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InfinateLoop
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I am hoping someone could let me know how far light can travel?
InfinateLoop said:Yes, very helpful thanks!
So on a quantum level is this a massive collision? A photon is traveling at c and comes to a screeching halt?
Sorry, I don't think that's right. EM fields most definitely carry momentum and can transfer it to massive particles. Invoking F=ma isn't quite appropriate since it describes the acceleration of a massive particle, which, as you've said, the photon is not. Better is to use F=dp/dt, i.e. a force produces a proportional change in momentum (which reduces to ma for a particle with constant non-zero mass).ok123jump said:If by "massive" you mean forceful, that is not what the evidence indicates. Conventional Quantum Mechanical Theory says that a photon has no mass. F=m*a implies that there cannot be a force at all - the interaction of an atom with a photon must be an event which is essentially force-less. This if it is true that a photon has no mass, this would allow photons to slip in and out of atoms without affecting the momentum. As far as we can tell experimentally, it appears that this is the case.
Adversarily, I must state that we cannot say for sure. The Quantum Theory of Optical Phenomena by J.C. Slater and David Bohm suggests that a photon has mass and may be treated mathematically similar to an electron. Although I tend to lean in my personal beliefs toward this theory, it is still contentiously debated.
If Slater and Bohm are correct, then a photon does have mass - if so, the absorption or emission of a photon would result in a slight change in momentum and mass. However, we have not been able to experimentally verify this suggestion.
In summary, it appears that because the photon is massless, the velocity does not truly matter because the momentum of the atom in question is not changed by the absorption/emission of a photon.
ok123jump said:If light (as in photons) were in a vacuum, it would travel forever in a given direction.
In reality however, it is far more probable that light will experience disturbances (absorption, reflection, refraction, etc..) as it moves through space - thus, it's distance of travel is limited to some finite distance. I do not think that there is any good estimation for this realistic finite distance. Clearly, this finite distance depends on the situation of the light being transmitted, direction and regions of space through which it will travel.
dgtech said:So then it is possible for the observable universe to be limited by distance rather than time?
dgtech said:you mean redshift?
Who gave you the idea SETI was looking for sound? That would be silly, since sound waves can't travel through space. SETI does look for light signals, mostly radio waves.thomas pesek said:was just wondering, in SETI, instead of searching for sound, wouldn't it be wiser to search for light ? wouldn't that travel farther and faster ?
From an alien planet's perspective, even a close one, Earth is nearly indistinguishable from the Sun. So any laser we build would have to outshine the sun, or we'd have to count on the aliens having much better telescopes than we do.thomas pesek said:I mean, why not send out messages ourselves, piggy backed on laser beams ?
if found, maybe they'll reply ?
dgtech said:It's not a practical question, perfect vacuum likely does not exist
However, even in perfect vacuum gravity will affect photons - a very weak effect but present, at least in the current model
dgtech said:It's not a practical question, perfect vacuum likely does not exist
TwistedMister said:...considering space is infinite,...
pallidin said:OK, unimpeded with respect to physical blocking atoms/objects.
What happens to that photon over VERY EXTENDED time? Decrease in wavelength?
jonpaulv said:But this would make time irrelevent. If you think about light years in distance, then that would mean I'm able to calculate 30000000000000 light years. And it only takes you a day to calculate the distance of a light source to you, yet that light source took that long to get to you. So how can we measure light in distance if traveling at that distance is observable in an instant. And if something does abosord the light in space then that proves the existence beyond the life span of light. Meaning if light stops because it is effected means that which effects it is there and more.
jonpaulv said:The energy level of the light is errelevent. If the light always weakens as it travels that means that light has life span. And distance from point a to point b is infinite no matter what travels through it. So there is no point a or point b unless something is moving toward it. So that start of some energy to the end of some energy is always equal. no matter its distance. It is only the time spent between the two points that is created by our mind.
rolls said:So over time some photons are going to "Escape" the universe, eg let's say the majority of matter is in a predefined area, and as you move further away from this area there is less and less material. If photons escape the material that means they will be moving further away from the "universe" and will never collide with another atom again.
Would this energy be effectively lost then because the photon will travel for ever and ever and never return?