Time travel is easier than that

Cecil's Columns/Staff Reports
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I’m sure you knew this, but according to Einstein’s special theory of relativity, we can travel into the future with conventional technology, provided we can somehow accelerate to close to the speed of light.

Time dilation ( t = to*sqrt(1-v^2/c^2) says that time we notice while traveling close to the speed of light is very slow compared to Earth reference, if we were at 0.99999c, about 223 years would pass in one year.

We could just build a ship that can accelerate that fast, wait a while, turn around, and come back to a new world. Small task? No, but it is possible.

So instead of going into the past, which would lead to poor medicine and perhaps the destruction of all human life (from improved super bacteria), check out the future so you can get killed by their newer, improved super viruses. Less damage done that way.

df

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Looks like a contradiction to me.

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It is preferred, (and easier for the reader), to include a link to the column being discussed.

Is time travel possible? (02-Jun-1989)

Quand les talons claquent, l’esprit se vide.
Maréchal Lyautey

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Why does Larry Niven’s “A World Out of Time” come to mind?

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Cecil wants to know, if time travel’s possible, why haven’t people from the future visted us? The same question occurred to Stephen Hawking. My answer: The human race goes extinct before we learn how to travel into the past.

Maybe on 1-1-2000? :slight_smile:

>< DARWIN >
__L___L

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hussman writes:

You’re overlooking the obvious man… you’re travelling into the future right now, without even approaching the speed of light.

What special relativity really says is that two observers travelling at different velocities will observe time differently.

Ahhh… Now you’re talking about travelling backward in time. To do this using the equations of special relativity you have to move faster than the speed of light. I won’t even go into all the problems with this approach.

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Read “Future Magic” by Robert Forward. In it, he describes many ways in which time travel is possible under Einsteinian physics. Most of them revolve (ha ha) around this idea. Take a huge mass. Really really really huge. Rotate it. Rotate it really fast, so at the surface of it, you have huge masses going at significant fractions of light speed. As we all know, that leads to many interesting effects, not the least of which is the mixing of the spacial and time dimensions. Under certain circumastances, it is then possible to go back in time.

Yes, this is wwwaaayyy past current technology. However, nothing forbids it theoretically.

(Robert Forward is a very um… adventureous thinker, but not a nut. He works at JPL and has many patents, he is a respected mainstream scientist.)

Also, if you believe in “white holes”, then the possibility can arise. Similar to the above reasoning, black holes mess around with the time and space dimensions, so if you can only come up with a way out of the black hole (assuming you somehow survived the trip in!), you might be able to figure something out.

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If it were possible to travel into the past, why aren’t we now plagued with tourists from the future? At the very least, it seems like we would have at least one example of someone who had done it! (See, it’s easy to figure this one out, and it doesn’t even take an advanced degree in physics!) Travel into the future is a much simpler problem, though. If we can ever figure out a method for suspended animation (which shouldn’t be beyond the reach of science), then we will, for all practical purposes, have invented time travel into the future. It’s a one-way trip, though!

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kidbrad writes:

Ummm… No. Space compresses and time dialates (relatively speaking), but they don’t mix. If you were able to achieve light speed (which you couldn’t, but let’s pretend) time would effectively slow to a halt and distance would compress in your direction of travel such that distance would have no meaning (but then, what’s distance without time anyway).

Not within the framework of “Einsteinian physics” (as you put it). To make the equations work to produce negative time, you have to have a velocity greater than light speed… but you can never reach light speed in the first place because as you approach light speed, it takes greater and greater amounts of energy to increase your velocity and nearly all of the energy applied goes into increasing mass.
I’ve not read Robert Forward’s “Future Magic” (which is more than 10 years old) or his updated version, “Indistinguishable From Magic”, but I suspect that you have either misstated his theories; or he has revamped his theories; or he is, in fact, a nut! [wink]

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kidbrad writes:

JoeyBlades replies:

Ummmm…Yes. According to General Relativity notes:
Lorentz transformations fall into a number of categories. First there are the conventional
rotations, such as a rotation in the x-y plane: [matrix deleted]
There are also boosts, which may be thought of as “rotations between space and time directions”.
**oosts correspond to changing coordinates
by moving to a frame which travels at a constant velocity.

Note: Lorentz transformations are the special relativity version of translating between coordinate systems (like between rectangular and polar). They are special because the “distance” between two spacetime points does not change under these transformations.

TheDude

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getting back to worm-holes, with the “tunnel through the apple” analogy, is cecil implying that time is cyclic? or, is he implying that it has a curvature to it, although it has other dimensions of movement so that it is at least “cylindrical”? if it is cylindrical, though, on at least one dimension it is then cyclic. so, then it has some sort of “periodic” element. i wonder what one “period” would be then, or the length thereof…

“I play the fool, Pyotr Alexandrovitch, to make myself agreeable.”
–Fyodor Pavlovitch, Brothers Karamazov

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but anyway, cylindrical with respect to what?
it is so strange talking about these the “shape” of time since it seems that everything is with respect to time, so that time is “the first axis” of anything. but, anyway, i am delirious now. gotta start getting ready for final tomorrow.

“I play the fool, Pyotr Alexandrovitch, to make myself agreeable.”
–Fyodor Pavlovitch, Brothers Karamazov

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I met Robert Forward about 10 years ago. He bought me a drink. In my book, he can’t possibly be a nut.

I once lost my corkscrew and had to live on food and water for several days
(W.C. Fields)

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It’s not Forward’s personal theory anyway; he just wrote about it in his book. It was formally presented in a for-real physics paper called “Rotating Cylinders and the Possibility of Global Causality Violation”, and it’s taken entirely seriously.

However, it is only proven that it will work if the rotating cylinder is infinitely long. It is thought that it will work if it is merely very long, but not, the last I heard, proven.

Also, the rotating-cylinder time machine cannot take you back to a time before the machine was built and started.

By the way, going faster than light will not take you into the past. There’s a square root in the equation, so the number doesn’t go negative, it goes imaginary.

As to the absense of time travellers, one might consider Niven’s theorem: If a time machine is invented, sooner or later somebody will use it to prevent it from being invented. Therefore, eventually, all time machines are uninvented and the timestream settles down to a stable state.

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

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Contradiction? If you count propulsion as conventional technology, then future travel is possible.

How to make the spacecraft or inhabitants survive that speed (especially since a pebble would punch a hole through the vessel) remains to be determined, but it’s still only (I use it sarcastically) an engineering problem, not a scientific impossibility.

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TheDude writes:

Boosts do not blur the distinction between spacial dimensions and time, which is what kilbrad implied by “mixing of the spacial and time dimensions”.
Colin Wilkinson wrote:

I don’t believe he’s a nut either. His credentials look pretty solid. I was really trying to imply that kilbrad was likely misrepresenting the theory. In fact, my understanding of the theory of “Global Causality Violation” is that it requires that the Tipler Cylinder be enormously massive so as to warp space-time, similar to the density of a black hole, except wrapping space-time around the cylinder like a giant roll of toilet paper. You can guess, from my analogy, what I think of this theory…
John W. Kennedy wrote:

I think Frank Tipler first conceived of this theory.

Taken seriously by some - not taken seriously by others. It requires that the gravity be sufficient to warp space-time, yet somehow not collapse the cylinder length-wise…

Proven mathematically feasible, not experimentally so.

True. Imaginary quantities have their place in the real world, but I have not been arguing the case FOR FTL travel anyway, so I won’t quibble over an imaginary quantity here or an infinite quantity there…

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You know, we’re overlooking another very practical reason that we’re not plagued by tourists from the future.

WE (the earth, sun, solar system, galaxy) are MOVING REALLY FAST.

It always bugged me that HG Wells missed this point in his book as well as every other author I’m aware of. If you were to ‘beam out’ of time and go backwards you would then ‘reappear’ in time where you left, which would be in a place the earth is today but WASN’T yesterday. You’d then have to trek many miles through empty space to ‘go back’ to where the earth was in history.

To imagine this another way, the earth is rotating at about 720 miles per hour average.

(e.g. rough numbers 7926 mile diameter*(pi=3.141)/24 hour day=1036 mph but I’m not on the equator, I’m around SF California so I’m interpolating it’s about 720 or so…like I said… FAST)

Now imagine you beam back in time 10 seconds. You’d be displaced 2miles! And thats just in relation to the surface of the earth!

Then you have the rotation of the planet around the Sun. Let’s assume it’s a perfect circle (please) so the approximate speed around the Sun would be:

2x(radius=AU=~93,000,000 miles)xPi(3.141)/365days (or 8760 hours)= ~65000 mph or in that 10second backtrack…180 miles off the surface of the earth.

Then you have the motion of the solar system in the galaxy AND the motion of the galaxy ‘out’ from the big-bang and well… I think you get the picture.

It might be fun to figure out a ‘real’ distance per second but then you’d have to account for the 186million mile arc of the orbit of the earth and such… and what good would it be anyway but, it’d be interesting.

Given that small variations in mass and energy (cosmicly speaking) can affect trajectories, I wonder if predicting the relative position of the earch relative to time in the past is even possible. It might be a paradox in that if you were to spend the energy and project a ‘mass’ back through time that it might affect the trajectory of the earth enough so as to not put you where you are today and thus make a paradox in that you couldn’t really say where the earth was. Kind of a 4th dimensional quantum uncertainty principle.

Time travel is cool.

-UnderDog

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I still like the “Back to the Future” flicks. And I’m still working on the DeLorean in the shed out back…

You just wait! (Or should you just remember?)

I don’t know why fortune smiles on some and lets the rest go free…

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There was a short article in Sunday’s The Independent about time travel:

Oxford physicist says time travel is possible

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forget about the time machine, just take a nap-- ever have a dream come true? you were remembering the future. it may have been linear or spliced with other bits of your subconscious, but it was not just a deja vu brain fart.
there is also the consideration of societies which keep no linear time–any anthropologist/time theorists out there?