Ok, Here’s the question – Is time travel possible?
Here’s my thoughts:
Yes. I am sitting here writing this little piece of nonsense, the ramblings coming out of my brain. I am writing this today in 2020. Yet you, the reader are reading this in the future!
Okay, okay. So maybe it’s not time travel, BUT, you are reading my thoughts that were laid down in the past. And as far as I know, time travel is possible, and you can go into the future. It’s simple. Pull up a chair, sit down, and wait….instantaneously you have and continue to arrive in your own future! As far as we know, on macroscopic physical scales, the only kind of time travel that works is moving into the future. You can sit around and wait, or you can scoot off at very high velocities and exploit relativistic time dilation to alter the passage of time you experience compared to the universe around you. (Talk to Einstein about that.)
But, let’s say you could travel back in time, but not space. That is you would travel back in time, but could not, for instance, go back to Las Vegas in the 1950s. You would arrive in the 1950s in the same space you were when you left, or would you?
Let’s say you built a time machine and decide to travel one month into the past. In a typical sci-fi story, you’ll appear at precisely the same location, just a month earlier. But how does your uber-cool time machine get you to that unique physical place?
On Earth’s surface we’re in constant motion. The planet’s spin has us racing around at about 1,600 kilometers an hour at the equator. The Earth is orbiting the Sun at an average of 110,000 kilometers an hour. The Sun is currently moving relative to the center of the Milky Way galaxy at about 828,000 kilometers an hour, and our Local Group of galaxies is plunging through the cosmos at a velocity of about 2.4 million kilometers an hour relative to the cosmic microwave background. But space is of course expanding, so on very large scales no physical object can be said to be truly at rest with respect to others – it may just be equally not at rest in all directions. So, suffice it to say, we are really moving fast!!
To go back 1 month, and to appear at the same place – your office, Las Vegas, correcting that blunder you made on your first date – you must also move a significant amount of physical distance. And you must do this extremely accurately. This is an incredibly complicated spatial problem.
Let’s take the Earth’s motion around the Sun. A month of orbit corresponds to moving in an arc of approximately 78 million kilometers. During that same period, the entire solar system will have also moved approximately 600 million kilometers around our galaxy, and our entire Local Group of galaxies will have swept through about 1.7 billion kilometers of space relative to the cosmic microwave background. Not only do you need to find a way to bridge those kinds of distances, but you also need to get it correct to within a part in a trillion.
In other words: your time travel device has to be perfect in calculating where in the universe to place you, not just when. And if you do not get this absolutely correct, the earth, and in fact the rest of the universe will not be in the same place as it was when you left the present. You might just pop in existence a month prior in the cold vacuum of space since the Earth isn’t where it was when you started a month in the future. And that would kind of suck.
This could provide an answer to the question of why, if time travel is ever invented, we haven’t been visited by beings from the future. Perhaps the reason is that no one has or will (ever) solve the spatial problem, and the universe is littered with time travelers adrift between the stars and galaxies, or stuck inside the regolith of the moon or other celestial body.