However, you might wonder what does Time travel do with these quantum theories! In this post, I would not discuss or analyze whether the quantum theory itself is valid or not. Rather I would concentrate on analyzing whether the parallel universe concept is applicable for Time travel or not and if yes, how it is applicable and so on.
Traveling to the past:
We know how Einstein's time dilation concept help us travel to the future of Earth's time but there is no concept that says traveling to the past is possible. So, quantum physicists came up with a theory that what if there are multiple universes or parallel universes exist. What they mean by parallel universe is that universe besides universe. That means that at the same time, multiple instances of everything exist in parallel and each moves at their own fabric of Time and space.
The fundamental idea behind this theory solely from the weird or spooky behavior of quantums. Quantum mechanics demands or claims that an electron exists at one point of space when we observe but the same electron exists everywhere in the universe if we don't observe. This is what the outcome of the double-slit experiment. Instead of passing through a slit as one particle, electron split itself into two instances (like how a wave does), pass through both the slits and meet (cut across) each other in the other side of the slits.
In outer space what we have is nothing but vacuum and that's why all the experimental determinations have been made in vacuum. However, the vacuum is not really empty. The vacuum has energy associated with it, called the vacuum energy. This vacuum energy can perhaps be changed in certain cases. When vacuum energy is lowered, light itself has been predicted to go faster than the standard value 'c'. This is known as the Scharnhorst effect.
This experiment leads us to various ideas on how electron or photon behaves. This experiment does not only conclude that an electron behaves like a wave or like a particle depends on whether it's observed/realized by external object or not but it also demands that an electron can exist at different points in space simultaneously. Even inside an atom, an electron can exist simultaneously in different orbits! Lets call them as 1st instance and 2nd instance for easy discussion. The theory says that it may be possible that the 2nd instance of the same electron joins with set of 2nd instances of other electrons and atoms. That may form 2nd instance of the same atom. As we move upwards in the process, eventually, there could be 2nd instance of you, me, everything in this universe! The theory also demands that it could be possible to have more no of. universes!
Einstein also analyzed the possibility of traveling to the past. It may be possible that if we travel faster than the speed of light, we would travel into our own past! but his analysis and experiments didn't support this idea because according to him, the following facts conclude that traveling to the past is hardly possible using for us.
- The relativistic momentum of a massive particle would increase with speed in such a way that at the speed of light an object would have infinite momentum.
- To accelerate an object of non-zero rest mass to c would require infinite time with any finite acceleration, or infinite acceleration for a finite amount of time.
- Either way, such acceleration requires infinite energy. Going beyond the speed of light in a homogeneous space would hence require more than infinite energy, which is not generally considered to be a sensible notion.
- Some observers with sub-light relative motion will disagree about which occurs first of any two events that are separated by a space-like interval. In other words, any travel that is faster-than-light will be seen as traveling backwards in time in some other, equally valid, frames of reference, or need to assume the speculative hypothesis of possible Lorentz violations at a presently unobserved scale (for instance the Planck scale). Therefore any theory which permits "True faster than Light" also has to cope with time travel and all its associated paradoxes, or else to assume the Lorentz invariance to be a symmetry of thermodynamical statistical nature (hence a symmetry broken at some presently unobserved scale).
- While special and general relativity do not allow superluminal speeds locally, non-local means may be possible, which means moving with space rather than moving through space.
There is an experiment that shows the possibility of traveling more than the speed of light. In this experiment, a vacuum is produced by bringing two perfectly smooth metal plates together at near atomic diameter spacing. It is called a Casimir vacuum. Calculations imply that light will go faster in such a vacuum by a minuscule amount: a photon traveling between two plates that are 1 micrometer apart would increase the photon's speed by only about one part in 1036. Accordingly there has as yet been no experimental verification of the prediction.
A recent analysis argued that the Scharnhorst effect cannot be used to send information backwards in time with a single set of plates since the plates' rest frame would define a "preferred frame" for FTL signalling. However, with multiple pairs of plates in motion relative to one another the authors noted that feedback loops of virtual particles would create "uncontrollable singularities in the renormalized quantum stress-energy" on the boundary of any potential time machine, and thus would require a theory of quantum gravity to fully analyze.
Other authors argue that Scharnhorst's original analysis which seemed to show the possibility of faster-than-c signals involved approximations which may be incorrect, so that it is not clear whether this effect could actually increase signal speed at all.
Having said that, lets come back to our analysis. Consider only two instances or two parallel universes to keep it simple. While Einstein's theory of relativity doesn't support traveling to the past much, quantum physicists claim that it may be possible to travel to the past, not our universe, but to our parallel universe. In other words, you can start from 1st instance of an universe and move to the past of the 2nd universe where you might have not been even born! Lets see 'how' in my next post!
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