Aki Posted February 21, 2004 Report Share Posted February 21, 2004 I'm curious, I have a few questions: can the speed of light be ever altered? Can we slow it down? And how much does a photon weight? thanks Link to comment Share on other sites More sharing options...
Tim_Lou Posted February 21, 2004 Report Share Posted February 21, 2004 photon is massless, it has no weight....hmm, i wonder whats the volume of it...when light travels throw some substances, it slows down, like water.normally, it travels at a constant speed. Link to comment Share on other sites More sharing options...
deamonstar Posted February 21, 2004 Report Share Posted February 21, 2004 light only travels at "light speed" in a vaccuum. its realative velocity slows when travelling through a medium such as our atmosphere or water or glass etc... etc... here is a link you may find interesting:stop light Link to comment Share on other sites More sharing options...
Aki Posted February 22, 2004 Author Report Share Posted February 22, 2004 well how can something be completey massless? so a photon doesn't even weight 10000000000000 times less than (I don't know) the lighting thing on earth? Link to comment Share on other sites More sharing options...
deamonstar Posted February 22, 2004 Report Share Posted February 22, 2004 when doing basic calculations of theories where the mass of a photon isn't a critical variable, it would be allright to assume a value of zero for the mass of a photon. however, when we delve into calculations of theories based on special realativity or quantum mechanics, where the mass of a photon becomes more critical, we must give a non-zero value to avoid anomolies such as infinities or absolute zero's. but, what is this non-zero value, and how can it be determined? an ingenius experiment carried out by Jun Luo and his colleageus at Huazhong University of Science and Technology in Wuhan, China using a very sensitive torsion balance (a device with rotational torque) have been able to determine the mass of a photon. they aimed a beam of light at the apparatus, for which the value of the torque (or rotational energy) of it is known. when the photons hit the device, there is a measurable increase in the overall torque. this method is a 20-fold increase in the accuracy to determining the value of the mass of a photon over previous methods for determining the photon's mass. the newly determined estimate for thenon-zero valueof the mass ofa photonis 10<SUP>-51</SUP> grams or 7 x 10<SUP>-19</SUP> electron volts. for more info, go to the following link: photon mass Link to comment Share on other sites More sharing options...
halogenesis Posted February 23, 2004 Report Share Posted February 23, 2004 if you ever visit http://www.madsci.org, and search their archives, you'll find a large amount of discussion to your questions about the whole massless photon debate (of course, there are MANY other topics). There was a recent discussion by a post-doc named Phil Marsden where he imparts his views on photon interactions. The most interesting thing I found was this new field of study on QUANTUM HOLOGRAPHY... here are some interesting links http://unisci.com/stories/20014/ 1126013.htm http://www.aip.org/enews/physnews/2001/split/566-1.html I got these sites from Marsden's article.... enjoy them! They are interesting! Link to comment Share on other sites More sharing options...
Tim_Lou Posted February 23, 2004 Report Share Posted February 23, 2004 i found something in some website: Q: Do photons have mass? If not, why does the gravitational field of a star bend passing light? A: No, photons do not have mass according the present definition of mass. The modern definition assigns every object just one mass, an invariant quantity that does not depend on velocity, says Dr. Matt Austern a computer scientist at AT&T Labs Research. Under this definition, mass is proportional to the total energy, Eo, of the object at rest. "A particle like a photon is never at rest and always moves at the speed of light; thus it is massless," says Dr. Michael S. Turner, chair of the Department of Astrophysics at the University of Chicago. What about experimental evidence? Experiments don't determine exact quantities because of small errors inherent in making measurements. We have, however, put an upper limit on the photon rest mass. In 1994, the Charge Composition Explorer spacecraft measured the Earth's magnetic field and physicists used this data to define an upper limit of 0.0000000000000006 electron volts for the mass of photons, with a high certainty in the results. This number is close to zero; it is equivalent to 0.00000000000000000000039 times the mass of an electron (the lightest particle), says Turner. Link to comment Share on other sites More sharing options...
Tim_Lou Posted February 23, 2004 Report Share Posted February 23, 2004 hmmm, if photons have mass, and it travels at the speed of light.....how is it possible??how can "massive" particals travel at the speed of light??? probably, the "mass" of photons is due to its energy. mass and energy....probably the same thing... Link to comment Share on other sites More sharing options...
Aki Posted February 23, 2004 Author Report Share Posted February 23, 2004 Okay, photons are not "massless". They have a mass. So if we find something lighter than a photon, it'll be able to travel faster than light! But it is said that NOTHING can travel than the speed of light. So are photons the lightest thing we can ever find, or is there something else ligher, which can travel faster? Link to comment Share on other sites More sharing options...
wavelength? Posted February 23, 2004 Report Share Posted February 23, 2004 If E=MC2 and the speed of light slows down when passing through a medium such as water or the earths atmosphere then the photon should gradually gain mass as it slows it's velocity. and if a stars atmosphere such as the gas it's giving off or even its magnetic field could be considered a medium, then the photon should slow down and gain mass and gravity would begin to pull on it, therefor bending light.~ Link to comment Share on other sites More sharing options...
Tim_Lou Posted February 23, 2004 Report Share Posted February 23, 2004 i dont believe that photons have mass. its probably some experimental error. atoms are made of electrons, protons and neutrons as we all know.and protons and neutrons are made of quarks.but the total mass of quarks doesnt equal the mass of protons and neutrons, it is a very small % of the mass of protons and neutrons. then where does the rest mass comes from?it is due to the energy in it. so, my conclusion is this, photon has mass, probably it is due to its energy. Link to comment Share on other sites More sharing options...
TINNY Posted March 2, 2004 Report Share Posted March 2, 2004 And, while everything in the physical universe has some mass greater than zero, which is a necessary characteristic for existence in the material world, light has no mass at all. As you approach the speed of light mass increases, at the speed of light mass is infinite. Regardless of how tiny the amount of mass you begin with, that mass rises to infinity at the speed of light. Since photons travel at the speed of light and do not reach infinite mass it means that they had zero mass to begin with, and a light therefore does not actually exist in the material world.read more Link to comment Share on other sites More sharing options...
PIB28 Posted March 18, 2004 Report Share Posted March 18, 2004 The slit experiment showed that photons can behave as particles. Don't ALL particles have mass? So, if a photon has mass, wouldn't it take infinite energy to accelerate it to the speed of light? This one has me confused and saying there are "massless particles" seems like a bullshit answer -- but what do I know? Link to comment Share on other sites More sharing options...
wavelength? Posted March 18, 2004 Report Share Posted March 18, 2004 I have posted a reply in the thread "matter and energy" which may help you out. Since all matter is made up of light that occupies space time, then when you try to accelerate matter to the speed of light what you accually would be doing is trying to take the spin of light in the matter and attempt to make light go faster than the speed of light in the forward precession. Since light can not go faster than itself what you would end up with is infinite mass, and it would also take infinite energy to try and accelerate matter to the speed of light since it is impossible. What you would have to do to get something to travel at the speed of light is take the light that is in rotation in the matter and convert in back to its original form, which is linear. This has not been done yet, it is improbable but not impossible. Link to comment Share on other sites More sharing options...
Spinner Posted April 4, 2004 Report Share Posted April 4, 2004 Under the wave theory of matter, matter is described as standing waves in a wave-structured universe. The most common "proof" of existence of mass, such as inertia, gravity and space-time curvature may therefore just be observed properties of a more fundamental phenomenon. In fact mass itself might just be an observed derivative property as such, and may not deserve a primary measuring unit (gram). The fact that mass changes at relativistic speeds is in support of such a view. An increasing mass on acceleration at high speeds might happen to be a set of consistent observations and explanations that might actually be sitting within a superset of observations and explanations by a higher and more unifying theory (wave theory), with the difference either not yet observed by human science, or already observed but not attributed a consistent and commonly recognised scientific theory or discipline yet. No different to how observations of Newtonian mechanics is within the Einsteinian superset. So for Einstein, the increasing mass module to his overall theory is simply very convenient. We simply have not had sufficient empirical observations to conclusively prove anything solid in this "increasing mass" phenomenon. No different to how Newtonian mechanics explained all observations until an inconsistency was found observing planetary movement with a higher level of precision. The "Stopping Light" article listed earlier in the thread, which saw light being "stored" in matter spin also makes a parallel link between matter and light, and not entirely different to the manner e=mc^2 links the pair. Link to comment Share on other sites More sharing options...
WebFeet Posted April 4, 2004 Report Share Posted April 4, 2004 The most common "proof" of existence of mass, such as inertia, gravity and space-time curvature may therefore just be observed properties of a more fundamental phenomenon. In fact mass itself might just be an observed derivative property as such, and may not deserve a primary measuring unit (gram). The electron and the positron Both of them have the same mass, the same spin and the same amount of energy - 0.5MeV.The only difference is the charge. The electron is negative, the positron (the anti particle of the electron) is positive. Bring the two of them together and they annihilate each other resulting in two photons, each of 0.5MeV. Every other property that distinguished the electron from other particles has gone. Likewise with the positron. The simplest way to view this is that mass, spin and charge are all properties of the energy that went into making up each of the particles. The mass and spin would have had the same values, so would not have cancelled each other out.The charge, on the other hand, was opposite and could have cancelled out the other. This seems to imply a hierarchy to the properties of the particles.1. Energy2. Configuration of the energy - charge3. The properties relating to the configuration - mass Without some form of configuration of the energy, there can be no mass - the photon. Once the energy has some form of configuration it becomes a system, comprising of more than just its component energy. Link to comment Share on other sites More sharing options...
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