# How long till we can travel into the future?

1. Jul 27, 2004

### Vast

Can someone please tell me how fast we would need to travel in order to go a relatively short distance into the future? Just a matter of years really…

2. Jul 27, 2004

### photon

We should be able to do this in about 14 years. I already went ahead and checked...

3. Jul 27, 2004

### Prometheus

There is only one speed in space-time, the speed of light. In this context, your question has no meaning.

In case you haven't noticed, you have been traveling into the future your entire life.

4. Jul 27, 2004

### Vast

Apparently we can do it now. :tongue2:

Well again we don’t need to travel at such a speed, experiments using two clocks; one on the ground and another in a plane have shown a slight difference. The faster you travel the slower time ticks. Therefore traveling at a relatively fast speed out in space, upon returning to earth time should have elapsed longer than it has for you…

5. Jul 27, 2004

### Prometheus

Think about what you have said here. You claim that we do not need to travel at such a speed, by which I assume that you mean the speed of light.

You then provide commonly used examples that contradict what you said.

Why does the increase in motion through space lead to a decrease in motion through time? Because the speed of light is constant in space-time, and all motion in space-time is at the same speed, the speed of light.

6. Jul 27, 2004

### Vast

http://www.astro.uu.nl/~strous/AA/en/antwoorden/relativiteit.html

7. Jul 27, 2004

### Prometheus

I consider your citation excellent, because it coincides very well with what I contend.

I am now confused, however, as to the purpose of your initial posting. Did you just come upon this web page, and therefore have a better understanding of what your were seeking, or what was your purpose of your initial post? Perhaps I misunderstood your purpose.

8. Jul 28, 2004

### Vast

Actually I think I do have a better understanding of what I was seeking, and correct me if I'm wrong...
If you want to travel any significant amount of time into the future you essentially have to reach a speed close to the speed of light?

9. Jul 28, 2004

### Prometheus

Correct.

Each of us is moving into the future, all of our lives. As well, we each move into the future at a somewhat different rate. However, the total difference over a life time is limited to years, due to the inability of people to vary sufficiently in their rate of motion through space relative to each other to gain extremely large differences in their rate of motion through time.

If a person would like to move a century or more into the future of the planet, for example, which is an entire life time, then much greater motion through space would be required. Motion near the speed of light increases this possibility.

Notice that the use of the phrase "speed of light" in the preceding paragraph and in your posting is confusing and misleading. There is only one speed in the universe, because everything always moves at the speed of light. The phrase as used here refers to the speed of light in a Newtonian sense, wherein the speed of light refers to motion through space only, and motion through time is ignored. Remember, the speed of light is constant in space-time, and is the only rate of motion in space-time. We are always moving through space-time at the speed of light. Motion through space and time are symmetrical. As we increase our rate of motion through space, there is a symmetrical decrease in our rate of motion through time.

10. Jul 29, 2004

### Sugien

if it is only motion that causes the perceived time dilation effect why would you need to travel into space? Could you not vibrate an object at a frequency equal to the velocity required for time dilation? In other words in the twin paradox instead of one long journey out to a distant star and back would not 10K small journeys out and back to a point 1/10th the distance away be the same as one long journey? if that is so then a vibration is the smallest of all journeys. Could you not cause an object to vibrate and a significant percentage of light? Of course for this primus it would have to be a given that the object could withstand such a sever shaking.

11. Jul 29, 2004

Staff Emeritus
You would have to vibrate the object so the average velocity is some large fraction of c. That suggests the object should be small, and lo and behold, we have such small vibrating objects in the atoms and molecules of crystals. I don't know if this experiment has been done.

But the twin phenomenon has famously been confirmed by experiment. Muons are created 60 km up in the atmosphere by cosmic rays striking atome of oxygen at very high energies. It takes these muons at least 200 ms to reach the ground (60 km over c, a lower limit). Now the half life of a muon in its own rest frame is measured to be 1.5 microseconds, so the expected fraction that reach the ground would be (1/2)133 ~ 10-40. (you get the 133 by dividing the half life into the elapsed time). But in fact we see 1/6 of the muons! The answer of course is that the muons are travelling at a high fraction of c relative to the ground, and their time is dilated just like the traveling twin. So the arithmetic has to be done with the dilated half life time, not the muons rest frame time. (example and numbers from Spacetime Physics by Taylor and Wheeler).

12. Jul 29, 2004

### Njorl

"How long till we can travel into the future? "

Once you get there it becomes the present. This makes time travelling with the kids really irritating.

"Are we there yet?"
"NO!"
"Are we there yet?"
"NO!"
"Are we there yet?"
"NO!"
"When are we going to get to the future?"
"In one instant."
"Are we there yet?"
"NO!"
"Are we there yet?"
"NO!"
"Are we there yet?"
"NO!"

Njorl

13. Jul 29, 2004

### Enginator

Hi, I'm new here. You just blew everything I THOUGHT I new about relativity out of the water. :surprise: But then, it has been a while since I've studied anything on it. Looks like I have some catch-up to do. Where can I read more about the concept that "we are always moving through space-time at the speed of light?" I don't feel like I'm moving that fast. I mean, I'm only 190 lbs....heh....

14. Jul 29, 2004

### Vast

Not sure I understand why less hit the ground though.

15. Jul 29, 2004

### Vast

Sorry for the childish irritation, it’s only because I hate living in the 21st century.

And of course it’s always the present for you…

16. Jul 29, 2004

### Prometheus

Try an introductory book on relativity or space-time.

Look at anything around you. Look at the buildings outside your window. Do you feel like they are in motion at all? I suspect that you do not feel like they are in motion. Yet, the earth is in motion around the sun, the solar system is in motion through the galaxy, and the galaxy is in motion through the universe. I submit that your feelings are irrelevant when it comes to understanding rates of motion in space-time.

Look at some person walking or running. How fast is he moving? How are you even aware that he is moving? You see him. What does it mean to see him? It means that you see light that is emitted by him. How fast is his motion? He can only be moving as fast or as slow as the speed of the light. THere is only one speed in the universe, the speed of light.

The motion of light has both spatial and temporal components. The speed of light is constant in space-time. The speed of light is not constant in space or in time, but only in space-time. The speed of all objects in space-time is equal to and is dependent upon the speed of light. All of your awareness of objects in motion is through awareness of their light. All motion in space-time is subject to the motion of light. Light enables the interaction of space and time to create space-time.

17. Jul 29, 2004

### Enginator

Prometheus: I have read an introductory book on relativity (Eintstein's) and Michio Kaku's Hyperspace (which is the most recent thing I've read and is admittedly a bit old now). I simply don't remember anything in there saying we are all traveling at the speed of light. My comment about not "feeling" like moving that fast had more to do with my weight than the feeling. I mean, doesn't the mass of the traveling object go to infinity at the speed of light? I don't feel infinitely heavy....close, though. I just had three pieces of cake for someone's office birthday...(yuk).

Now, when you say I see someone walking, I see the light "emitted" (actually reflected) by him, are you saying that because the only thing that I am seeing/sensing is light, then that is how fast he's moving? If so, then we are not actually talking about the movement of his mass that is at the speed of light but the light reflected off of him, right?

18. Jul 29, 2004

Staff Emeritus
In four dimensional spacetime your momentum is a vector which is the sum of two othe vectors: one of them is your three dimensional momentum and the other pints in the time direction and has length equal to your energy (in appropriate units). In your rest from, the spatial momentum is zero, but the time directed one remains, its magnitude is now your rest energy, given by mc^2, and multiplied by the speed of light. In fact that time component always has that factor of c in order to give it the same units as the space components.

The magnitude of your four momentum is a Lorentz scalar, the same in all frames. In the rest frame this is all due to the time component, but in other frames it's a sum of contributuions from time and space components. So it can be looked at that you always have a time component of momentum, which is its max when looked at from your rest frame.

This is the source of the idea that we are all moving in time at the speed of light. I believe Greene alludes to this idea in Elegant Universe.

19. Jul 29, 2004

### Enginator

Ok, I found this (http://www.raindrop.com/text/perspective_timedist.html) which seems to explain it a little more clearly to me. Here's what I still don't understand how to reconcile.

1. How does mass fit into the vector?

2. If photons have a "0" time component in the vector, why do we see lights "go out?" Because for us, their relative time component is infinite, right?

:uhh:

20. Jul 29, 2004

### Prometheus

This is a confusion of the context of the "speed of light". In a Newtonian sense, the speed of light is a measure of motion through space, irrespective of time. In the Newtonian context, the speed of light refers to the maximum rate of motion through space that is possible, the rate of motion through space of light. When people make this statement about mass, they are refering to motion through space at the speed of light, devoid of the time component. As an example of the prevalence of this confusion, consider subatomic particles. Subatomic particles are considered to move at the speed of light. Why, then, does the mass of each of them not go to infinity? The reason is that in relativity there is a time component, and thus that nothing but light can ever move at the Newtonian speed of light.

Do not think that the speed of light is constant, or that the speed of light is constant in space. It is not. The speed of light is constant in space-time. Everything always moves at the speed of light. I am not saying that everything always moves at the Newtonian speed of light, which is the maximum rate of motion through space. There is always a time component, such that the space component can never be 100% of the motion, what people often refer to as the speed of light, but which is only the Newtonian speed of light, wherein time is not a factor.

Emitted, not reflected. When light hits the object of your vision, the object absorbs that light and responds by emitting light. You then observe the emitted light.

No. Light enables the binding of space and time into space-time. Not only is light the enabler of space-time, but it is our only source of awareness of space-time and of motion through space-time. My point is that light is our only source of awareness of motion through space-time because light is the enabler of that motion.