Time Travel Looks To Be Possible.

[kronin323]

Explaining it to another person is another matter entirely

You've got that right - I consistently fail, and don't think I did much better this time around (and that was just barely touching the basics...) But I still keep trying...

 

[WavecloudCustoms]

I see general relativity in action everywhere..

One example - You're trying to turn onto a fast moving road at a T junction. A Ferrari is coming along at 150 with, say, 100 meters between you and the oncoming Ferrari. On another instance it may be a bus coming along at 50 with 25 meters between you and the bus....

Guess which I would rather pull out in front of...?



Although the buss looks closer (is closer in 3d), it's actually further away than the Ferrari in 4D..

 

[kronin323]

I see general relativity in action everywhere..

One example - You're trying to turn onto a fast moving road at a T junction. A Ferrari is coming along at 150 with, say, 100 meters between you and the oncoming Ferrari. On another instance it may be a bus coming along at 50 with 25 meters between you and the bus....

Guess which I would rather pull out in front of...?



Although the buss looks closer (is closer in 3d), it's actually further away than the Ferrari in 4D..

With all due respect, that example isn't about general relativity (which is Einstein's theory of gravity). It's not really even an example of special relativity - the speed difference isn't big enough to experience relativistic effects, and a good example of special relativity should need the perspective of more than one observer... really it's just classical physics with a little mind-playing-tricks-on-you thrown in.

(Sorry, not trying to be a d!ck - from your other posts I respect you a lot (and envy how much time you get to spend outdoors living the good life); please don't take offense. It's just that with science I choose to put truth before courtesy...)

But here's a nice little mind-twister regarding general relativity:

When you're in your car and you step on the gas, you feel yourself being pressed back in the seat from the acceleration. But once you get up to speed and stop accelerating, that pressure goes away.

When simulating weightlessness / freefall, there's a plane where they take you up and down, up and down. On the down legs you achieve terminal velocity, which means you're falling as fast as gravity can pull you, it can't pull you any faster, and you feel weightless. (That doesn't work with skydiving because of the wind resistance, but in the plane, it takes the wind resistance and has the propulsion to overcome it and achieve terminal velocity).

When you're standing still on the ground, though, you feel pressure through your feet from gravity's pull, the solidity of the ground being the only thing preventing you from being sucked in.

In general relativity, that force you feel when you're accelerating and the force you feel from gravity's pull when standing still on the ground? They're the same thing. General relativity does not differentiate the two.

Really, when you're in free fall, falling at terminal velocity as fast as gravity can pull you, that's the only time you aren't accelerating. You may be in motion, but you're just following the shape of the fabric of spacetime, warped by the gravity well caused by the mass of Earth (remember those old representations of spacetime as a grid with planets and suns etc dimpling down that grid like a bowling ball on a soft bed?)

Since the ground prevents us from continuing down the gravity well and following the local shape of spacetime, the resistance creates a force that, within the context of general relativity, is identical to acceleration.

So, within the context of general relativity, we spend our entire lives in a state of acceleration, even while standing still...

 

[Ralph Marshall]

You've got that right - I consistently fail, and don't think I did much better this time around (and that was just barely touching the basics...) But I still keep trying...

I actually think you are doing a great job explaining compared to much of what I have read on the subject. I need to check out The Elegant Universe. It can't be much more difficult to follow than much of the post-modernist fiction that I have recently been reading!

 

[WavecloudCustoms]

(Sorry, not trying to be a d!ck - from your other posts I respect you a lot (and envy how much time you get to spend outdoors living the good life); please don't take offense. It's just that with science I choose to put truth before courtesy...)

Hey - no worries

I guess my outlook is a bit surfedelic!

Heres another simplistic idea.. ?

My watch, whilst sitting flat on a table, the very end of the second hand 'sweeps' around making a perfect circle.... If I pick the watch up a few inches above the table, the end of the sweeping hand is no longer making a circle, its making a spiral. That means that, just by moving the watch I have made time a bit longer.... ?

 

[headpatrolman]

I am soooooo confused. I once dropped a pair of glasses and in my mind time slowed down as I watched them seemingly in slow motion hit the ground lenses down and screw them all to hell.

Nooooooooooooooooooooooooooooooooooo!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[kronin323]

I actually think you are doing a great job explaining compared to much of what I have read on the subject. I need to check out The Elegant Universe. It can't be much more difficult to follow than much of the post-modernist fiction that I have recently been reading!

Thanks - posting something like this here, I have to wonder how many people are reading it and wishing the forum had a "dislike" button...

It can be useful for travel, though - if I've got some chatty DB next to me on the plane who just won't take a hint, I can say, "OK, you want to talk, let's talk. But I get to pick the subject. And my subject is... physics!"

Either he shuts up or I get to talk about physics. Win-win.

 

[kronin323]

I am soooooo confused. I once dropped a pair of glasses and in my mind time slowed down as I watched them seemingly in slow motion hit the ground lenses down and screw them all to hell.

Nooooooooooooooooooooooooooooooooooo!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

lol!

 

[kronin323]

Hey - no worries

I guess my outlook is a bit surfedelic!

Heres another simplistic idea.. ?

My watch, whilst sitting flat on a table, the very end of the second hand 'sweeps' around making a perfect circle.... If I pick the watch up a few inches above the table, the end of the sweeping hand is no longer making a circle, its making a spiral. That means that, just by moving the watch I have made time a bit longer.... ?

That's good - as a literal example, no, just moving the watch a few inches doesn't create relativistic effects. And remember, you need more than one observer with different perspectives to properly illustrate it.

But as an analogy for how a fixed speed of light makes time a variable, it is perfect:

So let's say the very end of your second hand is a photon (particle of light) spinning around the watch at the speed of light. When you lift up the watch, one observer lifts up with it while a second observer stays relative to the table.

From the perspective of the first observer, the photon is just spinning in circles. But from the perspective of the second observer, the photon is traveling a spiral, which is a longer path.

But if the speed of light is fixed, how can that be? How can it go a longer distance for the second observer than it did for the first observer in the same number of revolutions, traveling at a fixed speed?

The answer is that time moved at different speeds for each observer. Within each observer's own perspective, time moved at a normal pace. But between the two observers, time moved more slowly for the first observer (the one who lifted with the watch) than it did for the second observer.

With special relativity, there is no master, overall, "correct" perspective. Each observer's perspective is equally valid. The only way that two observers watching the same photon traveling at a fixed speed can have it travel further for one observer than the other is for them to travel through time at different rates.

And it fits with the earlier post, where we are all traveling at the same total speed through the four spacetime dimensions, just distributing that total speed differently. The observer who lifted with the watch added more speed to travel through a space dimension, which removed some speed through the temporal dimension, so time moved more slowly for him than for the other observer.

 

[Ralph Marshall]

Ok, so I am more than a little out of my league here. Stupid question, but when you say time "moved" at different speeds for the different observers - does time actually move? I am certainly not up to date, but a good while back, I seem to remember that there were several different schools on the concept of time (which I am sure there still are and always will be). Is time linear, as in straight line? Is time cyclical, repeating? I have heard it described as spiral, too. Though we tend to view time as a measuring stick, time is actually much more abstract and complicated. I have heard it theorized that all time actually exists simultaneously - past, present, future. I can't even begin to get my head around that! That to me is up there with trying to imagine nothingness or infinity - simply impossible to fathom.
And as far as quantum mechanics are concerned, we haven't even scratched the surface - parallel dimensions and multiverses and the like...