There is an ongoing PBS TV series (also several books and also a website) called “Closer To Truth”. It is hosted by neuroscientist Robert Lawrence Kuhn. He’s featured in one-on-one interviews and panel discussions with the cream of the cream of today’s cosmologists, physicists, philosophers, theologians, psychologists, etc. on all of the Big Questions surrounding a trilogy of broad topics – Cosmos; Consciousness; God. The trilogy collectively dealt with reality, space and time, mind and consciousness, aliens, theology and on and on and on. Here are a few of my comments on one of the general topics covered – Is time travel possible?
# Is time travel possible? Actually I personally don’t believe time exists. Change exists, and time is just our measurement of rate of change. IMHO time is just a concept. Time is a mental construct that helps us come to terms with change. Some cosmologists say that time was created at the Big Bang, as if time were a thing with substance and structure, but I challenge them to actually create some time in front of their peers or maybe a TV audience or at least produce a theoretical equation or two that would create time. In the meantime, here’s a trilogy of points.
First, the concept of time travel is one of those fun parts of physics. Whether true or not, it is entertaining to play the ‘what if’ game. If nothing else, the concept makes or forces one to think about the nature of reality.
Secondly, Einstein and others have postulated that time travel is a theoretical reality and I’m not in their sort of league that I can dispute the theories. I’ll leave that to others who know the field inside and out.
But thirdly, and most importantly, you can never actually be in the future or the past, only in the future or the past compared to where and when you are now. In other words, no matter how you slice and dice things, you exist in the where-ever and in the whenever in that where-ever’s or whenever’s NOW or in other words in the present. You cannot literally be in any future or in any past since you only experience the NOW which is the present. If you should somehow travel back one hour, you would still experience things as belonging to NOW. If you sleep for one hour then wake up, you are in the future relative to when you went to sleep, but you still find yourself in the NOW.
# Is time travel possible? The answer is both yes and no. Yes, we can travel into the future at one second per second, we do that anyway whether we like it or not. Yes we can travel into the future at a slightly quicker rate by going to sleep or otherwise having our sense of consciousness, our awareness of rate of change (which is what time really is or measures) incapacitated. You get drunk and pass out and the next thing you know you are 12 hours into the future. Yes we can travel into the future as outlined by Einstein’s twin ‘paradox’ where one twin travels at a very high rate of speed outward bound, stops and returns to home base, while the stay at home twin, well, stays home. Upon their reunion the travelling twin finds their stay at home twin to be far older, so the travelling twin has travelled into the future more rapidly than would otherwise have been the case. Yes, you can travel back in time, in theory, according to the apparent theoretical properties that wormholes or black holes can have. No, you can’t travel to the past because of all of those nasty paradoxes. I like the variation on the grandfather paradox whereby you travel back just one hour into the past and shoot yourself dead. That’s a novel way of committing suicide! The other paradox I like is when you go back in time to have Shakespeare autograph your copy of “Hamlet”. Shakespeare isn’t home but the maid promises to have him autograph your book when he returns. Alas, your timing is slightly off and Shakespeare hasn’t yet written “Hamlet”, so when he receives your copy from his maid to autograph, he reads it, and after you return to Shakespeare’s home and receive back your now autographed copy and return home to your own time, Shakespeare now writes “Hamlet”. 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.
Thirdly, presumably your time travelling ‘device’ is fixed at some sort of celestial coordinates. Because everything in the cosmos is in motion, when you re-emerge into that cosmos after starting on a time travelling journey, while you may be at those same fixed celestial coordinates the rest of the cosmos would have moved to differing celestial coordinates. So, if you start out in London you won’t end up in London on down, or up, the time travelling track. Finally, the concept of your, or the future or of the past or your past is only relative to what you choose as some fixed point. If you pick your date of birth as that fixed point, then clearly you are now in the future relative to your date of birth. If you pick the concept of an ever ongoing NOW, the present, as a fixed point, you are neither in the future or the past relative to the NOW nor will you ever be. That of course doesn’t mean you can’t recall your past, what existed before your NOW (although the past in general is more abstract) or plan for your future after your NOW (although the future in general is beyond your control).
# Is time travel possible? There’s yet another form of time travel, or at least the illusion of time travel, and that’s via the cinema. Films and TV shows involving time travel are many and often legendary. But that’s not quite the medium I wish to explore here. One can program time travel into a computer simulation. You can have a video game where the characters travel backwards (or forwards) in time, or have a software program that loops around back to the beginning. Now the question is, might we be characters or virtual beings in a Simulated (Virtual Reality) Universe? If so, the software programs that run our virtual show might allow for time travel, or virtual time travel, yet still time travel that would appear to us to be quite real. Now where does our sense of deja vu really come from?
# Is time travel possible? There is one other form of pseudo ‘time travel’ towards the future that can be debunked. Presumably the only way you can know what the future brings, without benefit of any theoretical ‘device’ that can propel you there at a greater rate of knots than at one second per second, is to stay alive. Once you kick-the-bucket that’s it. Your second per second journey towards the future is over. It’s a pity that that worthless stock you hold just happens to sky-rocket to fantastic values within a week of your demise, or maybe you’d really like to know if ET exists but the discovery happens a few days too late as far as you are concerned. Of course some might claim an afterlife will enable you to keep up to date with future happenings from that heavenly vantage point high up in the sky, but apart from that, there are those who claim to have led past lives or existed in past incarnations. Thus, you can still continue your journey to discover what the future holds by passing on to another body via being conceived again (and again and again). There’s one huge problem however with ‘remembering’ alleged past lives. Your mother’s egg cell cannot remember your past lives. Your father’s sperm cell cannot have any recollection of your past lives. Therefore, the you that comes to pass at conception cannot hold any memory of past lives. So, where did your memory of past lives come from? Might I suggest that it was internally generated out of wishful thinking, that perhaps a belief that you existed in the past will give rise to a belief that you will exist again in the future, and as a pseudo form of afterlife and as a pseudo form of ‘time travel’ that gives you comfort. Anyway, that concept is a really far out methodology of ‘time travel’ but one which can be dismissed despite the many people who seemingly believe that they indeed have ‘time travelled’ towards their endless future via this method.
Science librarian; retired.