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Space-Time Cloak Could Hide Actual Events
An anonymous reader writes "My first thought was, a hypothetical space-time invisibility cloak? That must be what hypothetical crime-fighting Einstein wears when he wades into the fray! Sadly, the researchers who thought up this trick to 'hide events' say that the metamaterials we have on hand will only allow for a nanoscale demonstration at best."
I will post my reply using my spacetime browser but you won't see it until several nanoseconds later!
When the foot seeks the place of the head, the line is crossed. Know your place. Keep your place. Be a shoe.
mwahaha! if i'm never a part of events intersecting the light cone i dont exist!
oh shiii-
Ice Cream has no bones.
Maybe we just can't see the ones that get it right.
rewriting history since 2109
I'll believe it when I don't see it!
So, there is no magical disappearing of time or events or 4D cloaking of spacetime.
It's slightly more subtle than that. IIUC, it's impossible to detect something happening in the cloaked region of space. So in the chicken crossing the road scenario, to an outside observer, it looks like the cars travel at a constant speed and the chicken "magically" teleports from one side of the road to the other.
The idea that something is in one state or another without being able to detect intermediate states is not new to physics. If you attempt to "watch" the transition between two eigenstates you will always measure one state or the other. We can have a mathematical model of how the wave function evolves, we can do experiments that demonstrate that the wavefunction must have been in a state that our mathematical model describes as a superposition of eigenfunctions, but we can never measure that superposition.
In QM terms, I suppose the chicken would be described as "tunneling across the road"
(note that I have no reason to suppose there is any relationship between 4d cloaking and QM tunneling - it's merely an analogy that came to mind)
Tim.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
Why do you think after the second book they no longer care which house wins. Griffendorf keeps on getting a bunch of points taken away do to slipping accidents in the girls dorms.
If something is so important that you feel the need to post it on the internet... It probably isn't that important.
Light isn't special. It is just another particle (photons). It doesn't affect spacetime in any way except by the gravitational force which happens to be tiny since it is so light (pun not intended).
A photon (most likely) does not have mass. Although, interestingly enough, it does have momentum. It is affected by gravity, such as passing by a star, because spacetime is curved and the photon is merely following a geodesic (generalized notion of a straight line through curved space)..
Light isnt sped up going around black holes, though it is red-shifted.
Yes, in principle if photons had mass that could lead to something like dark matter.
However, in practice we know this isn't the case. First of all, if photons had mass (and quantum mechanics as we understand is roughly correct), this would modify a whole slew of predictions in all kinds of bizarre ways (down to fundamental things like the number of particles we observe and the stability of matter). Basically, the only way to match all our experimental data is with a massless photon.
Even beyond that, however, the measured distribution of dark matter (which we can infer based on things like galactic rotation, gravitational lensing, large-scale structure in the universe, etc.) does not match the measured distribution of photons (which we can calculate based on the positions of known light-emitters, like stars).
It's a neat idea, but appears not to be the case in our universe.
It's all relative. Actually it is sped up, but not in the way you think. They've found that if a gravity well is strong enough, it actually pulls spacetime around it. If you were to shine a beam of light while based on spacetime that is moving, you in essence create a beam of light that is moving faster than the speed of light, at least for an observer standing on spacetime that is not moving.
They need to up date it to: "How to not be where you are."
The Kruger Dunning explains most post on