What is light?

[j_rankin]

You are wrong about this. Light travels at a constant speed in a vacuum along the path of spacetime.

Thank you for landing us :lol:

I think I understand, but that has made me speculate.

If light travels at the same speed regardless of spacetime, then that could mean that the universe is decelerating.

I'll explain:

Perhaps the overall rate of time is completely dependent on the rate of expansion of the universe.

If space and time are inter-connected and light travels at the same velocity unaffected, then as the expanding universe actually slowed down, distant objects would appear to get faster when in fact it is us who are getting slower, and thus the universe is not accelerating but time is going slower.

 

[csmyth3025]

by j_rankin » Sun Aug 23, 2009 6:14 pm

Perhaps the overall rate of time is completely dependent on the rate of expansion of the universe.

I was wondering about that myself, only the other way around. In the early universe everything was a lot closer together. This implies, to me, that the strength of the gravitational field (everywhere) would have been a lot stronger than it is today. As I understand it, time slows down in a stronger gravitational field [from General Relativity Theory]. If this is the case, I'm thinking that our time is actually "faster" than the time of the early universe.

Of course this could all be "voodoo science" for all I know. I'm hoping someone with some expertise in such things can comment on our conjectures.

Chris

 

[darkmatter4brains]

by j_rankin » Sun Aug 23, 2009 6:14 pm

Perhaps the overall rate of time is completely dependent on the rate of expansion of the universe.

I was wondering about that myself, only the other way around. In the early universe everything was a lot closer together. This implies, to me, that the strength of the gravitational field (everywhere) would have been a lot stronger than it is today. As I understand it, time slows down in a stronger gravitational field [from General Relativity Theory]. If this is the case, I'm thinking that our time is actually "faster" than the time of the early universe.

Of course this could all be "voodoo science" for all I know. I'm hoping someone with some expertise in such things can comment on our conjectures.

Chris

This is gonna be voodoo science coming from me too, but the time dilation effect really needs a lot of mass around to become significant. The Earth itself doesn't even really have that much of an effect. The corrections on our GPS satellites to account for the fact that time moves at a faster rate in their orbit than on the surface of the earth, are pretty darn small. (Albeit they do propogate into rather large position errors if left uncorrected!)

Somebody correct me if I'm wrong, but I think the Inflationary model of the Big Bang is still the leading model and this has the Universe spreading out VERY, VERY fast early on. In fact, it has the Universe spreading out beyond our visible horizon. In other words, the Universe could be much bigger than we could ever see! Thus, in the early Universe the mass got "spread out" pretty quickly. If there as an era with overall slower time (relative to today) due to concentrated mass, it could have been a very short one.

 

[csmyth3025]

This may not be the correct thread, but I'm wondering if someone has calculated the Swarzschild radius for the event horizon of all the matter (visible and dark) and energy (known and dark) currently estimated to be in the universe. This is, of course, theoretical since - by definition of the problem - there wouldn't be anyone outside the event horizon to appreciate how big it is. Still, the first moments of the Big Band are described as starting from a point of (almost) infinite density and temperature. That sounds a whole lot like a singularity to me.

Chris

 

[MeteorWayne]

"Still, the first moments of the Big Band "

Actually, the Big Band era was from the late 1920's to the early 1950's

 

[BrankoRBabic]

What wonderfully educational exchange!
Can two or more photons link together to form one long photon of light?

 

[MeteorWayne]

What wonderfully educational exchange!
Can two or more photons link together to form one long photon of light?

NO

 

[csmyth3025]

"Still, the first moments of the Big Band "

Actually, the Big Band era was from the late 1920's to the early 1950's

The Big Band was my bag. I sometimes get my "g's" and "d's" mixed up

Chris

 

[BrankoRBabic]

Thanks Meteor Wayne but if two or more photons of light cannot merge to form one larger photon of energy, why NOT?

Does the same apply to all photons of energy such as gamma rays for example.

A fascinating experiment where an electron and a positron in reactive proximity, annihilate all the mass contained in each entity to release two gamma rays that shoot off in opposite directions. Would this mean that photons of energy produce incompatible fields that repel each other or is there some other reason why electromagnetic energy will not interact.

The observation raises a very interesting possibility and that is, that the gamma ray released from the positron is fundamentally different and irreconcilable with the gamma photon liberated by the electron. Has anybody examined the way each of these gamma rays precesses?

 

[origin]

The observation raises a very interesting possibility and that is, that the gamma ray released from the positron is fundamentally different and irreconcilable with the gamma photon liberated by the electron. Has anybody examined the way each of these gamma rays precesses?

The number and direction of the gamma rays resulting from the anihilation have more to do with the conservation of momentum than the gama rays somehow being 'fundemantally different'.

 

[centsworth_II]

....if two or more photons of light cannot merge to form one larger photon of energy, why NOT?

I don't know how terms like "long" or "large" would apply, but...

Laser-photon merging in strong laser fields http://www.mpi-hd.mpg.de/keitel/dipiazza/
"In the collision of a high-energy proton and a laser field, the laser photons can merge into one single photon as a result of the quantum interaction between the laser field and the proton Coulomb field"

 

[csmyth3025]

by BrankoRBabic » Wed Sep 09, 2009 1:48 pm

Thanks Meteor Wayne but if two or more photons of light cannot merge to form one larger photon of energy, why NOT?

I can't provide a scientific explanation in answer to your question. I pretty sure there is one. From a purely non-scientific perspective I think we all have observed that if you take two flashlights and point them at each other, or point them at an object in the room, the resultant light may be brighter (more intense) but it wont be any bluer (higher frequency).

I'm tempted to say that photons simply don't interact with each other - but I can't cite any authoritative source for this claim. I do remember reading a Wikipedia article that made this assertion here:

http://en.wikipedia.org/wiki/Two-photon_physics

The article is in the context of photon-photon pair production. It also provides a link which is too technical for me to fully understand here:

http://www.hep.ucl.ac.uk/~opal/gammagam ... orial.html

The Wikipedia article describes a mechanism by which high energy photons - which can't interact with each other - can create fermion/anti-fermion pairs if one of the photons (of sufficient energy) momentarily fluctuates into a particle/anti-particle pair within the Plank limit. The other photon then crashes into the particle, the anti-particle, or both imparting a momentum which drives them away from each other - thus preventing their mutual fluctuation (annihilation?) back into the original high energy photon.

As I understand it, Quantum Theory allows for these kind of "quantum fluctuations" to occur within the limits of uncertainty.

I have no expertise in this area so I'm hoping someone will jump in and provide a more authoritative source for this information. My understanding on this may be entirely wrong.

Chris

 

[BrankoRBabic]

This non combining property of photons is really interesting and probably, absolutely fundamental to why energy can neither be created nor destroyed.

Suppose that photons of energy say light, have a construct that is a closed loop ie there is no beginning and no end to any given photon of energy but a linked and closed arrangement, a thermodynamically stable construct . Would there be a geometry to such an arrangement?

 

[csmyth3025]

This non combining property of photons is really interesting and probably, absolutely fundamental to why energy can neither be created nor destroyed.

Suppose that photons of energy say light, have a construct that is a closed loop ie there is no beginning and no end to any given photon of energy but a linked and closed arrangement, a thermodynamically stable construct . Would there be a geometry to such an arrangement?

Unfortunately, I don't know enough about it to answer your question. I believe, though, that for any possible arrangement of mass/energy that might be proposed, there must be a geometry of space and time that is consistent with that arrangement.

Chris

 

[ZenGalacticore]

It's a particle/wave.

Or, one theory that I really like:

Light is a vibration in the Fifth Physical Dimension that we interpret as visible radiation. (Or a vibration in the fourth physical dimension within, beyond or outside of the fourth dimension of Time.)

 

[csmyth3025]

It's a particle/wave.

Or, one theory that I really like:

Light is a vibration in the Fifth Physical Dimension that we interpret as visible radiation. (Or a vibration in the fourth physical dimension within, beyond or outside of the fourth dimension of Time.)

Whenever I read about proposed fifth, sixth, seventh, etc. dimensions I always feel like a Flatlander trying to understand what "up" and "down" is. For me, it's a very hard concept to grasp.

Chris

 

[MeteorWayne]

Indeed.

And to previous posters, just saying it's from the fifth, fourth, or 8th dimension is worthless speculation unless there's a serious mathematically rigorous theory to back it up.

"I think" is not physics without support.

The plural of "I think" is not "A theory"

 

[ZenGalacticore]

Then it's a fascinating speculation. And tied in with so-called "String theory".

 

[BrankoRBabic]

Thanks “origin”
but that does not make sense. If it was simply a question of maintaining momentum then we would observe a random trajectory to the gamma rays but that is NOT the case. Always, the gamma rays escape by following a direction directly opposite to the other gamma ray, suggesting that there is some kind of repulsion and that can only be because the fields the photons generate, repel each other?

 

[BrankoRBabic]

Thanks ZenGalacticore
but the "space perturbation " identified with a photon of energy, must be caused by something. What is the nature of the causative agent?

 

[origin]

Thanks “origin”
but that does not make sense. If it was simply a question of maintaining momentum then we would observe a random trajectory to the gamma rays but that is NOT the case. Always, the gamma rays escape by following a direction directly opposite to the other gamma ray, suggesting that there is some kind of repulsion and that can only be because the fields the photons generate, repel each other?

1. Since there is a conservation of momentum of the system there would not be a random trajectory of the gama rays.
2. The annihilation events DO NOT always result in 2 gamma rays that move away from each other in exaclty opposit directions.
3. 3 or more gamma rays can be produced from an annihilation event.
4. The deviation from 180 degrees for 2 gamma rays that result from an annihilation evet is dependant on the intial momentum at the time of annihilation. Look at this experiment.

 

[andrew_t1000]

Light is electromagnetic radiation, the result of a magnetic field at right angles to an electric field.
That was how I thought a tuned L/C tank circuit in a radio transmitter worked.
Visible light is just really high frequency "radio" waves, isn't it?
And then beyond the visible spectrum it's higher frequency/energy.
To produce X-rays you need to hit a target with an electron beam at 45 degrees.
I get where the electric field is, but where is the magnetic field?

The same with visible light from a non thermal source like an LED or laser.
I understand the concept of pushing an electron out to a higher "orbit", then when it falls back it emits a photon.
So is the magnetic field coming from the orbiting electron?
Put another way, a magnetic field in a wire is created by current flow, so do atoms have a tiny magnetic field from all the electrons whizzing around the nucleus?

I'm not sure if I put that the right way, but I hope someone got it and can clarify it for me.

 

[BrankoRBabic]

Thank you very much origin, for the reference and the work done by Carl W Akerlof and Ann Arbor. This is the experimental evidence that one was hoping would be presented in a discussion taking place and is indeed the hoped for information.

The angular distribution resulting from the annihilation of the positron – electron, appears to be a relatively simple first order reaction that releases gamma rays that have a back to back trajectory, of 180 degrees to each other. The above work demonstrates a very minor deviation from a 180 retreat from the reactive site that is measured in milliradians ie fractions of a degree. This minor deflection would seem to me to be well within the energy limitations of the system to control the trajectory of highly energetic particles. It seems to me, that the deviation from the 180 trajectory is so minor as to be very much indicative of a direct effect of the two rays repelling each other.

If the trajectory of the gamma rays was indeed random then one would expect there to be examples of gamma rays moving in the same direction, in parallel or at right angles or at any other angle in the 3 dimensional space but that does not appear to be the case. Suggesting very much that there is a very powerful field repulsive force acting on the two gamma rays!

If there was no repulsion between the photons of energy we would observe energy “clouds” amongst other aggregations of energy . I would anticipate that the closer the photons approximate the greater the repulsive forces observed.

Has anyone detected the way photons precess and of particular interest would be the precessive properties of the gamma ray resulting from the electron and the gamma ray resulting from the positron, following the annihilation . One expects there to be a fundamental and irreconcilable difference in the two constructs.

Can one attach drawings with posts?

 

[csmyth3025]

by BrankoRBabic » Fri Sep 18, 2009 5:10 am

If there was no repulsion between the photons of energy we would observe energy “clouds” amongst other aggregations of energy . I would anticipate that the closer the photons approximate the greater the repulsive forces observed.

It's my understanding that photons (in their particle aspect) don't interact but electromagnetic radiation (in its wave-like aspect) can constructively reinforce or destructively interfere with itself in diffraction experiments such as the two-slit experiment.

As far as energy "clouds" are concerned, I don't recall coming across any references to such things. I suppose that a laser beam might be considered a "cloud" of energy, though.

Chris

 

[BrankoRBabic]

Thanks csmyth3025 and certainly any beam of energy can be considered as a cloud of photons eg switching a torch light on and off, will release directed photons into space as a cloud of photonic energy.

The concept of two gamma rays being repelled by a generated field is of considerable importance to the understanding of why photons do not interact to link up and form bigger photons. Clearly, this does not happen otherwise all photonic energy would have linked up by now but if fields are generated that repel photons from each other, why then is it that a laser light remains contained in a finite beam, all the way to the moon and back? Generated fields would disperse all photons within the beam soon after the beam was projected.