Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 17/06/2008 22:22:02
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I've been reading about particle physics and the LHC again, and it suddenly occured to me that there is a gaping hole in my understanding.
There are electrons, quarks, gauge bosons etc. Some of these exist all the time, some have a transient existence to enable them to mediate forces. But what about the massive particles (≥1TeV) that may be detected in experiments at the LHC?
Are these particles in existence the same as electrons etc are? Are they created by the collisions? Are they composites that decay into particles from the Standard Model? Please enlighten me.
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There's a ton of different theories on where they come from. In general, however, really massive particles are thought to be the the result of high energy being concentrated in a small area, such as you get in a particle accelerator or just after the big bang. The same goes for the particles of energies higher than 1 TeV as far as I know (but I don't keep up on the theories). They should generally decay quickly. Even when you're dealing with the particles in the standard model so far, you don't detect the really massive ones directly. They decay so quickly that what you detect is a "jet" of less massive decay products coming out of the collision. When you trace the paths of all the decay products back, you can figure out what created them and therefore "detect" the massive particle.
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jpetrucelli - thanks. But that does raise another couple of questions.
In the beginning there were quarks, electrons, photons, neutrinos, etc which smashed into each other to produce protons and the like. Now we smash particles together in attempts to create other particles. Did the particles we are attempting to create exist before quarks, electrons, etc and decay into them?
Originally, was there, maybe, one Big Momma type of particle that decayed into less massive particles which, in turn, decayed into particles that were less massive still and so on until we get the particles we are familiar with today?
Could the initial decay of such a particle be responsible for, or coincide with, the symmetry-breaking that caused the separation of gravity from the other forces (if all the forces were indeed originally united)?
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Doc & JP
Are planets and stars the ultimate particles? And does the decay of stars through fusion seed the Universe with all of the smaller particles? Do collisions of Massive particles like meteors and comets, cause explosions, and huge collisions of meteors and comets cause the debris we see on differing trajectories fly in the face of a unified expansion of the Universe? But then there is the possibility of the billiard ball effect to create different trajectories after collisions. But without a cushion to bounce off we would still have a problem explaining how two comets could be travelling in the opposite direction. Then there is gravity from the even larger particles, planets and suns. These could easily provide us with the billiard table cushion and change the direction of the comet or meteorite like a ball in a pinball machine. Here on earth however, we observe small particles under the influence of the Earths mass, so what we are observing may not be the same if in the space between planets? But given the rotation of the planets would we still be left with a predictable path for these mega objects? And does this apply to very small particles also? Like you say each answer opens up many more questions.
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Doc & JP
Are planets and stars the ultimate particles?
I suppose that depends on your definition of a particle. But, in any case, what about black holes?
And does the decay of stars through fusion seed the Universe with all of the smaller particles?
I'm not sure about all of the smaller particles; but certainly some.
Do collisions of Massive particles like meteors and comets, cause explosions, and huge collisions of meteors and comets cause the debris we see on differing trajectories fly in the face of a unified expansion of the Universe?
I don't follow the logic of that. I don't see that objects have different trajectories has any bearing on a unified expansion.
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The idea of elementary particles is that they aren't made up of other, smaller particles. Protons, atoms, molecules, and planets are all made up of tinier "bits." When you get down far enough, the most fundamental things you can find are the elementary particles of the standard model, which are what DoctorBeaver was asking about I believe.
Exactly what you believe about these particles depends on what theories you believe, however. Most of the standard model work says (as far as I know) that these particles we're trying to make in the LHC were indeed around early on in the universe. They vanish quickly if there's not a lot of energy about, so that's why we don't see them anymore. We're now trying to simulate the extremely high energies just after the big bang in order to see them.
Instead of saying that all the particles we see today are babies of the big mama particle early on, I think it might be more accurate to say that all the particles today were born from the big mama energy early on, since energy gives rise to all particles. Once the universe expanded, there was less energy per volume of space, and so massive particles just weren't sustainable. However, I know there's plenty of theories that go beyond this to explain how gravity works and why we see some of the symmetry breaking. I don't know the details of most of them, and none have won the day yet... but the kinds of experiments done at the LHC may help shed light on which ones are right.
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When you get down far enough, the most fundamental things you can find are the elementary particles of the standard model, which are what DoctorBeaver was asking about I believe.
Yes. Those, the more massive particles they hope to detect at the LHC & those more massive still that we could never detect as the energy required is too enormous.
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Perhaps explosions was a bit too dramatic but certainly an impact large enough to send fragments off in different directions. I guess what I was trying to say is that we can see huge objects in space, stars, planets, comets meteors and we can hold some of them in our hands and if we look close enough we can even see the particles that make them up. And I accept this because it is plain for everyone to see. My problems begin when people invent wimps that no one has ever observed, yet they fly right through the earth as regular as clockwork. Black holes and dense matter. These I cannot see smell or touch and neither can anyone else so why rely so much on what no one has yet observed?
http://science.nasa.gov/headlines/y2001/ast12jan_1.htm
"By detecting very little energy from these black hole candidates, we have new proof that event horizons exist," said Michael Garcia of the Harvard-Smithsonian Center for Astrophysics, Cambridge, MA. "It's a bit odd to say we've discovered something by seeing almost nothing, but, in essence, this is what we have done."
Its statements like this that are great for the next Star Treck Movie but do little to convince me of the existence of these obscure phenomena.
JP I understood Doc’s interest in particles. And thank you for your insight into how it all is thought to work. And from your post I can see you are also not completely convinced either.
Andrew
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I believe (that is AFAIK - not as in an issue of faith) that there weren't any discrete particles until after the initial inflation phase of the BB - the very first stages seem to have been just energy, space & time.
Given what we know atm, it's not unreasonable to think of BHs as finite pre-BB states.
I'm not neccesarily saying that I do think that, but it's plausible - there seems to be an equal degree of breakdown in physics.
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Let me see if I've got this right...
It takes enormously high energy to create massive particles; but if the energy gets too high, we're left with just energy (as in immediately after the BB). But I believe that were we able to create enough energy to probe the smallest distances, that energy would collapse into a black hole.
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I'm not sure you can make either of those assumptions i.e. the energy getting too high and reverting back to energy while trying to create massive particles, or that enough energy would collapse into a BH, because the time direction is different when compared with how it happened in the BB.
Perhaps you could imagine it as the BB being like funnel working the wrong way, with the time direction showing the direction of flow - putting another funnel after it, in the time direction, to re-concentrate it isn't performing the opposite action because the time direction hasn't been reversed.
Although I guess we could hypothesise a massive particle who's lifetime is less than the Planck Time, so we could never see it, if it could exist.
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I've read in several textbooks that energy that is high enough to probe the Planck scale will collapse into a BH.
When I said about energy being too high for particles to form, I was talking about in the immediate aftermath of the BB.
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Yeah - it seems that a photon energetic enough to probe a Planck sized object could spontaneously create a Planck sized particle that would have sufficient mass to become a BH. However, would not a Planck-sized BH also be the smallest BH that could be created? If so, it should evaporate very quickly.
A possible factor in the very early stages of the BB is that so many interactions were going on at any one instant that contradictory interactions may have been occuring simultaneously i.e. while an interaction might have been creating a particle, another simultaneous interaction may have been destroying it, whilst yet another might have been trying to create an entirely different particle. For particles to be successfully created the interactions must be allowed exclusivity and sufficient time to complete, but with a high enough energy density and too little time it's possible that that couldn't happen.
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Yeah - it seems that a photon energetic enough to probe a Planck sized object could spontaneously create a Planck sized particle that would have sufficient mass to become a BH. However, would not a Planck-sized BH also be the smallest BH that could be created? If so, it should evaporate very quickly.
Indeed. I believe I read that they would only exist for 10-43 seconds.
A possible factor in the very early stages of the BB is that so many interactions were going on at any one instant that contradictory interactions may have been occuring simultaneously i.e. while an interaction might have been creating a particle, another simultaneous interaction may have been destroying it, whilst yet another might have been trying to create an entirely different particle. For particles to be successfully created the interactions must be allowed exclusivity and sufficient time to complete, but with a high enough energy density and too little time it's possible that that couldn't happen.
That sounds quite feasible.
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I should point out that that's just a hypothesis and not a theory, although some number crunching should show if it actually is feasible or not.