ps3 Posted October 8, 2008 Share Posted October 8, 2008 do they violate causality since they travel faster than light and violate conservation? Link to comment Share on other sites More sharing options...
Severian Posted October 8, 2008 Share Posted October 8, 2008 They don't travel faster than light, so, no, they don't violate causality. Link to comment Share on other sites More sharing options...
ps3 Posted October 15, 2008 Author Share Posted October 15, 2008 what do virtual particle's violate? Link to comment Share on other sites More sharing options...
timo Posted October 15, 2008 Share Posted October 15, 2008 They do not obey the energy-momentum relation that a free particle of the respective field would have. Link to comment Share on other sites More sharing options...
ps3 Posted October 16, 2008 Author Share Posted October 16, 2008 why can they violate causality? Link to comment Share on other sites More sharing options...
Severian Posted October 16, 2008 Share Posted October 16, 2008 No. Interestingly in Quantum Field Theory you can show that particles with positive energy always must move forwards in time in order to preserve causality. This seems fair enough, but perhaps more oddly, you can also show that particles of negative energy must flow backwards in time to preserve causality (weird huh?). This is actually where antiparticles come from since a negative energy particle moving backwards in time is actually identical to a positive energy antiparticle moving forwards in time. This is called the Feynman-Stueckleberg interpretation. Link to comment Share on other sites More sharing options...
ps3 Posted October 16, 2008 Author Share Posted October 16, 2008 (edited) so what is really going back in time? this is what confuses me with anti particle and particle time travel,back in time sort of thing. Edited October 16, 2008 by ps3 Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted October 16, 2008 Share Posted October 16, 2008 Nothing's going back in time. Antiparticles don't violate causality. Link to comment Share on other sites More sharing options...
ps3 Posted October 16, 2008 Author Share Posted October 16, 2008 i read that virtual particle's CAN travel faster than light,because of the uncertainty principle? Link to comment Share on other sites More sharing options...
Gilded Posted October 16, 2008 Share Posted October 16, 2008 All of it falls within the bounds of the uncertainty principle. Virtual particles can violate rules all they want as long as they don't get caught, so to speak. Regarding causality, information isn't transmitted at superluminal speeds even by virtual particles with negative energies as noted by Severian. Link to comment Share on other sites More sharing options...
ps3 Posted October 17, 2008 Author Share Posted October 17, 2008 so this mean's cause and effect is safe from being violated? Link to comment Share on other sites More sharing options...
ps3 Posted October 21, 2008 Author Share Posted October 21, 2008 can virtual particle go faster than the speed of light? Link to comment Share on other sites More sharing options...
Kyrisch Posted October 22, 2008 Share Posted October 22, 2008 No. Virtual particles have normal mass. Theoretically, particles with imaginary (in the mathematical sense) mass can (called "tachyons"). Link to comment Share on other sites More sharing options...
ps3 Posted October 22, 2008 Author Share Posted October 22, 2008 i have some link's where it's said they DO violate causality. http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html http://www.ucolick.org/~mountain/AAA/030718.html Link to comment Share on other sites More sharing options...
swansont Posted October 23, 2008 Share Posted October 23, 2008 i have some link's where it's said they DO violate causality. http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html http://www.ucolick.org/~mountain/AAA/030718.html First link: you misread it. "The virtual particle didn't "transmit" any information that I didn't have already; it is useless as a means of faster-than-light communication." That translates as: doesn't violate causality. Second Link: "First off a disclaimer: I'm not a particle physicist, and although I have a basic understanding of Quantum Field Theory, I can by no means claim to be an expert on virtual particles" The "violation" he then quotes is the HUP. Link to comment Share on other sites More sharing options...
ps3 Posted October 25, 2008 Author Share Posted October 25, 2008 what is the longest time a virtual particle can last? Link to comment Share on other sites More sharing options...
swansont Posted October 25, 2008 Share Posted October 25, 2008 what is the longest time a virtual particle can last? It depends on its energy. The longest time approaches infinity. Link to comment Share on other sites More sharing options...
ps3 Posted October 25, 2008 Author Share Posted October 25, 2008 so it can last infinitly? Link to comment Share on other sites More sharing options...
Gilded Posted October 26, 2008 Share Posted October 26, 2008 so it can last infinitly? I think that would mean the particle has 0 energy. So no. Link to comment Share on other sites More sharing options...
Kyrisch Posted October 26, 2008 Share Posted October 26, 2008 so it can last infinitly? It can last as near to infinity as the particle's energy is near zero. [math]\Delta E \Delta t \leq \hbar[/math] Where [math]E[/math] is energy, [math]t[/math] is duration, and [math]\hbar[/math] is Dirac's constant. Link to comment Share on other sites More sharing options...
timo Posted October 26, 2008 Share Posted October 26, 2008 Wouldn't that depend on the value of [math]\Delta[/math], too? Link to comment Share on other sites More sharing options...
Severian Posted October 26, 2008 Share Posted October 26, 2008 The probability of decay is proportional to the Breit-Wigner distribution: [math]\frac{m \Gamma}{\left(E^2-|\vec{p}|^2-m^2 \right)^2 + m^2 \Gamma^2}[/math] where [math]\Gamma[/math] is the particle width and I have neglected the [math]c[/math]'s. Link to comment Share on other sites More sharing options...
ps3 Posted October 27, 2008 Author Share Posted October 27, 2008 The probability of decay is proportional to the Breit-Wigner distribution: [math]\frac{m \Gamma}{\left(E^2-|\vec{p}|^2-m^2 \right)^2 + m^2 \Gamma^2}[/math] where [math]\Gamma[/math] is the particle width and I have neglected the [math]c[/math]'s. what does this all mean? i was told by a friend that causality is violated but since we can't see it happening it cannot affect us.is this true? Link to comment Share on other sites More sharing options...
ps3 Posted October 30, 2008 Author Share Posted October 30, 2008 ive been told that virtual particle's are allowed to travel faster than light due to uncertainity principle. here is a link where i got my info. http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html Link to comment Share on other sites More sharing options...
Riogho Posted October 30, 2008 Share Posted October 30, 2008 They can go as fast as they frikkin want to, they don't exist. Link to comment Share on other sites More sharing options...
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