Shakespeare now writes “travelresourcesonline“. The paradox is, where did “Hamlet” come from since Shakespeare only wrote it after he had already seen your copy. No, you can’t travel back to the past because if that were possible there would be hoards of time-travelling tourists who went back in time to witness some important historical event or other. No hoards of photo-snapping tourists have ever been documented being present at Custer’s Last Stand, the Battle of the Alamo, the sinking of RMS Titanic, or any one of thousands of similar historical events. Yes, you can travel back in time but only into a parallel universe. If you shoot yourself but it is another you in another universe, no paradox arises. You travel back in time to have Shakespeare autograph your copy of “Hamlet” but in that parallel universe Shakespeare can now write “Hamlet” based on your copy and no paradox results. However, the one point I find interesting is that if you end up in the future, or in the past, are you really in the future or the past? No, the only time you can exist in is the present, your right here and NOW time. It might be a different time from what you previously knew, but still wherever and whenever you exist, you only exist in the NOW.
# Is time travel possible? It could already be the case that time travel has been documented at the quantum level although that could be open to interpretation. Before I get to the specifics, I just need to point out that with respect to the laws, principles and relationships of physics, time is invariant. Operations in physics remain invariant in time whether time is moving as we normally perceive it (past to future) or back to front (future to past). For example, gravity would operate as per its normal grab-ity self in a world where time flowed backwards. There’s many an operation one could film that when the film were run backwards, one wouldn’t be any the wiser. Tree branches blowing in the wind comes to mind, or the coming together, collision, and rebounding or separation of two billiard balls. Okay, having established that when it comes to physics, physics doesn’t care which direction time is flowing, there will be no violations in those laws, principles and relationships of physics future to past, we now come to the delayed double slit experiment.
In the normal double slit experiment, you have an electron gun that fires one electron particle at a time, such that one electron completes its journey before the next one is fired, at two side-by-side slits. If one or the other slit is open, the one-at-a-time electrons pass through the open slit to a detector screen behind the slits. The detector screen gets hit in nearly the same spot every time after each and every electron particle passes through the single open slit. That is straight forward. If both slits are open, the electron shape-shifts into a wave (how I don’t know), passes through both slits (as only a wave can), morphs back into a particle and hits the detector screen. The difference is that after enough electrons have been fired, and have passed or waved through the double slits, the hits on the detector screen are not in just one or two spots but all-over-the-map, albeit all-over-the-map in a classic wave interference pattern. Okay, that’s the classic experiment.
Now we do a variation on the theme, the delayed double slit experiment. Electrons are fired one-at-a-time, with both slits wide open. An all-over-the-map classic wave interference pattern should appear on the normal detector screen after enough electrons have been fired. However, in addition to the normal detection screen, there are two other detectors positioned behind the normal detector screen that are each in an exact line-of-sight with each of the two slits. The electron is fired. It morphs into a wave and passes through both slits then morphs back into a particle. But before the electron, which has already passed through both slits, can hit the detector screen, the detector screen is removed to reveal behind it the other two line-of-sight detectors. Now presumably once the electron has passed though the double slits it’s too little too late to change its mind about where it’s going to hit. Only a tiny few should be detected by the two line-of-sight detectors aligned with the two slits. Alas, each and every electron will be detected by one or the other of the line-of-sight detectors. It would appear that the electron CAN change its mind after it has already gone through both slits and instead appear to have gone through one or the other of the two slits. One interpretation is that the electron, after having passed through both slits, realised the gig was up, travelled back in time, retraced its path and passed through one or the other slit.
As an aside, the late Nobel Laureate Richard Feynman noted that the double slit experiment went to the heart of quantum weirdness. I mention this because it was the same Richard Feynman who suggested that a positron (an anti-electron) was just an ordinary electron that was going backwards in time.
# Is time travel possible? I have several other points to make about the concept of time travel.
Firstly, there is Stephen Hawking’s idea of a Chronology Protection Conjecture which postulates that there is some as yet undiscovered law of physics which prevents time travel to the past and thus makes the cosmos a safe place for historians to strut their stuff.
Secondly, it has been said that you cannot travel farther back in time than the date your time travel ‘device’ was constructed, be it a wormhole or some other gizmo. So if some genius builds a time travelling ‘device’ in 2014, he’s not going anywhere into the past. But in 2015 he can travel back to 2014 and in 2114 he could travel back to any time between 2114 and 2014. The analogy is that you cannot travel through a tunnel prior to when that tunnel was built. Thus, we don’t see human time travelers because no human time travelling ‘device’ has yet been constructed. The flaw there is that doesn’t prohibit ET from visiting who might have constructed a time travelling ‘device’ millions of years ago. Recall those pesky UFOs though they don’t seem to cluster around significant terrestrial historical events so maybe ET doesn’t care about our history and are just here on vacation from their future.Business Traveller Flying to London? A London City Guide