state of understanding.
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Old 04-14-2016, 02:30 PM
Exapno Mapcase Exapno Mapcase is online now
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So if one were to measure the background radiation around this recycled matter - it wont be the same as the rest of the universe ? Am I understanding you correctly ?
There is no background radiation. There is no recycled matter. Your understanding of Hawking radiation is completely wrong. You have a garbled mental picture of what is happening. Please read what the physicists here are trying to explain to you.
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Old 04-14-2016, 03:49 PM
Chronos Chronos is offline
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The cosmic microwave background is not an inherent feature of the fabric of space, or anything like that. If you build a sealed box surrounded by wire mesh with a spacing of less than a millimeter or so, then that box will contain no CMB radiation. If you open it up and expose it to the sky, then microwaves will enter it. Any given microwave photon will only be in the box for a very short time before hitting the back wall, but as long as the box remains open and exposed, it'll be replaced by other photons coming in. Close the box, and new photons stop coming in, and the photons that were in the box at the time all hit the back of the box.
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Old 04-14-2016, 03:50 PM
Grey Grey is offline
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Grey - I think I know the difference between cosmic background radiation and radiation dating techniques.
Honestly, you don't seem to.

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I am using Hawking radiation as an example of the energy/matter recycled back from a singularity (black hole) to the universe. If it makes more sense to you - then consider matter recycled back from a black hole http://www.rawstory.com/2013/11/new-...ck-into-space/

So if one were to measure the back ground radiation around this matter - will it show the signature of the big bang or the signature of the black hole ?
You misunderstand the linked story. The article is pointing out that galactic black holes are engines for moving matter about galaxies. They rip apart material in their accretion disks which then get caught up in their intense tangle of fields which throws some of those materials out of the galactic core.

It says nothing about materials which pass the event horizon being recycled.
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We do have one BIG clue for the middle of the black hole - that the matter in it came from the Big Bang. The question is - when a black hole like this "evaporates" back into the universe, does the recycled matter appears as it was created at the big bang ? or does it have a different background signature ?
Look, Hawking radiation, at the event horizon effectively has a particle escaping into space and the other passing into the blackhole. That's it. The particles do not come from the black hole.

Last edited by Grey; 04-14-2016 at 03:51 PM.
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Old 04-14-2016, 04:24 PM
Blue Blistering Barnacle Blue Blistering Barnacle is offline
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Grey - I think I know the difference between cosmic background radiation and radiation dating techniques.

I am using Hawking radiation as an example of the energy/matter recycled back from a singularity (black hole) to the universe. If it makes more sense to you - then consider matter recycled back from a black hole http://www.rawstory.com/2013/11/new-...ck-into-space/

So if one were to measure the back ground radiation around this matter - will it show the signature of the big bang or the signature of the black hole ?



We do have one BIG clue for the middle of the black hole - that the matter in it came from the Big Bang. The question is - when a black hole like this "evaporates" back into the universe, does the recycled matter appears as it was created at the big bang ? or does it have a different background signature ?
If I understand him correctly, Susskind had a long-running disagreement with Hawking about black holes and entropy. I am poorly equipped to discuss this, so please take this with a grain of salt.

Hawking felt that stuff fell into a black hole and was essentially lost forever. While a black hole could evaporate, the Hawking Radiation had no strict relation to that which had fallen in.

Susskind felt that this created information loss unacceptable to quantum theory.

This debate was ultimately resolved in Susskind's favor, and Hawking published a paper proving Susskind correct.

I think that somehow the information of stuff that fell in is encoded in the Hawking radiation. I don't much understand it. Hopefully someone will explain this shortly.

I don't know that it would be possible, even for Brainiac, to decipher Hawking radiation to learn anything meaningful about stuff that fell in. Even if you could do that, except for the possible but unconfirmed existence of quantum black holes created in the Big Bang, black holes are born of dying stars and arrived on the scene long after the Big Bang.
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Old 04-14-2016, 04:27 PM
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The black hole information paradox is indeed a topic of much dispute. And one possible resolution is in fact that the information is somehow encoded in the Hawking radiation. But there has been no model proposed that describes how this could happen, or in what form the information would be encoded, or anything else of the sort. As of right now, it's little more than a handwavy guess.
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Old 04-14-2016, 04:54 PM
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So if one were to measure the background radiation around this recycled matter - it wont be the same as the rest of the universe ? Am I understanding you correctly ?
See this? This is why I think you're conflating CMB with radioactive decay. The CMB are photons from the early years of the universe. That's it.

The particles involved in Hawking radiation do not emit CMB photons. They are the radiation.
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Old 04-14-2016, 04:59 PM
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So if one were to measure the background radiation around this recycled matter - it wont be the same as the rest of the universe ? Am I understanding you correctly ?
Background radiation is not a property of matter. This is your big hangup. It is a property of the universe. Neither the matter that entered the black hole, nor the matter that is evaporated have "background radiation", though it may radiate on its own. It's like you're asking about the color of a song, and whether it has the same color before and after you sing it.
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Old 04-14-2016, 05:37 PM
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Or to put it another way, suppose you put a detector next to a lump of uranium. You detect radiation coming from the uranium. You can measure how much radiation the lump of uranium produces. You can do this for all sorts of things. Hot light bulbs. Radio transmitters. Lumps of ice. Rocks. All these things absorb and produce radiation.

It turns out that when you measure the radiation put out by all the things next to you...the rocks, light bulbs, lizards, radio stations, stars, lumps of uranium, and one by one eliminate them, you still find radiation. And this radiation is coming from every point in the universe in exactly the same amount. If you look at a star, the radiation gets more intense as you get closer. But not this leftover radiation.

Of course the background radiation can be blocked by all sorts of things, like the earth. So if you're on Earth you can only detect the background radiation from the sky.

But the background radiation is just one of lots of other sources of radiation. So if you were near a black hole and could detect the Hawking radiation from it, you could also detect the background radiation. Just like if you were in a room with a hot light bulb and a radio transmitter you could detect both the light and the radio waves. The background radiation is just very very very very very very low energy radio waves. Or maybe they shouldn't be called radio waves but something else. But they are are sort of like radio waves.
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Old 04-14-2016, 08:26 PM
Trinopus Trinopus is offline
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The cosmic microwave background is not an inherent feature of the fabric of space, or anything like that. If you build a sealed box surrounded by wire mesh with a spacing of less than a millimeter or so, then that box will contain no CMB radiation. . . .
??? Certain of this? I would have said, yes, the CMB is an innate property of our cosmos's space-time, and, if you could isolate a smallish chunk of the cosmos, it would be active with this radiation. Maybe not in a millimeter box, but in a light-year box.

(The CMB is brightest at around 2mm, so it would be darn tricky to observe it inside a 1mm box.)

(It's still very different from the emission of particles near a black hole, so, to answer the OP, no, Hawking radiation will not resemble Cosmic Background Radiation. The former is usually individual particles, and the latter is a smooth, low-frequency EM radiation.)
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Old 04-14-2016, 08:31 PM
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Hawking radiation and the CMBR both have a black body spectra, but the CMBR is isotropic and homogeneous and Hawking radiation is not. This if you like is a product that the CMBR is radiation emitted at some stage in an isotropic and homogeneous spacetime, whereas Hawking radiation is a semiclassical property of a BH spacetime which at best will only have radial symmetry.

However the key ingredient needed for Hawking radiation is an event horizon (or I believe an apparent horizon will suffice) and our Universe, for each spatial location, has a cosmological event horizon. The difference is that a BH event horizon is the boundary of what can reach future null infinity, whereas a cosmological event horizon is the boundary of what can reach a certain spatial location. It is believed that there is radiation associated with our cosmological event horizon in a way that is analogous to the Hawking effect for a BH event horizon, but the difference between the two horizons (as stated in the previous sentence) makes the physicality of such radiation shakey.

Regardless though this "cosmic Hawking-Gibbons radiation" would have a wavelength much, much larger than the wavelength of the CMBR and so the two are not the same.
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Old 04-14-2016, 08:41 PM
Chronos Chronos is offline
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Not a one-millimeter box. A big box (however big you like), made of mesh with a one-millimeter spacing. And no, you wouldn't observe any CMB radiation in that box: Where would it be coming from?
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Old 04-14-2016, 08:59 PM
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Not a one-millimeter box. A big box (however big you like), made of mesh with a one-millimeter spacing. And no, you wouldn't observe any CMB radiation in that box: Where would it be coming from?
Unless the mesh temperature is below about 2.7K won't it be emitting CMB ?
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Old 04-14-2016, 09:03 PM
Chronos Chronos is offline
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No, it would be emitting its own thermal radiation, which would bear no particular relationship to the CMB.
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Old 04-14-2016, 09:21 PM
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No, it would be emitting its own thermal radiation, which would bear no particular relationship to the CMB.
Just so I understand what you are saying : if I take your mesh box and have a very high resolution device inside that produces a spectrum - the spectrum will have only one peak corresponding to the temperature of the mesh and the spectrum peak corresponding to the CMBR will be missing ?
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Old 04-14-2016, 09:25 PM
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Unless the mesh temperature is below about 2.7K won't it be emitting CMB ?
Are there any photons from the birth of the universe inside it?
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Old 04-14-2016, 09:31 PM
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Are there any photons from the birth of the universe inside it?
Grey - I think you meant to ask Chronos that question. As far as I understand, you will always have photons from the birth of the universe everywhere.
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Old 04-14-2016, 09:45 PM
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Look, Hawking radiation, at the event horizon effectively has a particle escaping into space and the other passing into the blackhole. That's it. The particles do not come from the black hole.
Grey - thank you for bearing with me. So say a small region of the universe is made up of such escaped particles - can we call that part younger than the big bang ? If I did the spectral analysis in this region with an extremely sensitive instrument, will I see the peak (line) corresponding to the CMBR ?
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Old 04-14-2016, 09:53 PM
Francis Vaughan Francis Vaughan is offline
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If you build a nice big box instantaneously, it will contain CMBR for as long as it takes those photons to hit the walls of the box. Then there will be no more. The box will be empty of them. If you built your box from material at say 0.1K, there would be a background radiation with a spectrum corresponding to that temperature.

The CMBR is no different to the starlight we observe from very distant galaxies, it is just that it comes from a time in the universe's history before even galaxies existed. So early that there was just pure very very hot matter. All we are seeing is the red-shifted image of that matter.

There is a gap in our ability to observe things between the CMBR and very old galaxies, but this is technological. The interest in infra red astronomy seeks to push our ability to see ancient galaxies back further. The Web Space Telescope is especially directed at this gap.

The point being that the CMBR is no more a signature of the Big Bang than anything else you see. It turns out that with some effort we can observe some interesting things about it, and those observations allow us to validate some theories and refute others about the nature of the universe's origins. But there is nothing intrinsicly special here except that the CMBR is the oldest thing we can observe.

Last edited by Francis Vaughan; 04-14-2016 at 09:55 PM.
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Old 04-14-2016, 09:59 PM
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Grey - I think you meant to ask Chronos that question. As far as I understand, your will always have photons from the birth of the universe everywhere.
No it was to you.
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Old 04-14-2016, 10:15 PM
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If you build a nice big box instantaneously, it will contain CMBR for as long as it takes those photons to hit the walls of the box. Then there will be no more. The box will be empty of them. . . .
Cool! (Jape intended...) I had thought the CMB was a property of space-time, and would be continued to be generated by empty space. I thought that it was due to the "temperature" of empty space. Empty space is about 3 degrees Kelvin, and thus radiates blackbody mw.

I'm being told no...but this is hard to swallow, as it contradicts what I've read so many places...
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Old 04-14-2016, 10:18 PM
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Grey - thank you for bearing with me. So say a small region of the universe is made up of such escaped particles - can we call that part younger than the big bang ? If I did the spectral analysis in this region with an extremely sensitive instrument, will I see the peak (line) corresponding to the CMBR ?
CMB photons are not emitted by space, they're photons emitted just as the early universe became transparent. They raced off and have never bumped into anything since... Well except for whatever detects them.

Let's take Chronos's box and wait a few minutes to let any CMB photons in the box when it appeared to be absorbed or escape. So now you would never detect a CMB photon in the space but the place would be filled with virtual particle pairs appearing and disappearing. These are the particles that, when one is lost across an event horizon, make up Hawking radiation.
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Old 04-14-2016, 10:20 PM
Trinopus Trinopus is offline
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Grey - thank you for bearing with me. So say a small region of the universe is made up of such escaped particles - can we call that part younger than the big bang ? If I did the spectral analysis in this region with an extremely sensitive instrument, will I see the peak (line) corresponding to the CMBR ?
As I understand it (and this appears to be evolving!) yes, and yes. The particles emitted from a black hole (or near a massive atomic nucleus) would have a completely different spectrum than the cosmic background, but the cosmic background would still be observed in the same region as emitted Hawking radiation.

Sort of like... It's daylight, and sunlight is everywhere -- it's on your roof, and your garden, and your car. Meanwhile, you have a microscopic black hole in your hand. It's emitting radiation...but that radiation has no relationship to the sun's heat-and-light radiation, which is all around you, including on your hand. Your hand has the unique benefit of both kinds of radiation.

ETA: I don't like the phrasing "a region of the universe is made of such particles." No: they're within space-time. They do not "make up" new space-time. I think this may be a basic problem with how things are getting phrased here.

Last edited by Trinopus; 04-14-2016 at 10:22 PM.
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Old 04-14-2016, 11:23 PM
Exapno Mapcase Exapno Mapcase is online now
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Originally Posted by am77494 View Post
can we call that part younger than the big bang ?
No. That portion of space-time is exactly as old as every other portion of space-time.

The individual particles are new, in the sense that particles often appear. The photons by which you are reading this are new and have just now appeared. Particles are not space-time. Radiation is not space-time. (Are particles=radiation? Unh-uh. Not touching that one. Go read a QM textbook.) You appear to want the two to be the same, but it's not going to happen.
  #40  
Old 04-14-2016, 11:53 PM
Francis Vaughan Francis Vaughan is offline
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The confusion may come about from a simple mistake in tense. The CMBR does not come from everywhere. It came from everywhere. It stopped being created 14 billion years ago. But at that moment very part of the universe was emitting those photons. Right now you are made of particles that were once part of that super hot soup that created the CMBR. But a lot has happened in the universe since then.
  #41  
Old 04-15-2016, 09:44 AM
scr4 scr4 is online now
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The OP seems to think the cosmic microwave background radiation (CMBR) was generated by the Big Bang singularity. This is incorrect. The CMBR was emitted by ordinary matter (plasma) that filled the universe (normal space as we know it) when the universe was young. Eventually the universe expanded and cooled to a point where the opaque soup of plasma turned into a clear space filled with hydrogen atoms. The radiation from the plasma has been flying around ever since, getting diluted by the expansion of space.

Last edited by scr4; 04-15-2016 at 09:44 AM.
  #42  
Old 04-15-2016, 02:16 PM
naita naita is offline
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Quote:
Originally Posted by Trinopus View Post
Cool! (Jape intended...) I had thought the CMB was a property of space-time, and would be continued to be generated by empty space. I thought that it was due to the "temperature" of empty space. Empty space is about 3 degrees Kelvin, and thus radiates blackbody mw.

I'm being told no...but this is hard to swallow, as it contradicts what I've read so many places...
You had that backwards. The temperature of empty space is described as being 3 K because that's the black body temperature the heavily red-shifted CMBR corresponds to. (And it's an apt description, since that's then the equilibrium temperature of an object in empty space.)
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