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anuj
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How much do we know about particles and antiparticles? Can we say that the two class of particles follow all the known laws of physics. i.e. no deviation or violation of known laws.
anuj said:How much do we know about particles and antiparticles? Can we say that the two class of particles follow all the known laws of physics. i.e. no deviation or violation of known laws.
anuj said:How much do we know about particles and antiparticles? Can we say that the two class of particles follow all the known laws of physics. i.e. no deviation or violation of known laws.
anuj said:Truely speaking, we understand the physics (QM in general and relativity in particular) of positive energy particles moving forward in time. We do understand the negative energy particles or the particles moving backward in time as antiparticles to some extent.
For example, Can we say for sure with experimental support that the antiparticles do not violate laws of electrodynamics, heavenly bodies made up of antiparticles will follow Newtons gravity laws, Physical meaning of moving backward in time (not the mathematical formulation).
mathman said:There is an extremely small difference in properties between particles and anti-particles. At the big bang, particles and anti-particles were born in equal number, but because of this diffference, there ended up a slight excess of particles, which make up the planets, stars, etc. Although physicists have discovered some of these differences, the final result (particle excess) is not fully understood.
Try searching the web for baryogenesis.Adrian Baker said:Are there any good resources on this on the 'net that you know of?
Thanks
Look for articles by Michael Turner on arXiv. For starters, astro-ph/0202005, 0202007, 0202008. (These are all more or less the same).Are there any good resources on this on the 'net that you know of?
Thanks
ZapperZ said:If antiparticles "violate" the laws of electrodynamics, your modern electronics would NOT work. In condensed matter physics, the "holes" in your p-type semiconductors (part of your pn junction) are the antiparticles of electrons. The physics that describe electron-hole creation is IDENTICAL to the physics of electron-positron pair.
Zz.
anuj said:The physics of electron-hole may be identical to electron-positron but I suspect we can make a conclusion that a hole is nothing but a positron. If it is so, why do we need to make big expensive particle colliders to create antiparticles just to study their physical properties. Cant we do the same using some simple semiconductor devices.
Secondly, the negative energy should mean an imaginary mass that in turn should mean that two negative energy particles should repulse (Newtons gravity, a week field as compared to electromagnetic field)
Is it right to consider the absence of -ve energy as +ve energy which is an antiparticle. i.e. the absence of an imaginary mass as a +ve mass particle.
Any reference for the comparison between hole and positron.
ZapperZ said:It is because you can't study "holes" outside of a many-body interaction of the material, whereas as you can with positrons. There are things you can study with positrons that you can't study with holes, and there are things you can study with holes that you can't study with positrons.
Zz.
anuj said:It is difficult to prevent a positron from interacting with an electron as the two quickly annihilates resulting in a photon of energy E following the Einstein's famous mass energy equation. How come, in a many body interaction the same positron finds it easy to stay alive (no anihilation).
Take the example of a semiconductor laser. The electron-hole recombination too results in emission of a photon but this time the energy of photon is equal to the quantum state of electron to hole transition. If a hole is same as positron, why the emission of light here is not according to Einstein's equation.
anuj said:The physics of electron-hole may be identical to electron-positron but I suspect we can make a conclusion that a hole is nothing but a positron.
gptejms said:I guess what anuj is trying to ask when he asks if anti-particles violate physical laws is this---is an anti-particle really a particle (of opposite parity) going back in time?(CPT)
anuj said:If it is so, why do we need to make big expensive particle colliders to create antiparticles just to study their physical properties.
Cant we do the same using some simple semiconductor devices.
ZapperZ said:The laws of physics work the same way either forward or backwards in time (let's not get CP violation into this). So why would it matter if this is a particle going forward or backwards in time?
Take note that there's nothing to prevent me from also equating a real particle moving forward in time with an antiparticle moving backwards in time.
But this is all moot and meaningless until someone can point to me the evidence that would lead to the original question of this thread in the first place. What IS the evidence that our laws of physics do NOT work on particles and antiparticles? I have tried to described as much as I can why we KNOW they work. It seems that the assertion that they MIGHT not work are simply based on speculation and "witch-hunting" without any kind of physical justification.
Zz.
gptejms said:Zz,I was only trying to guess what anuj possibly meant by violation of physical laws by particles/anti-particles---onle he can clarify on that.But your statement 'how does it matter...' is a bit of an over-statement.To say that an equation has time reversal symmetry is not the same as saying that the particle actually goes back in time--so it does matter.
anuj said:Secondly, the negative energy should mean an imaginary mass that in turn should mean that two negative energy particles should repulse (Newtons gravity, a week field as compared to electromagnetic field)
gptejms said:Since the e-p pair is short-lived
gptejms said:Zz,just for the sake of argument consider this:-in an electron-positron pair,a virtual positron could actually be an electron going back in time(or the other way round).Since the e-p pair is short-lived, this interpretation would be consistent with the time-energy uncertainty relation.
vanesch said:But positrons by themselves can live quite a long time, you know. I remember that in the HERA ring, (where protons were collided onto positrons), they kept the positrons circling for 8 hours (and then they dumped the beam).
BTW, the reason why positrons were used (while the machine was originally designed to use electrons) was quite funny. At the startup of HERA, the lifetime of the electronbeam was quite short, and they found out that some ion pumps which kept the ring under a high vacuum lost positive ions, and these were attracted to the space charge of the electron beam, thus finishing IN the beam and steadily making the electrons get lost. So they decided to switch to positrons, and the problem was solved :-)
cheers,
Patrick.
gptejms said:Guys,I was referring to the loop in a Feynman diagram which is a virtual process(!)--all I said was that the short-lived electron-positron pair in such a scenario may be given the kind of interpretation I gave above.
gptejms said:Guys,I was referring to the loop in a Feynman diagram which is a virtual process(!)--all I said was that the short-lived electron-positron pair in such a scenario may be given the kind of interpretation I gave above.
marlon said:You need to be careful with what you say here. Although i get the point you are making, it needs to be said that loops in QED and QCD correspond to self-energy terms. Indeed a short-lived electron positron pair can be created and "killed" shortly after. You do not need loops for that though since this process happens constantly in the vacuum, ie vacuum fluctuations of QFT. When enough energy is available this virtual pair can become real and "long-living".
marlon
ZapperZ said:Is there a reason why you are going out of your way to pick one of the most EXOTIC, unlikely, and frankly, the strangest way to generate a positron?
anuj said:I started this thread in view of an article I read in Scientific American, Sept. 2004 issue. Two expt., ATHENA and ATRAP, at CERN are underway to test the spectroscopic properties of hydrogen and antihydrogen atom (see the SA issue). The experiments are conducted to test the CPT violation and consequently the Lorentz violation.
If we are so sure about the physics of particle-antiparticle then why do we need to test the CPT. Do we expect an atom to behave differently then an antiatom or matter as compared to antimatter (any comments ZZ)?
In a semiconductor, the position of a hole is below Fermi energy level whereas electron is above it. In contrast, the position of a Positron is below 0 i.e. -ve energy where as an electron has +ve energy. That is why electron-hole pair results in radiation of few eV, while electron-positron recombination results in a high energy radiation. Although the physics (explanation) of electron-hole looks similar to electron-positron, one really need to prove the similarities experimentally.
Is there any experimental proof where a large number of electrons and positrons are trapped and made to behave as they do in a semiconductor material. What I mean to say is an electron-positron recombination in vacuum results in emission of radiation following the Einstein's mass energy eqn. Can we experimentally prove that in a many body problem involving actual electrons and positrons, their recombination will be according to electron-hole recombination process.
anuj said:Is there any experimental proof where a large number of electrons and positrons are trapped and made to behave as they do in a semiconductor material. What I mean to say is an electron-positron recombination in vacuum results in emission of radiation following the Einstein's mass energy eqn. Can we experimentally prove that in a many body problem involving actual electrons and positrons, their recombination will be according to electron-hole recombination process.
anuj said:Thanks ZZ. My question is answered to some extent. The last question regarding electron-hole and electron-positron still remains to be answered fully. I hope you can cite reference to some already performed expts to prove the positron-hole equivalance.
ZapperZ said:Look in a technique called inverse photoemission.
Zz.
anuj said:The inverse photoemission technique is used to study the unoccupied electronic states in solids. This is done using the ultraviolet or soft X-rays. Which basically means study of electrons-holes. What I am asking is the experimental proof for a large number of electrons-positrons made to behave as though they are in a semiconductor material showing similar characteristics as electrons-holes. An inverse photoemission technique can probably be useful here provided a gamma ray (>400kev) is used to generate an electron hole pair. Any experiment performed in that direction.
Particles and antiparticles are two types of subatomic particles that make up the building blocks of matter. They have the same mass and spin, but opposite electric charge and other quantum numbers.
Particles and antiparticles can be created through high-energy collisions, such as those that occur in particle accelerators. They can also be created through certain types of radioactive decay.
When a particle and antiparticle meet, they can annihilate each other, releasing energy in the form of gamma rays. This process is known as annihilation.
Particles and antiparticles play a crucial role in understanding the early universe and the processes that govern it. They also help explain the fundamental forces that govern the interactions between particles.
The main difference between matter and antimatter is that they have opposite charges. Matter is made up of particles with positive charges, while antimatter is made up of particles with negative charges. This difference is what allows them to annihilate each other when they come into contact.