Original question: Why is travelling by time impossible?
In advance: Let us be very clear that travelling through time is obviously possible!
In fact, everyone is doing it continuously.I have to come across the first one who, like me, has not travelled through time to get into the here and now.
I suspect that travelling here with time is meant to travel from any moment to a time already passed, i.e. travel back.
Here too, we must be very clear: we do not know whether that is possible or not. There are models of the general theory of relativity in which we can indeed find closed time-like paths[1 by Space-time!A very well-known man — Kurt Gödel[2 found this solution of the Einstein equations.
This means that in any case it is not impossible on the basis of the known laws of nature.Nonetheless, there are very good reasons to think that this is not possible. Perhaps the most important is simply that the concept of causality is jeopardised. For example, consider the question of what would happen if you traveled back in time and murdered one of your ancestors before you were born, making you never to be born to travel back even later in time.
But in addition, General theory of relativity is a classical theory, which does not take into account any quantum effects.It is quite possible that this means that such closed, time-like paths cannot physically exist.
But remains true that we do not know at the moment that it is impossible.
Because of the paradoxes.
The grandfather Paradox
By traveling to the past you could kill your grandfather and prevent your birth.
By travelling to the future you could experience your own funeral.
The butterfly paradox.
By catching a butterfly in the distant past, for example in the Trias, a cascade of events would not take place and your present would look very different (chaos theory).
So there are no physical arguments against time travel, but philosophical.Remember that time in reality does not exist but the result of conscious observation. Consciousness is necessary to experience time. There is only one timeline and that is ours.
The speed of light is the greatest possible speed in our universe.Actually, it’s not just the speed of light, but the speed of everything that has no resting mass.
That speed depends on a number of properties in our universe.Why our universe has exactly those features is unknown. Maybe there are also universes with a different speed limit.
Theory of relativity tells us about the relative time lapse in objects that have a different speed.
Quite simply put: the quicker you move through space, the less you move through time.
At the speed of light, moving through time stops: From the point of view of the light, time is silent.
To travel back in time, you should go faster than the light.
But that is impossible because of the properties of our universe.*)
It is theoretically possible to travel to the future at a different speed.
When you approach the speed of light in a spaceship, you will experience much less time than people on Earth.However, this is only theory. In practice, we don’t get a fraction of that speed yet.
Conversely, you would experience more time when you are close to a very heavy object.Think of a black hole or neutron star. This is also purely theoretical: the fastest probe would take hundreds of thousands of years to get to the nearest heavy object. Having arrived there we do not have materials that remain very in such an environment.
Basically, even the GPS satellites travel a bit through time.But it’s about millionth of seconds.
Sean Carrol has suggested the idea that time and entropy are related.Since entropy can only rise this gives a direction to the time. Because when you look at the smallest level, each reaction can also take place reversed. However, on a macro scale this is different: falling shards will never fall into each other as unbroken glass.
The conclusion that normal matter can never reach the speed of light and that light can never go slower is derived from the theory of relativity.This theory tells exactly how objects behave, but not why.
*) It is in any case impossible for matter and light.However, it has been suggested that there are other particles that travel back in time. Although that is not a generally accepted idea, it is also not totally excluded. It would not change very much: we would still not be able to travel back in time.
In principle, you have always been travelling through time, though that is going to be from today to tomorrow.If you follow the twin paradox, you can travel through time at different speeds as shown in the example with the younger and older brother.
In theory, you could travel for a time at a speed that is at the speed of light and can stay away on your own clock for a week and when you come back on Earth you can find that everything and everyone here is 2 years further. You will have to travel at a speed that is at 99,998% c.So practically speaking, it is still a bit tricky.
Otherwise, somewhere of every Micro or nanosecond a copy should be kept from everything and where you can go.As far as the future is concerned. And then you can go speculating we live in the very first second or is there already a second for us?
And where would all that be stored?In another dimension sometimes?
This is NOT an answer, just a personal opinion.
Because time does not exist.Time is not like a movie that washes you forward and backward to your heart’s content. There is only a reconstruction and an expectation pattern that we conveniently scale linear. (Or circularly as on a watch).
Time exists by pardon the observer and the information carrier (the fastest is light).That doesn’t mean you don’t have a change of state.
The only thing that exists is “now”.As I write this, a countless number of “Nu’s” have gone by. Our memory ensures that we remember what has been. And calculations and expectant patterns can give us a very reasoned gamble to the future. Otherwise we could not plan anything. But like the Moody Blues it already described “Thinking is the Best Way to Travel”, so also in time. We have invented time to be able to place the past, present and future. After all, speed of light is also a change of situation. A fraction further than before.
My time machine is almost done.There is only a small technical problem. Every time I get in and turn it on to travel back, I step out again.
It’s good that the device then disassemits itself back in time, otherwise I would end up in a tricky timeloop.