String theory ? Why would you need that ?
Hi everybody,
Wow, I've been gone for a couple of days and all of the sudden there are like 100 messages to catch up. Neat

.
Okay, some thoughts:
Kmguru said:
Well if we can not use photons to communicate (because it is too slow). We may be able to piggyback someother particle (gluon or boson or ?) that can appear to travel FTL after getting a boost from the photons namely lasers. Another way could be to make a microscopic tunnel in space to bridge the otherside (is it same as quantum tunneling?). Can the string theory help in our quest?
The problem with other particles is that they are forced to travel in "empty space" at speeds not exceeding the speed of light. Gluons are particles that "glue" quarks together, and they have not been verified to exist separately (quarks and gluons always recombine to form couples of quark/antiquark to form a meson particle type, or 3 quarks couple to form a hadron particle type). A boson is a general classification type for particles: we divide all known particles in two categories: bosons and fermions, depending on spin. It's not a particle itself.
Quantum tunneling is a phenomenon were a particle leaks through what is called a "potential barrier". For example: an alpha particle (2 protons + 2 neutrons) can leak out of a nucleus to emit alpha-radiation. Or, if you shoot a particle at a wall, it can leak through the wall (quantum mechanics predicts that if you throw a ball at a wall, there's a slight possibility that the ball will go straight through it... However, the probability is very small). Quantum tunneling is hence the phenomenon that a particle passes an obstacle it normally can't pass; it seems that the particle found a "tunnel" connecting the two opposite sides of the barrier, making it possible for the particle to pass the barrier (while it normally can't, because it hasn't got enough energy).
The reason why I mentioned quantum tunneling is that experiments and calculations suggest that particles pass a barrier faster than the speed of light (it's a little more complicated than this, since there speed for a particle is not always speed as we think it is).
Practically speaking, I don't think you can use quantumtunneling for interstellar communication, because:
- The tunneling probability lowers fast if the width of the barrier to tunnel through increases. The probability that a particle tunnels through a 4 lightyears barrier is nonexistent.
- The barrier here would be the empty-space gap between transmitter and receiver, but the exact location of where the particle will pop out is unknown. So instead of tunneling to the receiver, your particle with the information might appear totally out of direction. You would need some sort of "focussing" here, and I don't think the tunneling phenomenon is understood well enough to do this.
About string theory: I am not familiar with the theory, but I do know that it is still very hypothetical. There have been a couple of experiments that can be explained if you assume string theory, but personally I think there's just not enough evidence to support string theory yet.
Links on quantum tunneling:
http://www.aei-potsdam.mpg.de/~mpoessel/Physik/FTL/tunnelingftl.html
Extensive list of literature on the subject. Technical.
http://www.biols.susx.ac.uk/home/John_Gribbin/quantum.htm#Photons
Basic explanation of what quantum tunneling and the experiments are about.
On request: some links on String theory:
http://www.physics.ucsb.edu/~jpierre/strings/index.html
Not too technical introduction to string theory.
http://superstringtheory.com
You probably know this one. The "official" homepage of string theory (even though it's only the claim that sounds prestigeous). Excellent introduction though.
Chagur, wet1:
Considering that the effect of gravity is considered by some to be almost instantaneous, like on the order of a billion times faster than light, I'm surprised that no one has mentioned the possibility of using it, or an aspect, to communicate vast distances.
So how do we effect a mass sufficiently to generate the changes needed to make a message known?
I agree with wet1 that not enough is known about gravity to be able to say something about communication techniques. I am now sure about this, but I believe gravity is also restricted to the speed of light. In general relativity, gravity waves spread out at the speed of light. In the attempts to describe a quantum theory of gravity, the graviton is probably also restricted to the speed of light (just for the sake of causality, whether the experiment confirms this is unknown to me). And even if gravity travels faster than light there's still a problem: as wet1 mentioned, how would you affect a mass to produce large enough fluctuations in gravity waves in order to make them detectable several hundreds of lightyears further ? (The waves become smaller in amplitude as they travel further).
And finally, Kmguru:
Not all particles will tunnel the space but some will. Those atoms which are travelling in the tunnel eventually loose their energy level and drop out of the tunnel to normal space. To control the distance we may have to control the applied energy.
The tunneling probability indeed depends on the energy of the incoming particles. However, we're talking about probabilities here, so even with a "fixed" energy, there is still a large spread on where a particle has a large enough probability to pop up after tunneling.
Reason is that, on ground, the transmitter will be the size of a house.
I'd make that a few hundred times larger

. You'd have to give the particles a lot of energy, and that would require particle accelerators (and most of those don't fit in your basement).
The only thing I have not figured out is how do you aim the transmitter to the receiver plate since aiming in normal space may not work.
Hrm.... I think directional aiming is sufficient, assuming the tunnelbarrier is uniform in all directions (if the barrier is noticeably smaller in one direction, the distance for tunneling shortens, and hence the probability for emerging there increases).
Bye!
Crisp