Humans travelling at light speed?

[JDoolin]

what confuses me is that the "photon" doesn't experience time. so each photon of light is actually light from the very beginning of the Big Bang?

Well, if you want to make the case that the big bang produced atoms, which later became part of the sun, which released light. You could try to make the case that that light was "from" the big bang.

But for some period during that time, the energy from that photon was stored as potential energy, in the capacitive properties of a battery, or the distance between swirling particles in the formation of a star, as kinetic energy in the form of excited atoms (ions or electrons in upper valence shells), or as heat energy, in the form of extra velocity in the atoms, or as mass energy, in the form of binding energy in the nucleons.

The particles involved in that "energy storage" experienced time.

 

[mibaokula]

Well, if you want to make the case that the big bang produced atoms, which later became part of the sun, which released light. You could try to make the case that that light was "from" the big bang.

But for some period during that time, the energy from that photon was stored as potential energy in the form of excited atoms, or as heat energy, in the form of extra velocity in the atoms.

The particles involved in that "energy storage" experienced time.

i never thought about it like that. but still, energy in the form of photons does not experience time - though all surrounding the photon would appear to age at an infinite rate.

 

[mibaokula]

if you believe in string theory, and a photon is a string, how would the "string" experience the length compacting that objects traveling near to and at the speed of light experience.

 

[ghwellsjr]

surely the photons aren't destroyed but their wavelengths lengthened. i.e., visible light radiates on the black shirt and infra red is emitted? with the light-bulb, electricity in the circuit meets a very high resistance to the extent that visible light is radiates as the temperature reaches a critical level?

Photons always travel at c, by definition. The photons that come from a light bulb had no existence prior to their emmision when the light bulb gave up a packet of energy for each one and they end their existence when they hit something and that same exact amount of energy is absorbed by the target. It's possible for the target to re-emit a different photon some time later at a different wavelength and with a different amount of energy, but that is a new photon that may have gotten its energy from parts of many different photons.

 

[mibaokula]

Photons always travel at c, by definition. The photons that come from a light bulb had no existence prior to their emmision when the light bulb gave up a packet of energy for each one and they end their existence when they hit something and that same exact amount of energy is absorbed by the target. It's possible for the target to re-emit a different photon some time later at a different wavelength and with a different amount of energy, but that is a new photon that may have gotten its energy from parts of many different photons.

so energy cannot be created or destroyed but particles can?

 

[JDoolin]

if you believe in string theory, and a photon is a string, how would the "string" experience the length compacting that objects traveling near to and at the speed of light experience.

For me to believe in something, I have to either be able to experience it, visualize it, or understand it.

If I believed in string theory, I would be doing so without any comprehension of what I believed in. Let's calll me "string theory agnostic," since I've never heard any description of it that made any sense to me, or of any evidence to support it.

I'm much closer to believing in "deBroglie matter waves," but frankly, I don't really understand them, either.

https://www.physicsforums.com/showthread.php?t=458792 (Edit: The paper in post 10 really looks like it would be worth spending a few days working through.)

Using deBroglie waves you might (or might not) be able to make the case that all the mass-energy was somehow a superposition of waves moving at the speed of light.

But regardless of whether that's true or not, the end effect of all that are bodies that have mass, and experience time.

 

[JDoolin]

so energy cannot be created or destroyed but particles can?

Right.

 

[nitsuj]

surely the photons aren't destroyed but their wavelengths lengthened. i.e., visible light radiates on the black shirt and infra red is emitted? with the light-bulb, electricity in the circuit meets a very high resistance to the extent that visible light is radiates as the temperature reaches a critical level?

I understand it to be the energy of the photon is converted mostly to heat energy (infra-red?) I understood the photon to be a description of visible light in this context, which there would be essentially none reflected off the black shirt.

The atoms in the light bulb filament get hot. The electrons radiate the excess energy as brand new photons.

I think the difference in interpretation here is you are using a correct definition for a photon, a "packet" of pure electro-magnetic energy. I am using it to describe visible light.

 

[bernsten69]

I believe that the problem you are having 'imagining' what it would be like to be a photon is as follows:

There is a huge (literally infinite) difference between what an observer would observe as its speed approaches the speed of light versus what an 'observer' would observe while traveling AT the speed of light.

Time dilation, space contraction etc. are all effects of having a velocity less than C with respect to another frame of reference.

Rather than calculating the limit as V -> C, if you set V = C, you end up dividing by Zero, which, rather than giving us infinity (which is the limit as you approach C of 1/SQRT(1-v^2/c^2)), gives us a non-answer. Dividing by zero is a non-mathematical process that has no calculable result.

Therefore, if you ask the question, what does a person traveling at the speed of light observe, I believe the answer is non-calculable (probably because it is impossible) (and there is no reason to believe that it has anything to do with time-dilation or space contraction).

If you ask the question, what does a person accelerating towards the speed of light observe, the answer would be that, as you approached the speed of light, infinite time (and space contraction) with respect to the rest frame would pass(occur).

However, your question is neither of these two. Your question is what does light 'observe'. Light cannot 'observe' anything for a number of reasons, but here is a good one: there is no inertial frame of reference for 'light.' To observe something, you must interact with it in some manner. To interact with something, it must be able to be described in your frame of reference in some manner. From our frame of reference, we can see light interacting with matter and other electromagnetic waves. However, there is no known transformation from our frame of reference to 'light's' (non-existent) frame of reference. Attempting to perform this 'transformation' by imagining acceleration towards the speed of light, or even matter traveling AT the speed of light is improper. However, this is what you are attempting to do.

Here's another example why it doesn't make sense to try to imagine what light observes:

Among the often ignored solutions to Maxwell's equations are Advanced Waves which travel backwards in time. Attempting to imagine what a photon observes (travelling forward in time) makes just about as much sense as attempting to imagine what a photon observes traveling backwards in time. It would appear (from our reference frame), that the assumptions we typically make (ie, time progresses forward), may not apply to light.

Here's a better analogy: Attempting to determine what 'light' observes is akin to attempting to determine what the x-axis observes. Although it may have a value (ie, at position 5 for the x-axis) (or for light, a wavelength and direction of propagation), it does not 'observe' anything. There may be a formula that describes what value the X axis has at some point (just as those that describe the attributes of light), but that does not mean that it can 'observe' anything.

In some ways, space-time, matter and energy are all the same thing, but light has no mass and a constant velocity with respect to all reference frames. Therefore, attempting to ascribe a reference frame to it makes no sense.

 

[ghwellsjr]

Photons always travel at c, by definition. The photons that come from a light bulb had no existence prior to their emmision when the light bulb gave up a packet of energy for each one and they end their existence when they hit something and that same exact amount of energy is absorbed by the target. It's possible for the target to re-emit a different photon some time later at a different wavelength and with a different amount of energy, but that is a new photon that may have gotten its energy from parts of many different photons.

so energy cannot be created or destroyed but particles can?

If you have the right equipment, you can create particles with mass from energy or you can use some or all of the mass of particles to create energy. For example, it is possible to create an electron and a positron from pure energy. These two particles have the same mass the only difference being that the positron has a positive charge on it. However, the positron will soon be attracted to an electron (maybe the same one that was earlier created with it or a different one, it doesn't matter) and the two will annihilate each other giving up all the energy that was originally use to create them. This is an extreme example to show the conversion between mass and energy but there are many other examples where this is happening all the time. Whenever an atom or molecule emits a photon, it loses some mass. Whenever an atom or molecule absorbs a photon, its mass increases.

 

[mibaokula]

If you have the right equipment, you can create particles with mass from energy or you can use some or all of the mass of particles to create energy. For example, it is possible to create an electron and a positron from pure energy. These two particles have the same mass the only difference being that the positron has a positive charge on it. However, the positron will soon be attracted to an electron (maybe the same one that was earlier created with it or a different one, it doesn't matter) and the two will annihilate each other giving up all the energy that was originally use to create them. This is an extreme example to show the conversion between mass and energy but there are many other examples where this is happening all the time. Whenever an atom or molecule emits a photon, it loses some mass. Whenever an atom or molecule absorbs a photon, its mass increases.

in other words, energy is not created or destroyed etc. if there is net no energy, there must be a particle of positive energy and then a particle with negative energy to balance out (perhaps not the best example).
if you believe in the big bang (the universe came from nothing), why have we not been annihilated yet?

 

[ghwellsjr]

in other words, energy is not created or destroyed etc. if there is net no energy, there must be a particle of positive energy and then a particle with negative energy to balance out (perhaps not the best example).
if you believe in the big bang (the universe came from nothing), why have we not been annihilated yet?

I hope you're not thinking that my example of creating a pair of massive particles worked because one of them had positive energy and one of them had negative energy, no, they both have exactly the same positive energy.

You should ask your question about the big bang on another forum.

 

[mibaokula]

I hope you're not thinking that my example of creating a pair of massive particles worked because one of them had positive energy and one of them had negative energy, no, they both have exactly the same positive energy.

You should ask your question about the big bang on another forum.

yeah, forget about that. I'm digressing from the original question
if two bodies are moving at 99.9999999999999999999% the speed of light (hence they fit into Einstein's idea of reference frames and have inertia/mass) in the opposite direction, what happens

and someone said that light can only travel at the speed of light in any reference frame; what about refraction when light is slower in a denser medium

 

[bernsten69]

yeah, forget about that. I'm digressing from the original question
if two bodies are moving at 99.9999999999999999999% the speed of light (hence they fit into Einstein's idea of reference frames and have inertia/mass) in the opposite direction, what happens

and someone said that light can only travel at the speed of light in any reference frame; what about refraction when light is slower in a denser medium

There is a problem with your first statement that Special Relativity explains. Two bodies cannot be moving away from each other, each at 99.9999999999999999999% the speed of light. If this were possible, then light from one person shot at the other would never reach him. The speed of 'recess' between these two bodies is not the SUM of the speeds that they are traveling at with respect to a fixed reference frame (their origin/earth for example). If they both left from Earth going away in opposite directions at 99.9999999999999999999% the speed of light, if you were standing on earth, you would see each individual speeding away at exactly that speed (calculable from their doppler shifts). However, when you CHANGE your reference frame from that of Earth to that of one of the travelers, Special Relativity has a specific transformation that must be applied to what you see when you look at the other person's speed (via their doppler shift) (they do not add in the classical sense).

See http://www.desy.de/user/projects/Physics/Relativity/SR/velocity.html for a simple explanation and formula to answer your question.

If you ask WHY this happens, mathematically, it follows from the assumption that the speed of light is constant in Any reference frame. If you look up the derivation of Special Relativity, you will see how it follows from that base assumption.

The Speed of light is constant in any reference frame. In a dense medium, the speed of light is locally slowed, but the reference frame invarient remains the same. If you want to discuss what happens at the quantum level to 'slow' light, I am about 10 years behind in QFT (etc.), so someone else can better explain that effect. (I've since switched fields). However, slowing light with quantum effects does not change any of the effects of special relativity (as far as I recall).