Time Travel: Possible or Impossible?

Great Debates
101

Well, not necessarily. Of course these and other paradoxes are why people assume there just has to be something preventing time travel even if as things stand we do not know how it is prevented.

Nevertheless, you can come up with possible answers to your problem.

For one you could assume we live in a multi-verse (which is a supported, albeit not popular, interpretation of Quantum Mechanics). In short there is a universe where you have a tuna sandwich and another Spaghetti-O’s and another a PB&J and so on. Free will is preserved. Which you choose to do just throws you on that new world line (and you are time traveling not in time but between different universes).

For another, and this one will hurt your head, while you have free will you will always “remember” what you do.

For instance, you go back in time and say “Blah blah blah” to your past self. The future you will remember saying that so you decide to go back and say “Yadda yadda yadda”. Thing is the future you will now instantly (and with no clue otherwise) remember that you said “Yadda yadda yadda” to your past self. In short whatever you choose to do is what you will remember doing.

Works the other way too. You travel forward and see the tuna-eating you. So you decide to have Spaghetti-O’s instead. So now you will remember seeing you eating Spaghetti-O’s. Again you have free will but whatever you choose to do is what you will remember doing.

Ack…I think I just popped a blood vessel pondering the implications of that. :cool:

102

So, if I go back to April 1997 and bet heavily on the Florida Marlins to win the World Series, I might get screwed if I land in the wrong universe? Dang, there goes my big plan. :slight_smile:

But if there’s a different universe to accomodate every meal choice I may make, and presumably every bit of minutiae in everybody’s life that has ever existed, there must be an inconceivably vast number of universes, most of which probably look nothing at all like ours given every divergent possibility. I could very well end up someplace where ther are no Florida Marlins, or Spaghetti-O’s, or Me, for that matter.

I think I understand what you’re saying here, but I don’t quite grasp how this would work; i.e., how opening a can of Franco-American would actually pysically alter my brain pathways.

Though, I guess none of this addresses the OP about whether time travel is possible… It just addresses the question of whether or not I’m smart enough to understand it. (There’s a 2-letter answer to that.:confused:)

103

Not denying the existence of time, just the notion that time is a physical thing. Seconds, minutes and hours do not measure time, they are increments of time, used to measure events.

Inches, feet, and miles measure the physical world.

Now, we’re entering the realm of theory.

Therefore, there is no need to imagine an additional dimension. The physical world allows for motion.

Whether the plane moves or not is irrelevant to the passing of time. The passing of time is occuring regardless if the plane is stationary or in motion. The interval of the plane’s movement from point A to point B is measured in increments of time, for information purposes. The measuring of the interval of point A to point B is time. Divide the time into the distance, and you get speed, another form of measurement that has effects in the physical world. A bullet traveling at 1000 fps hurts more than a bullet traveling at 100 fps. Speed, like time, is another manmade construct used for the purpose of measurement. It is a by-product of physical properties of mass, motion, distance, and the “time” it took to get there.

104

Yep. That is exactly what it is saying. That there are essentially an infinite (or astonishingly huge number) of universes out there. Basically, everything that can happen has happened…somewhere. It is mind boggling I know but real scientists have considered and developed the idea at length. While not testable (lots of these things aren’t) it remains a viable interpretation of QM even today. Some aspects of QM suggest this is what is happening. Of course the implications are so astounding that lots of people have trouble swallowing it which is completely understandable.

Well, if history is re-written then everything forward of that is affected too. We could suppose that some time traveler went back in time and made some change that allowed you to be born. You could have winked into existence 10 seconds ago and you and no one else would ever know the difference. It is not magically altering your brain pathways. It is altering history itself such that your brain pathways developed in the manner that makes you remember whatever it is you are remembering.

So, you go back and say “blah blah blah”. As you move into the future you will remember that. You decide to muck things up and go say “yadda, yadda, yadda” to yourself. Except as soon as you do that your “present” self will remember you said “yadda yadda yadda” and move forward in time with that memory. When you go back you will remember whatever it is you said, no matter how many times you choose to say something different.

105

You are answering yourself. It is right there in the bottom of your post.

You are measuring feet per second. Note it is inextricably linked in the notation. You cannot measure speed or motion without the time component. Spacetime…they are linked, intertwined, inextricable from each other (at least in this universe).

The units used are of course arbitrary. Could be miles per hour or kilometers per week or cubits per nanosecond or whatever. Nevertheless they are both necessary measurements to have a meaningful answer. They are both “real” things.

106

Suppose I show up (by snagging a convenient wormhole) in 2007. I confront myseld-now there are two Ralph 124cs-where does the extra mass come from?
And, perceiving a(electromagnetic) signal from the past would also violate conservation of charge.
So, I don’t see time travel as possible.

107

Well, space and time are inextricably linked as has been noted. If the universe does not care “where” a mass is why should it care “when” a mass is? You have just changed the coordinates of the mass and the total mass/energy of the universe remains unaffected if you look at it in its totality from past to future.

108

Yes, they are intertwined if someone wants to measure “speed”, but nature doesn’t care about measuring speed. Only mankind has an interest in knowing speed, and mankind created a method of computing speed.

109

By this token, it can also then be argued that if I went back in time and killed Hitler I would be saving exactly no one. Perhaps I would be creating a new universe wherein the Nazi party never rose to power and the Holocaust never occured. But back here in this old universe, well, it all still happened.

Bummer.

110

Yep (although whether you cause that new universe to pop into existence by “time traveling” or if time travel is just a means to move to a universe where you killed Hitler is open to debate).

More fun to ponder, if there is a multi-verse, is finding the world line where you are God King Emperor and all bow to your will (note there would be one for you and one for me and so on). :wink:

111

::sigh::

Nature does care about speed. As noted the faster you go the slower time moves (and the more compressed things become). This is a fundamental feature of nature and it has been proved experimentally…repeatedly. The speed of light is an absolute limit. So, nature obviously does take into account speed as a fundamental feature of the universe.

112

how do seconds, minutes, and hours not measure time? Are you saying that time doesn’t flow unless there’s an “event” to be measured? Is there no such thing as length unless there’s an object to be measured? Is length a mental construct of the human mind as well?

There’s no need to imagine it because the additional dimension exists. The very phrase “the physical world allows for motion” can be reduced to “the physical world allows for things crossing distances over a period of time”, which implies the existence of both distance and time.

again, you’re making the argument for me. you’re admitting to the physical property of motion, and yet you’re denying the legitimacy of time. The actual unit “second” or “minute” or “hour” is a human construct for measurement but I’m baffled at how you can claim that the thing they’re measuring is also a human construct that has no place in the natural realm. Speed is a byproduct of distance and time, which can easily be proven through dimensional analysis. Those basic DIMENSIONS of distance and time are inherent to all objects - stationary or not. A stationary object is just a special case scenario where the change in distance happens to be 0 over a period fo time. Speed is a property of the object, it describes the object, and it exists whether or not some scientist comes by and measures it or not.

113

They are manmade increments used to measure events. The sum of the equation is what is called the “time”.

Give me an instance of time without an event. A second? That’s 1/86,400th of a day.

Like Heaven? Must be, because a plane flying from point A and arriving at point B, regardless of how long it took, is still in the same dimension, just at a different location.

114

Hmmm… kinda like religion.

115

No, not really. At least this stuff has been subjected to scientific rigor even if it does sound like science fiction. Religion is just made up, cuz someone said so, stuff.

116

It’s in two different locations at the same time?

No, of course not - there is a pairing of times and locations, with one time per location. And as the plain moved smoothly from point A to point B, it smoothly moved from Time A to Time B as well. (Time A being the time it was when the plane was at point A, that is, and so on.)

So, clearly, the act of something moving through spatial dimensions unavoidably demonstrates movement through a time dimension as well. Obviously.

117

Time being a dimension is made more apparent with special relativity and space-time diagrams.

Every particle moves through spacetime at c. If I’m standing still and not moving through space, I am moving through time at c. A photon or any other massless particle moves through space at c, and therefore has zero time velocity.

Anything in between, and it’s some combination of the two. If I start from rest and go really fast, I take some of my velocity in the time direction and apply it toward velocity in the space direction, so that while I have increased my movement through space, I have decreased my movement through time (time slows down for fast-moving objects). But all in all, my speed through spacetime is always c.

118

Would that be Eastern Standard Time or Mountain Time?

119

No, nature cares about motion. Speed is what man has created as a way to measure an aspect of motion.

It depends on the perspective. The one in motion notices no discernable difference in his timeframe, as everything has appeared to slow due to the the laws of motion.

Or the more compressed things appear due to a doppler effect of light. An object moving toward an observer appears to compress, due to the compression of the light rays. As the object passes and moves away from the observer, the object appears to enlongate due to the stretching of the light rays. Like the doppler effect of sound. As a train blowing it’s whistle on approach to an observer, the observer hears a higher pitch due to the speed of the train compressing the sound wave. As the train passes and moves away from the observer, the observer hears a lower pitch of the whistle due to the stretching of the sound wave.

Now, let’s take two astronauts on a space-station. One takes their vehicle on a little spin, say some orbits of 93 million miles, traveling as 1/2 lightspeed, which would take the vehicle @ 1 sec to orbit the space-station.

The astronaut that remained on the station observes his partners joyride on radar and observes 1 sec for each orbit. After 3,600 orbits, his buddy re-docks at the space station. The astronaut that remained on the station commented, “Well, you did 3,600 orbits, and it took you an hour.”

The astronaut who took the joyride said, “No, I was only gone 45min.”

Time did not slow down, the physical effects of the motion caused the astronaut’s perspective of time to slow down. If his 3,600 orbits only took 45min. , then he was traveling faster than 1/2 lightspeed, but this was not observed by his partner monitoring the orbits on radar.

120

how about… it’s be 400 seconds since the last event? you’re stating that if there is no event, time doesn’t exist. then following that logic, does length cease to exist if there’s nothing to measure?

Then you go on to attack how time is relative. Nobody is doubting the relativistic effects of time especially with velocities approaching c. in fact some have used it as an argument of relative time travel pertaining to the OP. However, how does saying that time isn’t constant detract from the fact that time exists? wouldn’t the fact that time can be affected by motion the same as length is affected by motion help in the case of time’s natural existence and not just a mere figment of human imagination?

it sounds like you’ve backed yourself into an argumentative corner, and should drop the argument. if not, i’d like to hear an actual feasible reason of why time is just a human construct and it doesn’t exist in the natural world.

you can start by explaining how using speed to measure motion rejects the existence of time: