how can light attain light speed?

Question

okay its been ages since i did quantum physics so i may be totally wrong but isnt one of the thoeries that light is delivered in 'packets' and therefore has a mass (on the sub atomic level), so is in fact a particle acting as a wave? but if light has mass then according to einstein it could never attain light speed because its mass would become infinate? I could be totally wrong and if i am id appreciate someone simply telling me rather than saying "your so stupid, etc etc".. lol sorry it bugs me (i mean if i was a quantum physicist i wouldnt be asking would i?)

Answer 1

hey! I asked this a short while ago and here's what I got http://uk.answers.yahoo.com/question/index;_ylt=AoOcIfgCzwm3WOPBf0buPwogBgx.?qid=20060724160247AAWzHMX
Some good answers. Deal seems to be that light has relativistic mass when it's moving but no rest mass. If you have no rest mass, your mass doesn't become infinite when you reach light speed. The idea of light "at rest" is bollox of course but that doesn't matter, it's just a mathematical way to express what's going on.

Answer 2

Yes, No, not quite a finite!

Yes: it does travel in packets from the point of view of quantum.
Yes: it is a wave EM wave as well.
This is the wave-particle duality that caused arguments throughout early physics understanding, as the two opposing camps didn't realise its both.
Yes: Einstein would say a object that attain 'c' from rest would have exponetial mass increase.
No: light doesn't attain light speed it always is at 'c'

Now the not quite finite: photon particles have zero rest mass, (the instance of emmision or absorbtion they have no mass for no measurable amount of time), but do actualy have mommentum hence the solar-sail (I've seen a small solar mill in a vacum spin just because of the sun's rays) idea. So since they have zero rest mass by Einsteins relativity equations they still technically have zero mass (Don't worry about momentum=mass*verlocity it just gets silly).

Just to confuse issues more all objects bellow light speed will never reach it because the accelrative force reaches infinity as well, and any particles that travel faster will never go below. Yes some rare fundamental particles do go faster, but have zero rest mass.

Oh, as for packets, its about emmison and absorbtion energy level requirements... but this is a side issue...

Hope that's given more answers than questions!

Answer 3

There are two ways of looking at light: one is that it comes in particles called photons, with the energy of each photon proportional to the frequency of the the light; this is demonstrated by the photoelectic effect. Another is that light is a wave, demonstrated by it's ability to interefere and diffract. This may seem like two opposing view points but in the world of quantuam physics ideas of waves and particles becoming all mixed and confused.
As of the question of light having mass. According to einstiens theory, any object that starts off moving more slowly than the speed of light, it will become increasingly more difficult to make it move faster as it approaches light speed i.e it's inertial mass increases. It's mass would therefore tend to infinity as it's speed tends exponentially closer to light speed. However, according to the theory it is possible for a particle to move at the speed of light, if it has always been travelling at light speed. This overcomes the difficulty of infinite mass since it has always been moving at light speed and so hasn't needed to be "pushed" up to that speed.
I would say light does have mass by virtue of it's energy; but it's rest mass is zero meaning it can't stop and must forever move at c. I hope this helps. Maybe i'm more confused!
regards
Paul

Answer 4

Wave particle duality is a myth used to explain the peculiarities of electrons in particular (no pun intended) particles acting as waves, but has generalised to photons (all quanta actually) as well, in this case waves acting like particles.

Electromagnetic waves travel at the speed of light, that's it. When you are not looking very hard photons are waves and do the things that waves should do.

Then, when you start look harder, the more strangely these 'waves' seem to act. This is because, as Heisenberg pointed out, you cannot observe a phenomenon without altering that phenomenon. The mere act of observing causes the observed to change its behaviour.

The harder you hit a ball the further it goes, in the same way, the harder you look at a phenomenon, the further awry it goes until you appear to be looking at something quite different to what you started looking at, ie. a particle instead of a wave.

Of course as soon as you look away again it's just a wave behaving as a wave should.

Answer 5

It seems to be an incredibly common misconception that light has mass because it exhibits particle behaviour. This is because of the outdated and complex idea of "relativistic mass", using E=mc^2. However, the full version of the relativistic energy formula is
E^2=(mc^2)^2+(pc)^2
meaning massless particles to have energy in the form of momentum, and not mass. The m in the equation stands for rest mass and photons do not have such a thing, as they are never at rest. This, also, is why they don't accelerate to the speed of light - they are created travelling at that speed.

Answer 6

You are right that light is delivered in 'packets' but your error is in assuming that those packets (which we call photons) have any mass..

Photons have zero rest mass, and consequently do not acquire infinite mass when travelling at light speed. In fact photons always travel at the speed of light. The only reason that they appear to slow down when travelling through physical objects such as glass or water, is that the atoms of the substance they are passing through absorb and re-emit the photons, taking time to do so.

Answer 7

You got it wrong. The packets principe doesn´t mean that light has mass, just as energy doesn´t have mass but still is delivered in packets. The packets just assure that there is a lower possible number delivered at once, lower than that is not possible. Is a matter of how far one can zoom into universe. Therefore light has no mass.

Answer 8

The most famous paradox for any undergraduate physicist. In actual fact light is something which has momentum like a particle would, but no mass like a wave.

To further the debate, look up deBroglie's postulation which says that all particles, or chickens, or spaceships behave like a wave...

Answer 9

An experiment showed that light has a duel nature, it has the NATURE of a particle and the nature of a wave. Photons are discrete quanta of energy that have a wavelike and particle like nature. This is different to saying that they ARE a wave and are a particle. Hence no mass.

Answer 10

Very interesting Question !!!
Few questions exposes the stupid thoughts we are bound to think on ! (because today we have no logical answers)
Similarly Think " Who tells to two electrons to go away each other while they are quite distant apart"
Logical answer to this question is that - there is a medium which is made up of particles(very tiny), these particles are traveling randomly with velocity equal to light, any disturbance in the medium will obviously travel with velocity of Light. Some day this approach will strike back, it has to happen, remember my words !!!!!