Why Time Travel Won't Work (Sometimes)

[davidhorman]

Perhaps going back and kicking dad in the nuts is exactly the event which caused you to be born in the first place, and not the other kid. I like to think that's it how it would work, anyway - that's the way things were and that's how they will always be. Even if you try and kill an ancestor, you would fail (for whatever reason). It does sound a bit like something conspiring to maintain the timeline, but perhaps it's only the same kind of thing that "conspires" to draw massive objects together.

Yes, I do have a Star Trek script in my head waiting to be written. Shame all the good ones have finished their run.

David

 

[richardm]

It seems likely to me that if a time-travel machine was ever invented, it would be (a) very expensive and (b) tightly controlled.

It could very well be that there were observers from the future at the atom bomb tests or various other important points in history, but they'd be well trained to blend in seamlessly. And you'd only need to do it once, or maybe twice.

Besides, for most historians it would be much less interesting to do that than to go and hang around ordinary people and ordinary events - those are the things for which records are sketchy, and it would be genuinely interesting to be able to "go back" and have a shufti. And again, you'd be one or two people nipping in and out of the past, and being well-trained. Not just your average tourist, in other words.

Certainly, it seems highly unlikely that anyone would be allowed to go back and start killing people! Although since that person would already have been killed in the history of the people who went back and killed him, then ...
... This is the point where smoke starts coming out of the back of the computer, and a metallic voice says "Does not compute! Does not compute!", right?

 

[Wile E. Coyote]

First, according to Star Trek, accidental time travel happens about once or twice a year. This kind of thing always gets the crew in some wacky situation.

Second, I find it odd that everyone seems to worry about people going back in time to kill ancestors. Sometimes I think they would be more likely to go back an knock off a couple of in-laws ...

I think the only backward time travel theory currently considered plausible is the one where a traveller can only go back in time as far the the point at which the time travel machine he is using was turned on. This would be some sort of wormhole thingy.

Of course, this is a horrible idea, because you would then have hundreds of people from the future streaming through the instant you turned it on.

 

[Mark]

Interesting psychological study: Why do all builders of time machines seem to hate their fathers and grandfathers so much?

What, suddenly killing your grandmother is off limits?

 

[kedo1981]

Here is an even simpler reason why time travel into the past is impossible; time does not exist, it is merely a label the human mind places on the order of events as they move through space.

 

[Sundog]

Here is an even simpler reason why time travel into the past is impossible; time does not exist, it is merely a label the human mind places on the order of events as they move through space.

Wow, that simplifies everything.

OK. How about order-of-event travel?

 

[TillEulenspiegel]

Cecil " I think the theory about "nature conspiring to make sure causality isn't broken" is a load of BS. It seems to presume some sort of supreme intelligence that watches everything all the time."
It's not conspiratorial at all, just one of the apparently unbreakable constraints of the universe we live in.

FTL is not conspiracy and requires no Omnipotent authority why do You think causality does?In fact the central thesis is accessible in plain English and is intuitive "Effect may not precede cause",not like QM which alto being counter-intuitive and having Gordian knots of logic, yet appears to describe the nature of our universe quite well.

 

[scribble]

Here is an even simpler reason why time travel into the past is impossible; time does not exist, it is merely a label the human mind places on the order of events as they move through space.

Hrm... interesting contention.

Would you also say it's impossible to build a "space machine" because space is merely a label the human mind places on the location of events as they move through time?

 

[Walter Wayne]

I can't remember which really big name scientists said that time travel isn't a possibility as we have never run into any time travellers in our history. What he was saying was that if it was possible, we would already have known about it.

Made sense to me.

Not that I think time-travel is necessarily possible, but there is one flaw with that argument.

What if the time machine must be at both the source and destination of the travel? How does a time travel machine get you to a point where the time travel doesn't exist. It could be that time travel is only possible back to the point when the time machine is invented.

Walt

 

[scribble]

What if the time machine must be at both the source and destination of the travel?

That seems like a big "what if" - I mean, when I drive to Detroit, I don't have to call 'em up first to be sure they've got a car, too, do I?

You're picturing something like a star-trek teleporter no doubt. Why couldn't a time machine be more like a car, hop in and go?

 

[Archangel]

Originally posted by Walter Wayne
What if the time machine must be at both the source and destination of the travel? How does a time travel machine get you to a point where the time travel doesn't exist. It could be that time travel is only possible back to the point when the time machine is invented.

Assuming that Time Travel is possible, it is probable that this will be the first(*) type that is invented, however once we have a time machine that works like this perfected of course we would try to build a T.A.R.D.I.S. style machine.

*Assuming that we dont want to count conventional rockets, sattelites and future spacecraft as time machines because of relativistic time travel.

 

[Mark]

Hrm... interesting contention.

Would you also say it's impossible to build a "space machine" because space is merely a label the human mind places on the location of events as they move through time?

But time as we perceive it is strictly a local phenomenon. At a quantum level, it doesn't exist at all...all "nows" are simultaneous.

 

[scribble]

But time as we perceive it is strictly a local phenomenon. At a quantum level, it doesn't exist at all...all "nows" are simultaneous.

It's not possible to differentiate T for T+1 when examining a quantum event? How would you know when the experiemnt was done?

 

[(S)]

Not that I think time-travel is necessarily possible, but there is one flaw with that argument.

What if the time machine must be at both the source and destination of the travel? How does a time travel machine get you to a point where the time travel doesn't exist. It could be that time travel is only possible back to the point when the time machine is invented.

Walt

This will make it readily apparent when you succeed in building a time machine: A gajillion people will suddenly burst through, wanting to buy all the stock they can.

 

[Mark]

It's not possible to differentiate T for T+1 when examining a quantum event? How would you know when the experiemnt was done?

Well, you are looking at 2 different things: at a quantum level, the experiment (if it ever happens) is already completed.

I was specifically addressing your---I think erroneous---assumption that time cannot be a local event/perception, because then macro "space" must be as well.

 

[CrossHair]

Time travel

Here is an even simpler reason why time travel into the past is impossible; time does not exist, it is merely a label the human mind places on the order of events as they move through space.

I totally agree, however.... We observe time through our senses and by looking at distant gallaxies we percieve them as they were perhaps thousands or millions or billions of years ago. Therefore we are traveling back through time, not physically but still with one of our senses.

To physically travel through time would have to be in a space ship for this reason.... The earth and solar system are always in motion and we are not in the same location we used to be. To travel back in time from our present location would put us, most likely, into deep space because the earth and solar system are not here in the past. Therefore you had better be in a space ship to survive!

 

[Walter Wayne]

That seems like a big "what if" - I mean, when I drive to Detroit, I don't have to call 'em up first to be sure they've got a car, too, do I?

You're picturing something like a star-trek teleporter no doubt. Why couldn't a time machine be more like a car, hop in and go?

Yes but you know that detroit has roads. And yes it is a big what if, but time travel is pretty much a big what if.

 

[Cecil]

Cecil " I think the theory about "nature conspiring to make sure causality isn't broken" is a load of BS. It seems to presume some sort of supreme intelligence that watches everything all the time."
It's not conspiratorial at all, just one of the apparently unbreakable constraints of the universe we live in.

FTL is not conspiracy and requires no Omnipotent authority why do You think causality does?In fact the central thesis is accessible in plain English and is intuitive "Effect may not precede cause",not like QM which alto being counter-intuitive and having Gordian knots of logic, yet appears to describe the nature of our universe quite well.

Sorry for not being clear enough. The conspiratorial argument I was talking about was the one that goes something like, "I can travel back in time, but if I try to kill my grandfather the gun won't fire or I won't be able to get near him or he'll survive the 100-story fall, etc". I realize it's proposed because if you WERE able to kill him then you wouldn't have been born, so therefore your grandfather couldn't have died.

The flaw is that by travelling back to 1940 (eg) events which happened in 1980, like your birth, HAVE NOT HAPPENED anymore.

An analogy I like is that time is like a videotape that gets recorded as time passes. The tape is read-only before the current location and write-only after the current location. We have found the fastforward button (relativistic travel) but not the rewind button. If you jump back in time, it's like rewinding the videotape back and "starting over" from that point. Events which happened in the old timeline are not accessible anymore since the tape is write-only. If you then jump forward, you arrive where you started, but in the new timeline.

 

[ADD Boy]

Re: Time travel

I totally agree, however.... We observe time through our senses and by looking at distant gallaxies we percieve them as they were perhaps thousands or millions or billions of years ago. Therefore we are traveling back through time, not physically but still with one of our senses.

To physically travel through time would have to be in a space ship for this reason.... The earth and solar system are always in motion and we are not in the same location we used to be. To travel back in time from our present location would put us, most likely, into deep space because the earth and solar system are not here in the past. Therefore you had better be in a space ship to survive!

From what I read in "A Brief History of Time," I think a wormhole can tunnel through both space and time. So it's entirely possible to make the wormhole tunnel anywhere in time and space.

 

[iain]

Re: Re: Time travel

From what I read in "A Brief History of Time," I think a wormhole can tunnel through both space and time. So it's entirely possible to make the wormhole tunnel anywhere in time and space.

Big jump there. Just because a wormhole can tunnel through time and space does not mean that it is possible to make one that does. Making a wormhole may require more energy and better technology than the human race is ever able to harness, not to mention getting through it in one piece could be a challenge.