Does this argument against time travel exist...?

Space is a major issue. If you were to travel 10 minutes in time, forward or backward, you would be in outer space.The earth travels about 584,020,178 miles (939,889,369 km) in the course of its orbit about the sun. 16 million miles per day. 666 666 miles an hour. 11,111 miles per minute.

Yes, this point has been made, but it's a good one. It's usually expressed as "If we will some day invent time travel, why do we never see visitors from the future?"

You seem to have missed the intrinsic paradox of your version. If we someday invent time travel and bring it back into the past and spread it, there will be no need to invent it in the future, because it will "already" have been invented. But then it never gets invented.

Ray Bradbury has a good short story, "A Sound of Thunder" about this paradox. Time travellers visit the distant past but are careful not to do anything that will change the present. One is not careful enough, kills a small insect, and returns to a present that is an unpleasant parody of ours.

All that is visible must grow beyond itself...
http://www.cafepress.co.uk/ahua/8761658

If time travel were possible into the past, logically it would create an alternate reality and feed into the many worlds concept proposed by some scientists.

Requiescat in pace, Krystle Papile. I'll always miss you.

Way late to this thread but some food for thought.

i. Carl Sagan. Time travel is invented but the travelers keep themselves hidden from us for reasons we can only speculate.

ii. Carl Sagan. Time travel is invented but the nature of it means that travelers can only go back as far as when the machine/device/means was created. So if time travel is invented in 2100 we will never see future time travelers from beyond 2100.

iii. Carl Sagan. Time travel is possible but never invented. We die out as a species before then.

iv. Time travel to the past automatically creates a parallel timeline each and every time it is used. So, if time travelers from the year 2100 travel back to 1960, IN THAT INSTANT they create ANOTHER universe in which time travel is possible and where they do indeed create a utopian universe and live out their lives there.

In OUR universe though we never see them again once they leave for the past. (Hope that makes sense...) Time travel to the past is possible but we can never observe the results of it.

v. Pre-destination. Time is 'fixed' in a single timeline and everything is pre-ordained. Time travelers wind up being part of their own past, probably unintentionally. For example, travelers travel to hunt dinosaurs à la Ray Bradbury, accidentally release a virus that wipes out dinosaurs leading to mammals and mankin as it always was. Also means that free will is an illusion.

vi. The Looper model... which is quite clever but hard to explain. Time is a single timeline but any changes as a result of time travel ripple up and down the timeline in such a way to keep things consistent.

The nature of this model means that travelers can't change time so drastically that the time traveler no longer exists or has a reason to be in the past.

A time traveler could for example go back in time, travel to the other side of the planet and kill ten minor random people. Although it would change the future -- no descendants -- it's unlikely to affect the future in such a way that it affects the time traveler in any way. He had no memories of those people anyway and in no way does their lack of descendants affect the development of time travel or the birth of the time traveler in the future.

However, it wouldn't allow him to travel to the past and kill his grandfather before he was born. In that case a paradox would be created and this model allows for changes only up the point where paradoxes cannot be created.

vii. My own theory is that time travel via worm holes is possible, but some property of spacetime keeps them from forming in such a way to create a potential paradox.

For example, you create a 100-year wormhole. Fly into this end of it in 2015 and you emerge in the year 1915... but 100 light years from earth. Turn around in your time/spaceship and head back to earth at the fastest speed possible (speed of light) and you would get here just in time to see yourself disappearing into the wormhole the first time. (Well not quite... you'd be a few minutes late but you get the idea.)

And, no, you can't create TWO wormholes -- one away from earth and one toward earth -- to try to defeat the principle and travel back to earth 200 years ago.

It's based on the concept of the lightcone which you can Google to learn more about. I came up with the idea independently but some physicists proposed this idea in the 1990s.

The cool thing about this theory is that it means that there could be colonies of humankind already seeded among the stars RIGHT NOW but we will never know of them. Time travel via wormhole is invented in 2100. Our space/time travelers go back 100 years and emerge in the year 2000. BUT, they emerge near the star BD+42 550 in the constellation of Andromeda, 100 light years from earth.

They find an earth-like planet, establish a colony, send a signal to earth. That means that RIGHT NOW a distant earth colony has been established for 15 years already! But we won't get their signal for another 85 years. Cool concept, eh?

I like to think that time travel is possible in the future (probably far into the future). But I like to think if/when it's invented, it will be (or is) strictly controlled by some government agency, so we don't cause paradoxes or leak information to the past. And the resources needed to travel are probably (or probably be) very expensive/rare.

Think about airplanes. When we first invented them, it was no better than today's crop duster. You couldn't go very high. Since the pilot was not in a pressurized enclosure, the higher you went, the less oxygen you had so you'd eventually blackout (if the engine didn't stall first). Later, we invented the jet airplane. This could go higher and faster than any airplane we made before. The pilot was in a pressurized enclosure so he/she wouldnt blackout from the lack of oxygen when they were high above the ground. The jet was a solution all of our problems. Anyways, point being, we've had jet aircrafts around for years, everyone knows about them. But you cant exactly built one in your backyard. Even if you do manage to get the parts and assemble one, you need jet fuel, which is very expensive and difficult for a civilian to get their hands on. Even if you do get fuel, you need a large runway. Even if you have a runway ( or something close to it), you technically can't operate it without permission (and, I imagine, a permit and proper license) from the FAA.

So I think time travel will be like that. You will need special training and permits and stuff. It will be limited only to people with that training (part of it being a contract stating that you cannot go back in time and share knowledge of the future, or change major events from happening, or anything else that will cause a paradox). And I'm sure the machine will have a sort of "black box" like planes do, recording everything. And each inconsistency between the black box and the flight plan of each trip will be put under review and scrutinized. And if any "pilot" of the time machine is caught misusing the machine, they'll be banned from time travel indefinitely.

That's just what I can see happening.

Also... just think of the mess it would create with ALL these billions of future people coming back to attempt to alter the future. :) :)