From: Rhys 22/04/99 12:25:12 Subject: Let there be light post id: 7838 I thought I'd post this as a new topis as I think my question which was part of an earlier thread might have got lost in the thursday barrage. JR.. a photon is a fundamental particle? But surely it must be composed of something? Could you have half a photon? If I took a few trillion googleplex' worth of photons and squashed them into a ball.. what would I have? Would it produce gravity? . (Although I'm sure there'll be a sneaky answer as to why it can't be done)If I ate said ball, would I have light shining out of my... okay forget that one And finally... if indeed photons are a fundamental particle.. how many types of so called particles are thought to make up the universe? rhys From: Adrian 22/04/99 12:55:20 Subject: re: Let there be light post id: 7857 300 per current understanding with many redundancies Photons to interact with mater as per gravetational laws. Photons are no more a point particle than electrons, but they do exert a forcethey are a unit of energy and can not be explained in 3D physics From: Chris (Avatar) 22/04/99 13:20:59 Subject: re: Let there be light post id: 7866 JR.. a photon is a fundamental particle? But surely it must be composed of something? Could you have half a photon? More precisely, a photon is a quantum of energy. This is what the quantum nature of light is all about - that there is a smallest chunk of light. Actually the photon is much wider than just light, it is the fundamental quantum of the electro-magnetic field. This means the photon is the smallest chunk of X-rays, gamma rays, radio, microwave, etc all through the e/m spectrum. In the Quantum theory of ElectroDynamics (QED) the photon is treated as a particle called a boson. It is the carrier of the e/m interaction. What is a photon made of? Well, light and other e/m radiation has both particle and wave characteristics - if you like, the photon is the embodiment of the particulate characteristics. But you can't have half a photon - it is a quantum. If I took a few trillion googleplex' worth of photons and squashed them into a ball.. what would I have? Would it produce gravity? . (Although I'm sure there'll be a sneaky answer as to why it can't be done) You'd have a ball of light. Because a photon is a boson (see below) it doesn't obey the Pauli exclusion principle - which states that no two fermions can occupy the same state. So you can have a lot of photons in the same place at the same time (relatively speaking, of course.. ;o) Photons feel the gravitational interaction, as can be demonstrated by gravitational lensing - the phenomenon where light rays are "bent" around massive objects. They also interact gravitationally with other objects - albeit extremely weakly. However the fact is that the photon is massless. It is required to be so by QED, and has been observed to be so within a good deal of precision in experiment. This lends credence to the GR postulate that gravity is a warping of space-time - and that mass and energy are indeed related. And finally... if indeed photons are a fundamental particle.. how many types of so called particles are thought to make up the universe? Types? Well, according to the Standard Model of particle physics all matter is composed of quarks and leptons. These particles are all structureless point sized masses at the current level of experimental resolution. Both quarks and leptons are fermions, ie they have half-integer spin and obey the Pauli exclusion principle. Quarks bind in sets of two as mesons and three as baryons to form nuclear particles such as protons and neutrons, and other more exotic particles. There are six types of quark: up, down, top, bottom, charmed and strange. Each of these varieties also carries a type of charge called colour charge (although it is not really colour - quarks are too small). The colours are designated red, green and blue and are integral in the theory of Quantum ChromoDynamics (QCD) - QED for quarks. No free quarks are observed in nature. Leptons may be observed singly. They include the electron, muon and tau, and of course the neutrinos. Each of these particles has an antiparticle as well. In addition to the matter particles, the quantum theory includes carrier particles for each of the fundamental interactions. They all have integer spins and are called bosons. They are more precisely field quanta in the quantum field theories for each fundamental interaction. The gluon is massless and carries the strong nuclear interaction - the force which binds particles together in the nucleus and determines the stability of protons and neutrons. It is integral in the theory of QCD. The photon is massless too, and carries the electromagnetic interaction. The W and Z intermediate vector bosons are particles which carry the weak nuclear interaction - responsible for beta-decay. As yet the gravitational interaction is not renormalisable, and so is not a complete quantum theory. However the standard model (and a number of string theory variations) allow for a particle of spin 2 with zero mass which may end up being the graviton - carrier of the gravitational interaction. There are a few particle-like entities which are additional - eg the quantum of sound, the phonon and the hypothetical "mass" particle, the Higgs quantum. But the From: Chris (Avatar) 22/04/99 13:22:13 Subject: re: Let there be light post id: 7867 There are a few particle-like entities which are additional - eg the quantum of sound, the phonon and the hypothetical "mass" particle, the Higgs quantum. But these are not part of the standard model as far as I know. Hope this helps! Chris From: Rhys 22/04/99 13:45:20 Subject: re: Let there be light post id: 7875 Thanks Chris, it does indeed help.. although I'm going to have to read it all through three or four times before I come to grips with it. In regards to muons.. is it true that they exist in a slower time than our good selves? And if so, what are the implications of this? thanks again rhys From: Chris (Avatar) 22/04/99 14:52:29 Subject: re: Let there be light post id: 7899 No, dude. Can't happen. Remember - everyone and everything obeys the same laws. What you might be thinking of is simply time dilation for energetic particles. By special relativity time intervals are relative to the observer's state of motion. If a particle could be accelerated to 0.99c then that would produce a time dilation factor of just over seven. So time in the reference frame of the lab would pass 7 times quicker than in the rest frame of the particle. This assists us in observing particles which have very short lifetimes in their own frame. Hope this helps! Chris This forum is un-moderated. The views and opinions expressed are those of the individual poster and not the ABC. The ABC reserves the right to remove offensive or inappropriate messages.