[Emc2]

  a photon is basically pure energy, that it why it can go from particle to wave and visa versa..

(red text) Hi, can you provide an example?

http://en.wikipedia.org/wiki/Double-slit_experiment
This result establishes the principle known as wave–particle duality. Additionally, the detection of individual photons is observed to be inherently probabilistic, which is inexplicable using classical mechanics.[3]

[yor_on]

There might be one way more too look at it?

'Gravity' is the metric of Space defining it. I become flabbergasted trying to imagining all those 'geodesics', paths of smallest or no 'resistance that becomes the easiest choice for all uniformly moving things. To see the point here you have to imagine all those objects, all able to 'distort' space and all moving relative each other, in different directions simultaneously. It must be very dynamically balanced system SpaceTime. And the photon is just one of those 'objects moving'. What they all comes down too, from the photon to matter, is that they all can be tracked back to 'energy'. So the geodesics gives 'energy' the paths, and they all must change with relative position, simultaneously for all involved. The alternative, as we never see a photon 'move', only when it 'comes to be' as in the recoil from the system it 'leaves' and in its annihilation, is to assume some logic allowing those two to exist without it needing for anything to be there in between. But if so, it still behaves exactly as all other 'moving objects.

Anyway, photons-matter, expressions of 'energy'.

[hubble_bubble (OP)]

It is interesting to note that at the Planck scale, if we consider 1 Planck length to be an absolute, that light travels this discrete distance in 1 Planck time. If we don't worry about the macroscopic scale this all makes sense. Consider a shrunken universe contained within say 10 cubic planck lengths. Each cube will contain shrunken particles, of which only photons can jump to the next cube instantaneously. Every other particle is trapped in a particular cube until its momentum moves it to an edge. In this scenario all particles within each cube will see light at the same speed. To move faster necessarily contracts the distance traveled due to dilation. The distance is experienced as less from an external observer.

If a photon starts 10 cubes away, it will reach each cube within a set interval and all particles within a particular cube will 'experience' it at the same instant. This can be scaled up and still works. So it doesn't matter if we measure in Planck scale or metres.

What if the length contraction also applies to the photon moving through this frame? As if spacetime in and around a moving object does contract physically. This could relate the effects of momentum to those of gravity. Ultimately a black hole contracts all spacetime into a singularity (theoretically).

[hubble_bubble (OP)]

Does anyone know of any work comparing time dilation and length contraction whilst leaving a gravitational field to those approaching light speed?

[hubble_bubble (OP)]

Surely this equation could be rewritten E = mc^2 + pc. Unless these are not exponential functions.

Then, the equation 5^2 = 4^2 + 3^2 could be rewritten as 5 = 4 + 3?

Yes sorry I had my stupid head on.

[imatfaal]

EMC2 assertions concerning the claim that the photon is pure energy have been moved to New Theories

http://www.thenakedscientists.com/forum/index.php?topic=45584.0

[imatfaal]

Does anyone know of any work comparing time dilation and length contraction whilst leaving a gravitational field to those approaching light speed?

Sorry HB - just seen this question.  Firstly - I am pretty sure that you only get length contraction in high relative velocity cases.  Secondly - I guess you are looking for qualitative differences between the time dilation caused in the two different circumstances; I just don't know.  Frankly I cannot think how time a/o time dilation could be different (aprt from quantitatively).  And I do know that you can add the two effects to get a single result - this is done all the time in the GPS satellites; high speed makes the clocks slower, and higher grav potential makes the clocks tick faster, but you can just add the two effects and get the actual correction. 

At present I cannot imagine how there would be two types of effect (rather than two causes) and in the one case I know of where they both apply they are simply added - so I would guess there is no difference.

[yor_on]

A pretty nice question that one, and yes, they differ. If we imagine Earth as 'moving' at one gravity, the time dilation expressed by that 'gravity' will differ from that of a spaceship moving at a constant one gravity, the faster it moves relative, for example. lights blue shift (measured locally in that frame), or Earth. The equivalence found with gravity is in its 'intrinsic properties' expressed, using a constant uniform acceleration, not about 'time'. And the same goes for length contractions.

[hubble_bubble (OP)]

A pretty nice question that one, and yes, they differ. If we imagine Earth as 'moving' at one gravity, the time dilation expressed by that 'gravity' will differ from that of a spaceship moving at a constant one gravity, the faster it moves relative, for example. lights blue shift (measured locally in that frame), or Earth. The equivalence found with gravity is in its 'intrinsic properties' expressed, using a constant uniform acceleration, not about 'time'. And the same goes for length contractions.

Also a photon does not always theoretically travel at c. It is assumed that light cannot escape an event horizon. Can this be still considered a vacuum? If not then what is inside the event horizon may not be a singularity. As we know light travels slower through a medium. Does this imply that intense gravity acts like a physical medium?

[lightarrow]

Also a photon does not always theoretically travel at c. It is assumed that light cannot escape an event horizon.

It doesn't matter if it can't escape: light in the void always travels at c by definition.

[JP]

hubble_bubble, a photon does always travel at c in a vacuum, by definition.  In general relativity, this means with respect to the patch of space immediately around the photon.  It's a bit like running on a treadmill.  If you run at a constant speed with respect to the conveyor belt under your feet and someone slowly turns the speed up, you'll move at different speeds with respect to someone who's not on the treadmill.  You'll eventually start going backwards even though you're gong a constant speed with respect to the belt beneath your feet. 

This happens because light always moves at c over regions of flat space-time.  Gravity makes space-time curved, but over any tiny portion of a curve, it looks flat (much like the earth's surface looks flat to us even though it's not).  So over a very small neighborhood, light moves at c.  Over a large neighborhood, you have to account for curvature, such as when comparing what two observers at different points in curved space-time see.