Photon question

Thinking about light waves and photons here and I came up with a question I can't answer. We see light from stars that are millions of light years away, but how exactly does it get here? What is the shelf life of a photon? These tiny particles that emit light for millions of years? So tiny yet they seem to have an unending energy source how do they do that? Traveling through the cold recesses of space you would think they would freeze or some how their energy would be drained. Do they emit heat also, I am under the impression that anything that gives off light also gives off heat, unless heat is only given of when something absorbs a photon, but that would still be a conversion of energy so that means the photon would have to have energy to begin with. How does it store this energy for millions and millions of years? For something so tiny you would think the answer to this would be simple and uncomplicated.

A phtono is a particle of light. It does not give off light, nor does it give off heat.

It moves in a strait line through space until it hits something, like your eye, or a planet, or so on. Also starts give off a LOT of photons so plenty can make it to us without bumping into something.

Photons are massless particles that move at (drum roll please) the speed of light. They can even pass trough some materials, such as glass, most gasses, and so on.

It does not take energy to move in a strait line through space. Basic momentum laws show that it only takes energy to accelerate things, i.e. slow down or speed up. Staying at teh same speed take 0 energy.

Hope this helps.

Originally posted by Quest
It does not take energy to move in a strait line through space. Basic momentum laws show that it only takes energy to accelerate things, i.e. slow down or speed up. Staying at teh same speed take 0 energy.
Hope this helps.

But what got the photon to the speed of light? Fussion? Fission? The energy output would depend on how far it went right? Or would it continue forever? A flashlight would produce a photon correct? But it doesn't go forever...or is it simply fading into a different light spectrum when we no longer see the light?

Originally posted by NetStorm
But what got the photon to the speed of light? Fussion? Fission? The energy output would depend on how far it went right? Or would it continue forever? A flashlight would produce a photon correct? But it doesn't go forever...or is it simply fading into a different light spectrum when we no longer see the light?

Heh...you'll probably not like this answer, but nothing got it moving that fast. its light, thats just how fast it moves. Hense the speed of light being the only constant speed in the universe.

If you were moving at 90% the speed of light in the same direction as a photon and measured the speed of that photon it woudl still be going the speed of light! (not 10% the speed of light).

Such is our strange universe.

Since a photon has ZERO mass, it take ZERO energy to accelerate it. Only when a phton is pasing through clear matter (like the atmosphere) does it slow down, and even then its only because it moves through clear things by passing into and out of electrons...the speed is then limited by how fast electron can quantum tunnel through energy states to pass it along.

Yes. I would just like to add that photons are light, and as such, they don't emit light. Light emitted from other elements generally happens because of a change in the state of an electron, from one level to another. This causes photons to be released, at the speed of light. (186,282 miles/sec)

Interesting, no?

Since a photon has ZERO mass......

Quest , a quick tutorial on lasers if you could . I always thought photons had immesurably small mass , and have seen that flying pan thingy that is launched with pulsed lasers .

hmmm, interesting. What does it mean to be a particle of light? Also saying that light always moves at the speed of light is like saying a car always moves at the speed of a car? Photons have to have mass, if they didn't than they would not get caught in black holes, they would pass right by.

Too true. Light, and therefore photons, are affected by gravity, and I do believe that they possess some miniscule mass. Scientists have recently slowed light down to 27 miles/sec (I think. Regardless of the actual speed that they managed to slow it to, it was a walking pace compared to the standard accepted speed of light at 186,282 miles/sec. There are also theorists that state that the speed of light isn't necessarily a constant, and that Einstein was wrong on that point. See this article.)

Light can't have mass, because then it would have infinite energy because it moves at the speed of light. It does have momentum.

Originally posted by amantine
Light can't have mass, because then it would have infinite energy because it moves at the speed of light. It does have momentum.

That doesn't answer what I said. an object with no mass would not be effected by a black hole. But light is pulled into black holes, so unless you can explain how something without mass is effected by gravity I will say you are wrong.

Photons have zero mass, that's why they move at the speed of light. The reason they are affected by gravity - a black hole is just an extreme example - is not that they are directly attracted (zero mass, remember, so no mutual attraction) but rather that gravity deforms spacetime, thereby changing the path that the photon takes. For black holes, the gravity well is so steep that the light which falls inside the event horizon continues on it's journey for an infinite period of time.

To borrow the car analogy, it's not that the bottom of the hill is attracting the car, it's that the bottom of the hill changes the geometry of spacetime so the car is heading toward it.

I know it sounds a little counterintuitive, but I hope these links help:

imagine.gsfc.nasa.gov...
fdonea.tripod.com...

And especially...

www.astro.ku.dk...

Originally posted by J0HNSmith
hmmm, interesting. What does it mean to be a particle of light? Also saying that light always moves at the speed of light is like saying a car always moves at the speed of a car? Photons have to have mass, if they didn't than they would not get caught in black holes, they would pass right by.

Light moves at the speed of light. No matter what your frame of reference light moves at about 300000000 meters per second.

Photons have no mass, as has been said they are sucked into black holes because SPACE is sucked into them.

There are other particles without mass as well. Such as the graviton. They all move at the speed of light.

A quick note - c is the speed of light in vacuum. It takes longer to travel through a medium such as water, hence why a straw appears to bend at the air-water interface. An interesting bit of trivia regarding this is that if you were to follow the path of a photon through air and water, it will always be the optimum time-of-flight path.

[edit on 6/16/2004 by PurdueNuc]

they also act like waves, that might help explain some.

Originally posted by J0HNSmith
That doesn't answer what I said. an object with no mass would not be effected by a black hole. But light is pulled into black holes, so unless you can explain how something without mass is effected by gravity I will say you are wrong.

Why does something have to have mass to be affected by gravity? Light or any other particle just follows its geodesic, mass or no mass. A simpler explanation is that light takes the straightest possible line through curved spacetime and that we percieve this as light being attracted by mass. It doesn't matter if you have mass or not to follow the straightest possible line.

A more complicated explanation is that for light in vaccuum the rule that the covariant derivative of the velocity 4-vector along itself is zero. Mass is not included in this formula.

I do some work with high power lasers and I still think photons have the smallest mass possible. Unless you can explain why a hovering cork with a super conductor setup underneath it spins when a CW 1064nM yag beam is aimed at its side, or a ping pong ball is moved and no vapourization occurs.

Does light bend into a black hole or does it swirl in? Also, if you were going 99.99% of C, I think relativity still applies, unless photos have some NO2 hidden somewhere.

From my understanding of a photon;
They are particles of light, more precisely, electro-magnetic waves, in the same way that a radio-wave is an electromagnetic wave.
If you consider a light source to be a gun, then the light would be the bullets coming out from it. They travel at the speed of light when in a vacuum, and have no mass. They are only influenced by gravity because space-time paths are distorted around the gravity 'wells' of a place, and as such, their path is still 'straight', but goes through a 'dent' as such.. Imagine rolling a ball around a trampoline with a 'dent' in the middle, that is the same effect.
I hope this helps

OK...

A photon when emitted by somthing, if its in a vacuum for example, will go at c (something like 300 thousand kp/s) BECAUSE it requires energy to move something with MOMENTUM (which is mv *mass x velocity - but sicne it doesnt have ANY mass its momentum = 0 so it therefore takes ZERO engergy to accelerate it to the speed of light *which is virtually instananeous anyway).

EDIT:
Photons DO have momentum (because E=mc2) since they have energy. (otherwise we wouldnt be able to work out their wavelength!)
But then how can they travel at th speed of light? Am i missing something here?


The theory of relativity says that spacetime can be warped by matter AND energy and that space time can warp them, so a photon which still has ENERGY is affected by gravity (in your case a black hole)

Light doesn't give off heat nor does it carry any heat at all ( i dont no if this is true - except for infra red radiation??)

Basically we can see the stars still because they pump out so many photons that it doesnt matter. Only a fraction will get lost to gravity, dust clouds, planets, asteroid belts etc.

And no, you cant see light unless it enters your eye, thats why u cant see a laser.but u can see the dot or wateva it makes because its reflecting into your eye.

EDIT: Does gravity only accelerate things with mass? IT does rite? Because thats why light doesnt go faster when being sucked into a gravity well rite? Unlike a ball dropping from a plane?


[edit on 17-6-2004 by quiksilver]

Can a photon really be called a particle if it has no mass? I always thought a photon was the smallest measurable energy exchange between sub-atomic particles, and therefore a 'quanta' of energy - a unit of measurement like a metre or second - not a 'particle' as a lot of people call it. Can someone clear this up for me?

Yes it is a particle.

Many definitions thou

1.In "particle physics", a subatomic object with definite mass and charge.
2.One of the minute subdivisions of matter, as an atom or molecule.
3.A finite mass with zero dimensions, located at a single point in space
4.A piece or small bit of matter.
Some apply some dont to light, but its generally thought of as a particle(BUT ALSO AS A WAVE **wave-particle duality)
(remember E=mc2) is energy/light classified as matter?