[Pickel B Gravel]

Even if humans could somehow create a way to travel through time, it would be limited to the lifespan of the person or machine doing the traveling. After all, wouldn't traveling back in time simply "deconstruct" the time machine or "regress" the person's aging to his birthday and no further? But a time machine and person cannot travel past the point in time in which they were created because all that time traveling is is undoing what has already happened or what will happen...and that includes aging and entropy, right? How can a time machine or a person travel to a time before they came into existence? Time traveling to the past would end on the day the time machine was created. The same applies to traveling to the future: it would be impossible for a person to travel past his time of death. We are limited to the day we die. A lot of people believe time traveling would simply create parallel universes, but I see no evidence for that. Time travel would be limited to the lifespan of the person or machine. It's interesting that it's mostly round earthers who buy into the nonsense that time traveling thousands of years into the past and thousands of years into the future is possible (in theory). That's not thinking critically. But here I have debunked the whole thing.

[Lord Dave]

Humans travel through time all the time.  You're doing it now.  Forward, specifically.


Backwards has math to back it up.

[Dr David Thork]

Maybe you need to take a step back from a human time traveling and look at a subatomic particle or something simpler?

A sub atomic particle has various properties to manifest it in the physical universe. Its location, its temperature, its electrical properties, its mass etc. Its time could also be a said property. We know how to change the property of many things. Want to change the temperature? Add or remove energy. Want to change the location? Move it. Want to change its time .... mmm. Well this is a property we don't know how to manipulate as of yet. But if you could set its date 100 years before, it should manifest itself in the universe 100 years earlier.

If I look at something 100 light years away, the light hasn't updated its properties and I see the thing as it was 100 years ago. Not as it is now. So using photons I can see back in time using proximity to moderate the property. And I can also slow a subatomic clock by flying it around the world. I'm getting closer. That really is time travel. So energy is the thing I manipulate to change temperature, movement is the thing I can use to change time.

So I will disagree that we can't time travel using a machine. I only need to get in something very fast for a long time and I can go into the future. Thank you relativity.

So now I can see the past, and go into the future. The problem is I can't see the future or go back to the past. The kind of useful ones that allow me to see something before it happens or go back and do something differently.

Now I could see the future, but that would require me to be a long way away and start accelerating to the thing I want to see. So if I'm 100 light years away from earth and I can see WW1 is about to end, I could accelerate towards the earth and find out who wins before anyone else at my starting location knew about it. Because to us the present earth is 1918. But I'd have to get back faster than the light to make any use of this info such as putting £100 on the British to beat the Nazis.

The problem comes that I could only see as far as 2018 because by that point I'm here. I can't go any closer as I have arrived. I'm at the datum point. Figure how to get me through that and we'll go pick some lottery numbers together.

And I can go into the future by travelling very fast like my subatomic clock, but I can't go slower than not moving to get me into the past. Again I have the datum of not being able to go slower than being stationary. At which point I just tick along with entropy (time) like everyone else.

But something I wonder ... if the solar system is moving and the galaxy is moving and the earth is moving etc, I'm always moving. Is that what is making time happen? If I could just get myself to a place in space where no gravity effected me at all and just be still, would time also stand still for me? Would my watch stop if I could get outside of the universe? I'd again theorise it probably should, because sure time is a property of this universe. Outside of the universe there are no physics ergo no time. Probably why God is immortal 

I also wonder that if I froze something down to absolute zero, have I in effect slowed its time down to zero. Its electrons stopped, there is no movement, it doesn't change or age in any way. And If I heat things up, reaction happen faster as though I'm pushing them into the future.

So from dimensional analysis everything can be boiled down into units of Mass, Length, Time and Temperature. Or gravity, distance, time and heat, if you like. So I would theorise that Time is a function of Mass, Length and Temperature and by changing any of these things, I could in fact time travel, assuming I survived the freezing, light speed or gravity well. I'd just need one hell of a clever machine to do it.

[Skeptic]

The only way I know how to time travel, theoretically, would be to use a space-ship and a black hole. Suspended animation for humans would also have to be available, (we're not too awfully far away from that now, so let's just pretend it already exists).

According to Einstein's theory of general relativity, massive objects create distortions in space and time. Near a black hole, these distortions become so strong that time behaves in unexpected ways.

Imagine that we are on a spaceship near a black hole. We drop a clock into the black hole and compare its time to that of our onboard clock. The falling clock runs progressively slower. It never crosses the event horizon, but stays frozen there in space and time. The falling clock also becomes continuously redder, since its light loses energy as it escapes from the black hole's vicinity.

By contrast, if we were falling with the clock, time would appear to behave perfectly normally. We would see no slowdown as we approached the event horizon. We would cross the horizon without any perceptible change, and our color would not appear to change. This is the principle of relativity: things can appear different depending on whether you are moving or standing still.

So, using suspended animation to make the years-long journey to a black hole, possibly using a star's gravitational pull to slingshot us at a high enough speed that we run little risk of getting sucked into the black hole and spaghettified before being crushed into a microscopic pulp, then the time distortion would hold us near the vicinity of the event horizon for what may seem like hundreds if not thousands of years as observed by Earth, but to us, time would be running perfectly normally; the whole trip may feel like just a few years or so, (forgetting for the moment that we aren't in suspended animation dreamland), but in reality, by the time we got back to Earth, we'd be in the distant future. We might not like what we find, either. Suppose for a moment that humanity had evolved into almost alien looking humanoids; we'd look like Neanderthals to them, and they might even want to put us in a People Zoo. Or, worse yet, we come back to an Earth that has been long-ago destroyed by a massive meteor, or struck by a solar flare that wiped out all life on Earth. Not a pretty picture.

In regards to going into the PAST though, I have no Earthly idea; one would probably have to start getting into quantum mechanics in order to accomplish that feat. It's interesting to note though that theoretical physics working at the LHC (Large Hadron Collider) have observed particles which appear out of nowhere then disappear just as quickly, and in a random fashion. One of their theories is that these particles are actually popping in and out of the space-time continuum. Where do they go? They don't know; they suggest that perhaps when they disappear here, they pop up in another time or a parrelel universe, where scientists in that universe/time are observing the same particles doing the same things, scratching their heads just like we are, asking themselves the same questions we're asking. 

[Cain]

We drop a clock into the black hole and compare its time to that of our onboard clock.

But how would you see the clock you dropped into the black hole if light can't escape, radio waves can't escape, etc?