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If we consider time dilation and length contraction using special relativity does the photon therefore have infinite length contraction and time dilation? If so is that why we see it as a massless particle?

The photon, traveling at the speed of light does have mass,

Light has been slowed and observed....sorry, you cannot view external links. To see them, please REGISTER or LOGINThe question is why light travels at c in the first place.

I can see the point particle principle

but if mass increases as we reach light speed then why is the photon not massive?

Quote from: hubble_bubble on 04/09/2012 16:06:00Light has been slowed and observed.http://en.wikipedia.org/wiki/Slow_light [nofollow]The question is why light travels at c in the first place. c is just a number, because it depends on the units of measure; it is 1 or it is 0.000001 or any number, in other units. The question is another: why light speed is finite?QuoteI can see the point particle principle What is this principle?Quotebut if mass increases as we reach light speed then why is the photon not massive? On the contrary! As another has written, if it had mass, it couldn't reach light speed.

Light has been slowed and observed.http://en.wikipedia.org/wiki/Slow_light [nofollow]The question is why light travels at c in the first place.

Yes we can define c as 1 for convenience in equations. Point particles are idealized particles used in equations. There is a dichotomy inherent in what we consider mass. The fermions which make up matter and a boson like the photon behave in distinct ways at velocity. The Fermions can never act like a photon as instead of its mass decreasing with increasing velocity it increases so will never reach a zero point mass. It is going in the wrong direction. The photon is immediately in the correct state when emitted.

Yes, all this is true because it matches our observations of the universe. So what's the problem? Why should we be troubled that special relativity, which is designed to cover the reference frames only of massive particles, doesn't include reference frames for massless particles? It still covers all the cases we can measure, since we have mass and our detectors have mass, and produces very accurate results.

There is a dichotomy inherent in what we consider mass. The fermions which make up matter and a boson like the photon behave in distinct ways at velocity. The Fermions can never act like a photon as instead of its mass decreasing with increasing velocity

so will never reach a zero point mass.

It is going in the wrong direction.

The photon is immediately in the correct state when emitted.

having no mass, per se, is the main reason a photon can travel at the speed of light, and thereby establish that rule. if a photon had mass, it could not achieve the speed of light.... I believe....lol

The only catch is that we don't know how to describe what a massless detector would see... but building a massless detector doesn't even make sense (since all its particles would fly away from each other at the speed of light!)

Quote from: hubble_bubble on 04/09/2012 21:40:44There is a dichotomy inherent in what we consider mass. The fermions which make up matter and a boson like the photon behave in distinct ways at velocity. The Fermions can never act like a photon as instead of its mass decreasing with increasing velocity Mass decreasing with velocity? Even if you talked of "relativistic mass" (which is not "mass") I can't understand how it could decrease with increasing velocity.Quoteso will never reach a zero point mass.What is a "zero point mass"?Quote It is going in the wrong direction.What does it mean?Quote The photon is immediately in the correct state when emitted.What does it mean?

Quote from: JP on 05/09/2012 02:27:48 The only catch is that we don't know how to describe what a massless detector would see... but building a massless detector doesn't even make sense (since all its particles would fly away from each other at the speed of light!) Infact a massless detector would be, e.g., another photon. Since Even if photon-photon scattering hasn't been observed yet (as far as I know), because of its exceedingly low cross section, it shouldn't be anything particularly bizarre.

I don't think that we would detect anything in the reference frame of a photon as theoretically the time dilation would be infinite. This would effectively stop time in that frame. Looking at it this way if we ever could reach light speed we would experience nothing until we impacted some other object. Even then the impact would preclude any interaction with the universe as our matter would vaporize.

The important point is the effect of gravity on light. Gravity affects mass, which suggests that photons must have mass. If not then there is some component missing from the laws of physics. This is fundamental.

A slight clarification about the difference between Mass and Rest Mass:The photon, traveling at the speed of light does have mass,and is deflected by a gravitational well like the Sun

Quote from: evan_au on 04/09/2012 12:17:51A slight clarification about the difference between Mass and Rest Mass:The photon, traveling at the speed of light does have mass,and is deflected by a gravitational well like the Sun photons do not have any "mass' massA measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies. a Photon does not affect other particles gravitationally, cause it has zero mass....No, photons do not have mass, but they do have momentum. The proper, general equation to use is E2 = m2c4 + p2c2 So in the case of a photon, m=0 so E = pc or p = E/c. On the other hand, for a particle with mass m at rest (i.e., p = 0), you get back the famous E = mc2. ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

Quote from: evan_au on 04/09/2012 12:17:51A slight clarification about the difference between Mass and Rest Mass:The photon, traveling at the speed of light does have mass,and is deflected by a gravitational well like the Sun photons do not have any "mass' massA measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies. a Photon does not affect other particles gravitationally, cause it has zero mass....No, photons do not have mass, but they do have momentum. The proper, general equation to use is E2 = m2c4 + p2c2 So in the case of a photon, m=0 so E = pc or p = E/c. On the other hand, for a particle with mass m at rest (i.e., p = 0), you get back the famous E = mc2. http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/960731.html [nofollow]http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html [nofollow]http://www.weburbia.com/physics/photon_mass.html [nofollow]http://home.fnal.gov/~pompos/light/light_page31.html [nofollow]The photon is massless,[Note 2] has no electric charge,[12] and is stablehttp://en.wikipedia.org/wiki/Photon [nofollow]

Quote from: Emc2 on 06/09/2012 11:37:04Quote from: evan_au on 04/09/2012 12:17:51A slight clarification about the difference between Mass and Rest Mass:The photon, traveling at the speed of light does have mass,and is deflected by a gravitational well like the Sun photons do not have any "mass' massA measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies. a Photon does not affect other particles gravitationally, cause it has zero mass....No, photons do not have mass, but they do have momentum. The proper, general equation to use is E2 = m2c4 + p2c2 So in the case of a photon, m=0 so E = pc or p = E/c. On the other hand, for a particle with mass m at rest (i.e., p = 0), you get back the famous E = mc2. ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN I am not familiar with this equation. For E2 = m2c4 + p2c2 what is p? I am also assuming m^2c^4 + p^2c^2.

If the photon has no mass. How can it react on surfaces whith force. In the case of vanes of mill under a vacuum (crookes radiometer)Quoteor in the case of this link ...sorry, you cannot view external links. To see them, please REGISTER or LOGINOptical tweezers are capable of manipulating nanometer and micrometer-sized dielectric particles by exerting extremely small forces via a highly focused laser beam. The beam is typically focused by sending it through a microscope objective. The narrowest point of the focused beam, known as the beam waist, contains a very strong electric field gradient. It turns out that dielectric particles are attracted along the gradient to the region of strongest electric field, which is the center of the beam. The laser light also tends to apply a force on particles in the beam along the direction of beam propagation. It is easy to understand why if one considers conservation of momentum. Photons that are absorbed or scattered by the tiny dielectric particle in its path impart momentum to the dielectric particle. This is known as the scattering force and results in the particle being displaced slightly downstream from the exact position of the beam waist, as seen in the figure.

Quote from: Emc2 on 06/09/2012 11:37:04Quote from: evan_au on 04/09/2012 12:17:51A slight clarification about the difference between Mass and Rest Mass:The photon, traveling at the speed of light does have mass,and is deflected by a gravitational well like the Sun photons do not have any "mass' massA measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies. a Photon does not affect other particles gravitationally, cause it has zero mass....No, photons do not have mass, but they do have momentum. The proper, general equation to use is E2 = m2c4 + p2c2 So in the case of a photon, m=0 so E = pc or p = E/c. On the other hand, for a particle with mass m at rest (i.e., p = 0), you get back the famous E = mc2. ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN ( the goddard space centers site )massA measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies.

Quote from: evan_au on 04/09/2012 12:17:51A slight clarification about the difference between Mass and Rest Mass:The photon, traveling at the speed of light does have mass,and is deflected by a gravitational well like the Sun photons do not have any "mass' massA measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies. a Photon does not affect other particles gravitationally, cause it has zero mass....No, photons do not have mass, but they do have momentum. The proper, general equation to use is E2 = m2c4 + p2c2 So in the case of a photon, m=0 so E = pc or p = E/c. On the other hand, for a particle with mass m at rest (i.e., p = 0), you get back the famous E = mc2. ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN ( the goddard space centers site )massA measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies.

a Photon does not affect other particles gravitationally, cause it has zero mass....... photons do not have mass, but they do have momentum.

A clarification, please Emc2:Quotea Photon does not affect other particles gravitationally, cause it has zero mass....... photons do not have mass, but they do have momentum....sorry, you cannot view external links. To see them, please REGISTER or LOGIN ( content from link next )We also knew that photons are affected by gravitational fields not because photons have mass, but because gravitational fields (in particular, strong gravitational fields) change the shape of space-time In 1915 Albert Einstein proposed the theory of general relativity. General relativity explained, in a consistent way, how gravity affects light. We now knew that while photons have no mass, they do possess momentum (so your statement about light not affecting matter is incorrect). We also knew that photons are affected by gravitational fields not because photons have mass, but because gravitational fields (in particular, strong gravitational fields) change the shape of space-time. The photons are responding to the curvature in space-time, not directly to the gravitational field. Space-time is the four-dimensional "space" we live in -- there are 3 spatial dimensions (think of X,Y, and Z) and one time dimension.Let us relate this to light traveling near a star. The strong gravitational field of the star changes the paths of light rays in space-time from what they would have been had the star not been present. Specifically, the path of the light is bent slightly inward toward the surface of the star. We see this effect all the time when we observe distant stars in our Universe. As a star contracts, the gravitational field at its surface gets stronger, thus bending the light more. This makes it more and more difficult for light from the star to escape, thus it appears to us that the star is dimmer. Eventually, if the star shrinks to a certain critical radius, the gravitational field at the surface becomes so strong that the path of the light is bent so severely inward so that it returns to the star itself. The light can no longer escape. According to the theory of relativity, nothing can travel faster than light. Thus, if light cannot escape, neither can anything else. Everything is dragged back by the gravitational field. We call the region of space for which this condition is true a "black hole" (a term first coined by American scientist John Wheeler in 1969).Now, being scientists, we do not just accept theories like general relativity or conclusions like photons have no mass. We constantly test them, trying to definitively prove or disprove. So far, general relativity has withstood every test. And try as we might, we can measure no mass for the photon. We can just put upper limits on what mass it can have. These upper limits are determined by the sensitivity of the experiment we are using to try to "weigh the photon". The last number I saw was that a photon, if it has any mass at all, must be less than 4 x 10-48 grams. For comparison, the electron has a mass of 9 x 10-28 grams.

Surely this equation could be rewritten E = mc^2 + pc. Unless these are not exponential functions.

Light has been slowed and observed.http://en.wikipedia.org/wiki/Slow_light [nofollow]The question is why light travels at c in the first place. I can see the point particle principle but if mass increases as we reach light speed then why is the photon not massive? Maybe it is but because of it's other properties this mass can not be detected.

Quote from: hubble_bubble on 04/09/2012 16:06:00Light has been slowed and observed....sorry, you cannot view external links. To see them, please REGISTER or LOGINThe question is why light travels at c in the first place. I can see the point particle principle but if mass increases as we reach light speed then why is the photon not massive? Maybe it is but because of it's other properties this mass can not be detected.This (green text). Interesting question, I still no have a clue in that point.Also, how can 'born' a photon without any mass @ 300.000 km/s and without any acceleration as well?

Light has been slowed and observed....sorry, you cannot view external links. To see them, please REGISTER or LOGINThe question is why light travels at c in the first place. I can see the point particle principle but if mass increases as we reach light speed then why is the photon not massive? Maybe it is but because of it's other properties this mass can not be detected.

a photon is basically pure energy, that it why it can go from particle to wave and visa versa..

Quote from: Emc2 on 10/09/2012 09:51:33 a photon is basically pure energy, that it why it can go from particle to wave and visa versa..(red text) Hi, can you provide an example?

Quote from: hubble_bubble on 07/09/2012 03:08:23Surely this equation could be rewritten E = mc^2 + pc. Unless these are not exponential functions.Then, the equation 5^2 = 4^2 + 3^2 could be rewritten as 5 = 4 + 3?

Does anyone know of any work comparing time dilation and length contraction whilst leaving a gravitational field to those approaching light speed?

A pretty nice question that one, and yes, they differ. If we imagine Earth as 'moving' at one gravity, the time dilation expressed by that 'gravity' will differ from that of a spaceship moving at a constant one gravity, the faster it moves relative, for example. lights blue shift (measured locally in that frame), or Earth. The equivalence found with gravity is in its 'intrinsic properties' expressed, using a constant uniform acceleration, not about 'time'. And the same goes for length contractions.

Also a photon does not always theoretically travel at c. It is assumed that light cannot escape an event horizon.