# Time travel applications

1. Aug 18, 2008

### epkid08

Two objects lie motionless in an isolated frame. One object accelerates to a speed v, then then holds that speed for an amount of time t. This causes the accelerated object to travel a time $$t_s$$ into the still motionless object's future.

$$v=\frac{c\sqrt{t_s^2+2t_st}}{(t_s+t)}$$

If you're wondering I defined $$t_s$$, time skipped into motionless object's future, equal to $$t_c-t_p$$, coordinate time minus proper time. Solve for coordinate time, and plug it into the time dilation equation. Then solve for v.

This seems like it would have multiple applications for various preserving/maturing things i.e. foods, alcohol in our world.

Has anyone seen this before? Is it correct? Is it applied in our world today?

Theoretically, if an object is motionless in a vacuum with 0 forces acting on it, does it experience time? Apparently, most people view time as a philosophical thing more than anything, but furthermore a consequence of motion. So my question is just that, is time just a consequence of motion?

2. Aug 18, 2008

### matheinste

Hello epkid08.

Can we be motionless in time as well as space?. I think we are always moving forwards in time. Time and space are united as spacetime and i think there is a condition that that our wordlines be always future directed.

Matheinste.

3. Aug 18, 2008

### epkid08

Heh, I was going to add in parenthesis that it's impossible to do so, but I didn't. I think my main question was is time truly just a consequence of motion, or is it a truly unique 'dimension' that applies to all space. I suppose both could very well could mean the same thing, it's just how someone thinks about it.

4. Aug 19, 2008

### epkid08

It doesn't seem like I explained things well enough because no one posted, so I will try again.

If we have the coordinate time of an object, $$t_c$$, and we have the proper time of an object, $$t_p$$, we can see that with a velocity of 0, they are the same. As the object accelerates, $$t_c$$ increases at a much higher rate than $$t_p$$. When the object decelerates back to 0, depending on the velocity and proper time, the object will see that the observer has aged a given amount of time more than the object did. We can define this extra time as 'time the object skipped into the observers future', $$t_s$$. Obviously, $$t_s$$ can be easily calculated by taking $$t_c-t_p$$. From here the variables can be rearranged in many various ways. I will solve for $$t_s$$ first, then for velocity.

$$t_s=t_c-t_p$$
$$t_c=t_s+t_p$$
$$t_p\gamma -t_p=t_s$$
$$t_p(\gamma -1)=t_s$$ (1)

$$\gamma =\frac{t_p+t_s}{t_p}$$
$$\sqrt{1-v^2/c^2}=\frac{t_p}{t_p+t_s}$$

Skipping some steps...
$$v=\frac{c\sqrt{t_s^2+2t_pt_s}}{(t_s+t_p)}$$ (2)

In words:
Two objects lie motionless in an isolated frame. One object accelerates to a speed v, then then holds that speed for an amount of time t_p. This causes the accelerated object to travel a time $$t_s$$ into the still motionless object's future.

I've never seen this derived version of relativity. It seems like this could be applied in multiple ways in our world.

Is the derivation correct? Is it applied in our world?

5. Aug 19, 2008

### MeJennifer

Sorry but that statement does not make any sense to me.

6. Aug 19, 2008

### epkid08

If an object travels at v>0, while its observer is stationary, the moving object will experience a slower rate of time than the still stationary observer. This change in time is shown by $$t_s$$. Whether or not you want to call it 'time travel' really makes no difference. Is there a better phrase for it?

7. Aug 19, 2008

### isly ilwott

I have difficulty believing that a motionless object does not experience time. I see no connection between the period of time in which an object exists and the distance it may or may not have traveled in that time period.

8. Aug 19, 2008

### MeJennifer

And how would you propose to determine who is traveling and who is stationary?
An object is only moving relative to another object.

9. Aug 19, 2008

### epkid08

Ahem, treat velocity as a vector.

10. Aug 19, 2008

### epkid08

If we define proper time strictly as a consequence of motion, then an object without motion (this will never happen), will also be without time.

11. Aug 19, 2008

### MeJennifer

A vector?

You and I are in empty space and we see that the distance between us is constantly changing, who is moving?

Where does your vector come in?

12. Aug 19, 2008

### isly ilwott

Quite so...if you define it that way. If I define black as white then all things white are actually black. Your definition is errant.

Also, your claim that an object without motion will never happen is errant. Once you have established a vantage point, anything that does not move in relation to it is without motion.

13. Aug 19, 2008

### isly ilwott

Whether treated as a vector or not, the reference point will determine which is moving.

Velocity in commonly treated as a vector. The magnitude of an object's speed coupled with the direction of travel yeilds the object's velocity. For both parameters, there must be a reference point.

14. Aug 19, 2008

### MeJennifer

Coordinate and frame wise yes, physically no. Physically they are simply moving with respect to each other.

15. Aug 19, 2008

### isly ilwott

The motion must be referenced to something

To a person on a speeding train, the dining car is not moving, but the track is. To a person standing on the track, the train is moving but the track is not. In order to determine the relative motion of any object, a reference point must be utilized.

16. Aug 19, 2008

### epkid08

At the begining of the topic I used that as the definition because it's a widely accepted view on it, I'm not even saying it's the right view of it, my intention was to get a better perspective on it.

There is no such thing as a true isolated frame, gravity will always be there, and thus there will always be a real force acting on an object.

Are you saying it is impossible to observe a 'left' and a 'right'? If the object is traveling relative to the observer, the object is traveling at v; if the observer is traveling relative to the object, the observer is traveling at -v.

It was not directed to you.

There doesn't need to be a reference point, as I said before if the object is moving relative to the observer, the object is traveling at v, if the observer is moving relative to the object, the observer is traveling at -v. This is because the object can distinguish the x coordinate relative to observer, and vice-versa.

17. Aug 19, 2008

### MeJennifer

Not true, in relativity motion is always relative. Don't mix up physical reality with frames and coordinate systems.

18. Aug 19, 2008

### isly ilwott

It seems a physical reality to me that in speaking of physical objects, the motion of any object must be measured in reference to something else, namely the reference point.

19. Aug 19, 2008

### epkid08

Are you saying that an object is never in motion if it doesn't have some type of reference? That's like saying, an object without light reflecting off of it is not there.

Although, if the universe was truly infinite in space, then I suppose you would need a reference point, but that's a different subject.

20. Aug 19, 2008

### isly ilwott

No. I'm saying that in order to measure the motion, there has to be a reference point.

I think that regardless of the limits on the volume of space involved, there has to be a reference point to quantify the motion (change in position of the moving object relative to the reference point).

21. Aug 19, 2008

### MeJennifer

Simply untrue.

If you and I are in empty space and we send light signals to each other we can easily determine the amount of motion between us. There would be no need for frames or coordinate systems just the relativistic doppler formula.

Last edited: Aug 19, 2008
22. Aug 19, 2008

### epkid08

Given that the universe is spatially finite, you will always know that traveling in a direction will cause motion.

Given that the universe is spatially infinite, you will not be able to distinguish, given no reference point, whether or not you hold a motion.

23. Aug 19, 2008

### peter0302

Sure. Remember though that accelerating something to relativistic speeds requires a LOT of energy! So wouldn't it be a lot cheaper to freeze the food than to slow down it's clock by sending it around the earth at .99c? :)

As for maturing things like alcohol - no, that's where you've lost me. You can slow the aging of something you send out at relativistic speeds. You can't accelerate its aging.

Most certainly it is not applied. The only real world application of time dilation I am aware of is in the GPS system which does have to account for it because of the required precision. But I've never heard of a practical application of slowing an object's aging.

Time is a consequence of change of any kind. Could the universe change in any wya if there was no motion? It is difficult to imagine it could. The fundamental particles don't change their properties without some kind of motion accompanying that change (i.e. an electron/positron can't become two photons without some kind of motion). So I'd have to say you're rigth, in your hypothetical there is no concept of time.

24. Aug 19, 2008

### epkid08

Space beer! I'm sure sending beer into space so it matures faster is very cheap and efficient!

25. Aug 19, 2008

### isly ilwott

But you are still measuring my motion relative to yourself. I am measuring your motion relative to myself. Each of us has a different reference point...our own position.