Ask a physicist

[llafnwod]

I would question the non of the fallout thing since yes while their is no radioactive waste left over annihalation turns the mass of the objects completly into gamma radiation at an extreem rate (E=mc[sup]2[/sup] and all). So the shear amount of radiation will be beyond current comprehension and that is bound to cause havoc with elecments in rocks and trees etc and make them radioactive leading to indirect fallout answell as a highly irradiated area.

Not really. I was talking about a bomb within an order of magnitude or two of the power of a current fusion warhead. The sorts of processes you're describing take place in high-energy laboratories, extremely high mass stars, and supernovae. Yes, there will be a huge burst of gamma radiation at the moment of the explosion, but that's not really fallout and a bomb of that magnitude is not going to cause much past temporary ionization.

 

[WarriorFH]

If black holes are so dense that nothing can escape them, then why do they emit radiation?

 

[llafnwod]

If black holes are so dense that nothing can escape them, then why do they emit radiation?

It's really, really complicated. Look up Hawking radiation. Put simply, it's not actually the black hole emitting a particle. Wikipedia does a decent job of simplifying it:

A slightly more precise, but still much simplified, view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes. In order to preserve total energy, the particle that fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole). By this process, the black hole loses mass, and, to an outside observer, it would appear that the black hole has just emitted a particle.

 

[TheScientificIssole]

Where'd I leave my YoYo?
Also how exactly does one blind someone with science?

 

[MikailCaboose]

Which idea of universe 'creation' i.e how it started, do you favor?
And isn't the big bang theory just on how it expanded 'n stuff after creation, not creation itself?

...

I haven't done advanced physics.

Well their isn't really many theories of creation if we discount the big bang theory as one and say it's just expansion, getting into the relms of where theists bring out the "G word".

I do favour the big bang theory though there are a few holes here and there. The universe would have had to undergo very fast expansion indeed to look the way it does today however mass fluctuations were needed to produce anythinjg we see since a universe of constant density everywhere would never end up with structure since everything would have experienced equal force in every direction and inflation periods would be problamatic to this. Plus since Steven Hawking himself now disagrees with the big bang theory (even though it's his theory) so who am I to argue?

So what do you think of the possibility of a multiverse, with our universe being the result of a collision between multiple universes? (note that astrophysics, and physics in general is just a hobby of mine, and I don't really pay a hole lot of attention to it.)

 

[cookyy2k]

Snippedy

Well I hope that helped, it's certainly an interesting field and I've done quite a bit of quantum mechanics thought this is not exhaustive and I'm no expert.

Thank you so much. It's certainly done more than helped. As I said, when I read the original article, I was a little suspicious, simply because the idea seemed so 'out there', psychedelic, and illogical that I doubted it had much acceptance amongst the 'real' scientists who seem to value 'logic' as the be all and end all. You've not just explained it to me, but shown that it's an actual hypothesis with real study behind it. Having such a trippy idea confirmed as a real scientific hypothesis has only confirmed to me that the Universe we live in is a magical (descriptively, not literally) construction that operates on principles so vast and mind-bending we can barely even comprehend them (though that doesn't mean we shouldn't try).

You may have guessed that I have a fondness for some of the... more colourful explanations of how and why we're here. I'm certainly no luddite (without advancements in birthing technologies, I likely wouldn't have survived being born), but I despair at how people who proclaim science as the answer and people who proclaim spirituality as the answer often fail to see the common ground in-between. I hope it doesn't sound like I'm putting words in your mouth, but for me this theory (along with others) shows that there are aspects of our existence which we cannot even begin to fathom yet.

As a quick addition to my orginal question: I remember this article briefly going off on the tangent that quantum entanglement may mean there is at least a little scientific truth to such esoteric ideas as the "one-consciousness" concept, or ideas of animism. Would it be correct, therefore, that the idea of quantum entanglement could hypothetically be used to re-evaluate ideas that previosusly were dismissed for having little scientic grounding. To use one example I brought up: the one consciousness idea. If particles can have an effect on each other after being scrambled, does that mean it's theoretically possible for human minds (specifically brains, I suppose, because after all, it is the brain which is made up of particles) to affect each other despite the lack of a physical connection? The article I read (it was in the London Metro, by the by) suggested that because all particles were bunched together at the start of the universe, theoretically all the particles that make up every human brain were scrambled together at the point of singularity.

It's quite a weird sounding idea, I know, and you may simply think it's nothing more than takign a perfectly good idea and using it to support crackpot new-age nonsense.

Also, light. Is it particle or wave? And is it true that actually observing experiments on the subject has profoundly affected the results?

It does seem to be one of those cases of stretching the theory a little too much. A human brain works on electrical impulses, this is not something that can be entangeld. I our brains used spintronic impulses (using the spin of the elctron not the charge to transfere information) then I could see the logic to it. I could see how electrons and other particles could be entangled between different brains however I can't see how that would mean one person could effect the other. Our bodies don't care what spin an electron has, if it did an MRI would probably be fatal.

Light is both at once, it's a hard concept but in quantum mechanics it's a property called wave-particle duality. electrons and protons are also both at the same time.

The observation changing the result thing is one of the problems with Quantum mechanics. For example any particle (lets use the electron again) can be thought of as a wave, this wave is called the wave function, the probability of finding the electron in a certain point in space is equal to the wavefunction at that point squared. From the wave function properties such as momentum can be calculated. However this method requires the wave function to be smootly varying in time, that is it never "jumps" around from time to time. So if you measure the exact possition of the electron the wave function will jump to it having zero probability everywhere other than where it is, and 1 at it's possition. The wave function has just "jumped" they call this the wavefunction collapse. Now you know the position however in doing so you've collapsed the wavefunction and so the momentum you measured earlier using that wavefunction is now wrong, you cannot know it. If you let the electron go again and use it's wavefunction to find its momentum you've now lost it's possition information because it's a wave function probability again.

 

[llafnwod]

So what do you think of the possibility of a multiverse, with our universe being the result of a collision between multiple universes? (note that astrophysics, and physics in general is just a hobby of mine, and I don't really pay a hole lot of attention to it.)

Definition of UNIVERSE
1: the whole body of things and phenomena observed or postulated : cosmos

Even if there are "other" universes, the question remains as to where they came from.

 

[cookyy2k]

I would question the non of the fallout thing since yes while their is no radioactive waste left over annihalation turns the mass of the objects completly into gamma radiation at an extreem rate (E=mc[sup]2[/sup] and all). So the shear amount of radiation will be beyond current comprehension and that is bound to cause havoc with elecments in rocks and trees etc and make them radioactive leading to indirect fallout answell as a highly irradiated area.

Not really. I was talking about a bomb within an order of magnitude or two of the power of a current fusion warhead. The sorts of processes you're describing take place in high-energy laboratories, extremely high mass stars, and supernovae. Yes, there will be a huge burst of gamma radiation at the moment of the explosion, but that's not really fallout and a bomb of that magnitude is not going to cause much past temporary ionization.

The 8g of anti-matter we do have, plus 8g of matter required for anhilation would produce 1.4x10[sup]15[/sup]J of radiation. That is quite a bit and for only 8g of anti-matter.

If black holes are so dense that nothing can escape them, then why do they emit radiation?

I covered this one earlyer in the thread too, along with a link to Hawking's origional paper.

Where'd I leave my YoYo?
Also how exactly does one blind someone with science?

Don't know about the yoyo, but a laser is a good blinding devise.

So what do you think of the possibility of a multiverse, with our universe being the result of a collision between multiple universes? (note that astrophysics, and physics in general is just a hobby of mine, and I don't really pay a hole lot of attention to it.)

It is certainly an interesting hypothesis, that I have only ever really read a little on. One of the theories for gravily is that it is so weak due to it leaking from another dimention in a multivesre. It's not impossible, but also it's not really testable even on a theoretical standing since all our laws of physics work in our known universe, we don't even know if our laws hold up for all our universe of just a special patch around us so going for outside our universe thoughts is a little beyond me.

 

[ShadowKatt]

Galactic dynamics and astrophysics, eh? Alright, I have a question for you.

There is generally one scientific theory on how the universe started, that being the big bang. There are several theories about what brought about the big bang, contact between universal branes(M-theory), phase transition(strange theory), or universal creator(the religous theory). Any one of these are...somewhat valid, and they all share the common big bang. The end of the universe is another matter.

There are several theories about the end of the universe, which I'm sure you're already familiar with. There's the Big Crunch, whereas the universe ceases its expansion and collapses in on itself before exploding forth once more. Observed universal expansion discounts this somewhat however the rate of deceleration may be so small that we can't measure it at this point. Then there's the Big Freeze, which I subscribe to, where the universe continues to expand outwardly forever until entropy reduces the entire universe into an energeticly void expanse. Then there's the Big Rip.

This one is rather new to my experience, and of all the theories I've heard, it's hard not to call this one out as batshit insane=slash-stupid. The theory is that as the universe expands, it will come to a breaking point, like an elastic band, pulling and pulling and pulling until eventually it tears. At that moment, every particle in the universe will be ripped down to its smallest sub-atomic particles at the same time. Planets and stars will be vaporised, nebulae will disperse, and the entire universe will essentially end up identical to the Big Freeze, only a hell of a lot faster and more sudden and with nothing larger than the smallest possible particle existing.

I would like to know what physics support this theory and if such a thing would even be viable in the first place. What possible attractive universal forces would actually increase with increasing distance and cause a ripple effect that would destroy all matter? Or, have you not even heard of this theory before?

 

[MikailCaboose]

So what do you think of the possibility of a multiverse, with our universe being the result of a collision between multiple universes? (note that astrophysics, and physics in general is just a hobby of mine, and I don't really pay a hole lot of attention to it.)

It is certainly an interesting hypothesis, that I have only ever really read a little on. One of the theories for gravily is that it is so weak due to it leaking from another dimention in a multivesre. It's not impossible, but also it's not really testable even on a theoretical standing since all our laws of physics work in our known universe, we don't even know if our laws hold up for all our universe of just a special patch around us so going for outside our universe thoughts is a little beyond me.

And now for one more question, and I don't know if you have answered this in some way, oops.
But, what do you think about brane theory?

 

[cookyy2k]

Galactic dynamics and astrophysics, eh? Alright, I have a question for you.

There is generally one scientific theory on how the universe started, that being the big bang. There are several theories about what brought about the big bang, contact between universal branes(M-theory), phase transition(strange theory), or universal creator(the religous theory). Any one of these are...somewhat valid, and they all share the common big bang. The end of the universe is another matter.

There are several theories about the end of the universe, which I'm sure you're already familiar with. There's the Big Crunch, whereas the universe ceases its expansion and collapses in on itself before exploding forth once more. Observed universal expansion discounts this somewhat however the rate of deceleration may be so small that we can't measure it at this point. Then there's the Big Freeze, which I subscribe to, where the universe continues to expand outwardly forever until entropy reduces the entire universe into an energeticly void expanse. Then there's the Big Rip.

This one is rather new to my experience, and of all the theories I've heard, it's hard not to call this one out as batshit insane=slash-stupid. The theory is that as the universe expands, it will come to a breaking point, like an elastic band, pulling and pulling and pulling until eventually it tears. At that moment, every particle in the universe will be ripped down to its smallest sub-atomic particles at the same time. Planets and stars will be vaporised, nebulae will disperse, and the entire universe will essentially end up identical to the Big Freeze, only a hell of a lot faster and more sudden and with nothing larger than the smallest possible particle existing.

I would like to know what physics support this theory and if such a thing would even be viable in the first place. What possible attractive universal forces would actually increase with increasing distance and cause a ripple effect that would destroy all matter? Or, have you not even heard of this theory before?

I've not heard this one before however I can see from your setting it out one major factor that could support this. As space expands so do the gaps between nucleons, nuclii/electrons and so on. eventually their could come a time when the nuclear restoring force in the nucleus or the bonds between molecules are just too long to be held together and then it all falls apart.

I favor the big freeze also, the universe at current is expanding just enough not to collapse back together and should keep going that way. It's the lack of knowlage about dark matter, which is my field, that is stopping us from saying with certanty which is going to happen.

And now for one more question, and I don't know if you have answered this in some way, oops.
But, what do you think about brane theory?

I have answered this in some way actually in that I've said I just don't know enought about string theory to makje sense of the papers or research material and don't really have the time to learn the entire field since it wasn't covered in my UG days and I ahven't touched it in PG either.

 

[LordOrin]

Cool thread.

Why are scientists sure of the existence of dark matter, as opposed to there being something wrong with the way we're measuring the mass of galaxies?

And how do we know the extra mass isn't coming from black holes that we haven't detected?

 

[FoolKiller]

Why is Pluto no longer a planet?

 

[cookyy2k]

Cool thread.

Why are scientists sure of the existence of dark matter, as opposed to there being something wrong with the way we're measuring the mass of galaxies?

And how do we know the extra mass isn't coming from black holes that we haven't detected?

My research field again.

We arn't 100% sure of dark matter but it's certainly not miss measurement of galaxy masses since the luminous matter in the Galaxy just doesn't have the right shape, densit or size to produce what we're seeing. It can be put down to stuff we can't see/measure being theie but that's dark matter.

Black holes along with gravity acting differently on larger scales are the two contendors against DM. Now the things I always say are a little biased since all my work assumes DM but here goes. The cold dark matter model we use today in galactic dynamics makes several predictions that have all been observed to be true since the predictions were made so it's not just fitting the numbers to the observation. the way in which galaxies form in CDM leaves a lot of dark matter fragments in the Galaxy (in the Milkyway 100-1000 fragments of a few thousand to tens of millions of solar masses) these act to asymmertarise the galactic gravitational potential and this has been observed to be true. these clumps may be undiscovered black holes but around 4 of these clumps have been see with stars in very close proximity to where they are predicted to be, a black hole massive enought to cause the potential would be destroying these stars so visible from it's acreation disc. Another is that these fragments are distortable due to the fact they're made of man constituant parts, this has been observed when clusters as old as the Galaxy suddently have a blip in their orbit, this is thought to be the DM fragment having ebing broken by a gravitational event and so effecting the cluster.

Now their are 2 major problems in CDM to be resolved. 1)we predict many more fragments than we've ever seen, though as discussed they're really hard to see. 2) the main halo should have infinate potential at r=0, this isn't the case obviously thought their is a super massive black hole at the centre so the potential is very high.

And finally. I really really hope DM theory is correct. My work relies on it but more importantly all the work in the field for the last 50 years relies on it. If it turns out to be wrong we're being put back 50 years and worse still funding bodies and research councils will be slow to trus us again after 50 years of wasted money if DM theory is wrong.

Why is Pluto no longer a planet?

Pluto unfortunately failed to meet the criteria that was decided upon to designate something a planet. When it was discovered their was no hard and fast rules as to what a planet was so they decided it's a planet.

The criteria are:

(a) in orbit around the Sun
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (is roughly spherical).
(c) has cleared the neighbourhood around its orbit.

Now as you can see the Earth meets all these, we orbit the sun, it is roughtly spherical and we have no major objects in our orbital path.

Pluto however came up against a few problems. It does orbit the sun, but it's orbit is verry erratic and not in the same plane as the rest of the panets. It doesn't meet b, it's egg shaped, it's mass is not sufficient to produce something roughly spherical. And it definately fails on c since it's in an asteroid belt.

Thus it was classified a dwarf planet. If we'd made the definition to allow pluto planet status we would have to add 4 other objects as planets and probably many more down the line.

 

[Hungry Donner]

Why is Pluto no longer a planet?

When Pluto was discovered it was unique, and because of this it became a planet. However recently we have discovered that there are a lot of similar objects out there. For the simple sake of consistency either these objects had to be considered planets too or Pluto had to be demoted.

This isn't the first time that scientists have dealt with this situation. When Ceres was first discovered it was considered a planet, but later it was discovered that there were other similar bodies. Now Ceres is recognized as the largest member of the asteroid belt, just as Pluto is recognized as a prominent member of the Trans-Neptunian Objects (or Plutoids).

If you look at the solar system as we know it today, with quite a large number of these TNOs flying about, Pluto no longer looks unique at all. However there are four prominent rocky planets in the interior of the system and four very prominent gas giants further out. Pluto isn't really on the radar.

 

[llafnwod]

I would question the non of the fallout thing since yes while their is no radioactive waste left over annihalation turns the mass of the objects completly into gamma radiation at an extreem rate (E=mc[sup]2[/sup] and all). So the shear amount of radiation will be beyond current comprehension and that is bound to cause havoc with elecments in rocks and trees etc and make them radioactive leading to indirect fallout answell as a highly irradiated area.

Not really. I was talking about a bomb within an order of magnitude or two of the power of a current fusion warhead. The sorts of processes you're describing take place in high-energy laboratories, extremely high mass stars, and supernovae. Yes, there will be a huge burst of gamma radiation at the moment of the explosion, but that's not really fallout and a bomb of that magnitude is not going to cause much past temporary ionization.

The 8g of anti-matter we do have, plus 8g of matter required for anhilation would produce 1.4x10[sup]15[/sup]J of radiation. That is quite a bit and for only 8g of anti-matter.

Yes, it is, but that's just a number. What I was saying was that an antimatter bomb roughly comparable to a current fusion bomb would not irradiate the surrounding area. An antimatter bomb capable of the transmutation of radioactive elements out of base metals and minerals would be less a bomb and more a world-ending cataclysm, in which case I don't think you have to worry too much about fallout.

 

[cookyy2k]

I would question the non of the fallout thing since yes while their is no radioactive waste left over annihalation turns the mass of the objects completly into gamma radiation at an extreem rate (E=mc[sup]2[/sup] and all). So the shear amount of radiation will be beyond current comprehension and that is bound to cause havoc with elecments in rocks and trees etc and make them radioactive leading to indirect fallout answell as a highly irradiated area.

Not really. I was talking about a bomb within an order of magnitude or two of the power of a current fusion warhead. The sorts of processes you're describing take place in high-energy laboratories, extremely high mass stars, and supernovae. Yes, there will be a huge burst of gamma radiation at the moment of the explosion, but that's not really fallout and a bomb of that magnitude is not going to cause much past temporary ionization.

The 8g of anti-matter we do have, plus 8g of matter required for anhilation would produce 1.4x10[sup]15[/sup]J of radiation. That is quite a bit and for only 8g of anti-matter.

Yes, it is, but that's just a number. What I was saying was that an antimatter bomb roughly comparable to a current fusion bomb would not irradiate the surrounding area. An antimatter bomb capable of the transmutation of radioactive elements out of base metals and minerals would be less a bomb and more a world-ending cataclysm, in which case I don't think you have to worry too much about fallout.

So you're honestly telling me radiation doesn't effect the nucleus of an atom with the potential of changing it... Ever heard of K capture? That will result in a change of element... and since their is radioactive isotopes of iron, oxygen, iodine and prety much any element it's a fair possibility that radioactive isotopes can result from high energy gamma ray flashes. It's the same idea as photon jumps electron to higher energy level, electron decays back and emits a new photon... gamma ray photons can do this with nucleons instead of electrons and completly destabalise nuclii.

 

[llafnwod]

snip

Yes, it is, but that's just a number. What I was saying was that an antimatter bomb roughly comparable to a current fusion bomb would not irradiate the surrounding area. An antimatter bomb capable of the transmutation of radioactive elements out of base metals and minerals would be less a bomb and more a world-ending cataclysm, in which case I don't think you have to worry too much about fallout.

So you're honestly telling me radiation doesn't effect the nucleus of an atom with the potential of changing it... Ever heard of K capture? That will result in a change of element... and since their is radioactive isotopes of iron, oxygen, iodine and prety much any element it's a fair possibility that radioactive isotopes can result from high energy gamma ray flashes. It's the same idea as photon jumps electron to higher energy level, electron decays back and emits a new photon... gamma ray photons can do this with nucleons instead of electrons and completly destabalise nuclii.

I know. Atomic nuclei are destabilized by high energy radiation. But an explosion of a non-world ending magnitude simply isn't going to create enough radioactive material to constitute a radiological hazard, and no matter-antimatter explosion would create enough to threaten anything outside of its considerable blast radius.

 

[LordOrin]

Cool thread.

Why are scientists sure of the existence of dark matter, as opposed to there being something wrong with the way we're measuring the mass of galaxies?

And how do we know the extra mass isn't coming from black holes that we haven't detected?

My research field again.

We arn't 100% sure of dark matter but it's certainly not miss measurement of galaxy masses since the luminous matter in the Galaxy just doesn't have the right shape, densit or size to produce what we're seeing. It can be put down to stuff we can't see/measure being theie but that's dark matter.

Black holes along with gravity acting differently on larger scales are the two contendors against DM. Now the things I always say are a little biased since all my work assumes DM but here goes. The cold dark matter model we use today in galactic dynamics makes several predictions that have all been observed to be true since the predictions were made so it's not just fitting the numbers to the observation. the way in which galaxies form in CDM leaves a lot of dark matter fragments in the Galaxy (in the Milkyway 100-1000 fragments of a few thousand to tens of millions of solar masses) these act to asymmertarise the galactic gravitational potential and this has been observed to be true. these clumps may be undiscovered black holes but around 4 of these clumps have been see with stars in very close proximity to where they are predicted to be, a black hole massive enought to cause the potential would be destroying these stars so visible from it's acreation disc. Another is that these fragments are distortable due to the fact they're made of man constituant parts, this has been observed when clusters as old as the Galaxy suddently have a blip in their orbit, this is thought to be the DM fragment having ebing broken by a gravitational event and so effecting the cluster.

Now their are 2 major problems in CDM to be resolved. 1)we predict many more fragments than we've ever seen, though as discussed they're really hard to see. 2) the main halo should have infinate potential at r=0, this isn't the case obviously thought their is a super massive black hole at the centre so the potential is very high.

And finally. I really really hope DM theory is correct. My work relies on it but more importantly all the work in the field for the last 50 years relies on it. If it turns out to be wrong we're being put back 50 years and worse still funding bodies and research councils will be slow to trus us again after 50 years of wasted money if DM theory is wrong.

Makes sense. I guess being able to make accurate predictions with a model is pretty compelling evidence, or at least encouraging.

There was one bit I didn't understand. Can you explain again what the second problem with CMD is?