Is time travel possible? In films and books, the answer is yes. Numerous fictional representations depict folk either going back in time or into the future. The classic scenario involves a character going back to alter history. The plot often involves the elimination of someone who will, in the future, cause great harm. Would there have been a Second World War if someone had killed Hitler when he was ten? But interfering in the past would raise a number of paradoxes that are not easily resolved. I'll return to this interesting phenomenon later.
If I was of a facile disposition I would mention that in fact, we all travel in time at the rate of 1 second per second. Time is inexorable and, seems to us at least, to move only forward. But that explanation will satisfy no one and in fact, is rather glib and even trite. There is a way to look into the past without violating known universal laws and that is through astronomy. Every time we interrogate the cosmos we see stellar objects as they were, and from our perspective, as they looked in the past. For instance, the nearest star to our system lies 4.3 light-years away. Therefore it takes light 4.3 years to reach us from this relatively close star. If it exploded or ceased to be, we would not be able to register the event for 4.3 years. An example closer to home: our sun is 93 million miles away, and even though the speed of light is a blistering 186,000 miles per second it still takes just over 8 minutes to reach us. I suspect my readership is already aware of this quaint consequence and thus remains unmoved and perhaps, indifferent.
Einstein's breakthrough theories at the beginning of the last century radically altered our perception of how the natural world operates, at the macro level at least. Newton's systematic explanations were overthrown. Although Newton knew that gravity acted over a distance and was aware that this force was related and proportional to mass, he confessed he had no idea how it worked or how the force was transmitted/propagated through space. We had to await the genius of Einstein to understand that time and space are intertwined and that gravity could be explained, simply at least, as mass warping space- the greater the mass the greater the 'deformation' of space. Also, his insight that light has a constant speed, regardless of context, and that it represents the ultimate speed limit in the universe would result in weird time dilation effects. This post is not a review of Einstein's Special and General relativity, so I won't delve any deeper - perhaps in the future? Einstein predicted that time is relative and alters according to velocity and is dependent upon the 'participant's' perspective. At light speed, although the photons/waves take a finite time to reach us from objects in the universe, light 'perceives' reality rather differently. Imagine, if we could ride a photon and we didn't fall off, we would not experience time at all; everywhere and anywhere (unnecessary tautology) would be arrived at immediately. This is hard to conceptualise, but Einstein predicted time dilation based on theory alone, without any practical and experimental validation. Consequent experimentation has shown this to be correct. For instance, orbiting satellites travelling at 17,000 mph experience time slightly less than us mere terrestrial beings. The difference is not great, just a few milliseconds, but it has been verified on numerous occasions. To really observe significant time dilation we would have to travel extremely fast indeed and close to the speed of light. Of course, it is impossible for anything with mass to travel at the speed of light. However, if say you could travel from the Earth at 99.9% light speed and come back to Earth after 50 years, according to the terrestrial viewpoint, everyone on Earth would have aged by 50 years. However, from the traveller's perspective, the journey would have only taken 2.24 years and consequently, he would have aged accordingly. Some physicists consider that time does not exist, in any 'real' sense at all, and is no more than an illusion, although admittedly a stubbornly persistent illusion.
It seems that significant time travel to the future is a theoretical possibility, but it is a one-way ticket. Time travel into the past violates the laws of physics, as we currently know them, and as intimated earlier would create strange and wonderful absurdities. This can be expressed using the 'Grandfather Paradox': consider that you could travel back in time and murder your grandfather before he sired your father. Accordingly, if the father did not exist then neither could the time traveller and therefore you could not have killed your grandfather (refer to diagram). There are those who reconcile the 'Ultimate Paradox' by positing alternative future narratives. So, if you killed your grandfather, there would be a bifurcation of reality where your grandfather continued to live and an alternate reality where his death would result in your nonexistence. Indeed, a select group of philosophers consider taking this thought process even further and consider that every action we undertake in the real world results in the formation of a host of, noninteracting alternative futures. This is not easy to conceptualise and raises many issues that are difficult to resolve from our interpretation of how the Universe works. There could be other explanations, but it has to be acknowledged that perhaps our minds are just not up to tackling this problem. Evolution has moulded our brain to cope with the everyday vicissitudes of life and is not designed to pontificate on the Ultimate Questions of our existence. The late, great Stephen Hawking believed that time travel to the past was an impossibility, and I'm not going to disagree with this towering intellectual giant. This has not stopped speculation on possible ways to return to the past. One consideration promotes the idea of 'Wormholes' in the fabric of the universe, which connect alternative possibilities in both time and space. The problem is we have found no evidence to date to suggest that wormholes exist. There are pundits who consider that entering a black hole would whisk the traveller magically back in time. I'm sure my readers can see the problems with this so-called, solution.
So, as far as we can tell, travel to the future is a possibility, given the right conditions. A return to the past is not so favoured by Natural Law, although I do believe there are equations that predict its possibility. If only we could get hold of 'exotic matter' that doesn't seem to exist. Quite a conundrum.
Anyway, enough of these bollocks, my next post will concern the battle of Crecy.