[vanman]

Originally Posted by Hugh

Ah, the "many worlds" interpretation of quantum physics, utilising the quantum decoherence mechanism; once again, causality violations would need to occur for this to be true, as travelling to the past would create a "branch" which would diverge from the time-travelling alien from another dimension's original time-line (instead of collapsing the standing wave (cf the Copenhagen Interpretation), there would be a quantum superposition) thus breaching the information transfer.

But surely what you are saying is only based on the known knowledge that we have
Therefore the theory may be proven wrong in a future dimension. i refer you to the
String theory

http://en.wikipedia.org/wiki/String_theory which asserted that strings are really 1-dimensional slices of a 2-dimensional membrane vibrating in 11-dimensional space.

Levels of magnification:
1. Macroscopic level - Matter
2. Molecular level
3. Atomic level -- Protons, neutrons, and electrons
4. Subatomic level -- Electron
5. Subatomic level - Quarks
6. String level

An intriguing feature of string theory is that it involves the prediction of extra dimensions. The number of dimensions is not fixed by any consistency criterion,[dubious – discuss] but flat spacetime solutions do exist in the so-called "critical dimension". Cosmological solutions exist in a wider variety of dimensionalities, and these different dimensions—more precisely different values of the "effective central charge", a count of degrees of freedom which reduces to dimensionality in weakly curved regimes—are related by dynamical transitions.[14]
One such theory is the 11-dimensional M-theory, which requires spacetime to have eleven dimensions,[15] as opposed to the usual three spatial dimensions and the fourth dimension of time. The original string theories from the 1980s describe special cases of M-theory where the eleventh dimension is a very small circle or a line, and if these formulations are considered as fundamental, then string theory requires ten dimensions. But the theory also describes universes like ours, with four observable spacetime dimensions, as well as universes with up to 10 flat space dimensions, and also cases where the position in some of the dimensions is not described by a real number, but by a completely different type of mathematical quantity. So the notion of spacetime dimension is not fixed in string theory: it is best thought of as different in different circumstances.[1

In the universe as we experience it, we can directly affect only objects we can touch; thus, the world seems local.
Quantum mechanics, however, embraces action at a distance with a property called entanglement, in which two particles behave synchronously with no intermediary; it is nonlocal.
This nonlocal effect is not merely counterintuitive: it presents a serious problem to Einstein's special theory of relativity, thus shaking the foundations of physics.