# Do we have momentum in traveling in time?

1. May 8, 2015

### 1832vin

this may sound extra ridiculous
there's stuff like time evolution for wave functions, and alot to do with time
but i've thought, isn't time also a dimention? ( i know it's not a spacial dimention, but does it mean it has completely different properties?)
since we are traveling in time at a constant rate (we presume), as like traveling through spacial dimentions, does it mean there's energy to it? and as you travel close to the speed of light, you experience time less (due to time dialation and others)
then does it mean the higher energy(in spacial dimention) = less energy in time dimention?
traveling at a speed means have energy to accelerate and decelerate other objects
why would we return back to normal time progression after time dialation>? where did we got that energy(time energy?) back?

and where did the energy came from to make us move foward in time?

2. May 8, 2015

### arivero

Momentun in time direction is exactly the definition of Energy.

3. May 10, 2015

### Blackforest

In my eyes, fundamental questions are never ridiculous. Thanks for questioning and questioning again. We usually don't take the time to ask how all this (our world) works.

4. May 10, 2015

### Right

Strictly speaking, I'd have to venture a no. Light has no weight, and thus no momentum. Time, as far as we know, doesn't have matter. It isn't composed of matter.

In a more abstract sense though, its possible. However, much of this question is relative since we don't have any obvious way to create controlled and testable conditions. Perhaps the passage of time, unbeknownst to us, has been slowing or speeding up since the big bang!

We do know that gravity has some subtle but well known effects on time. Imagine a satellite in a highly elliptical orbit. As it reaches its periapsis (lowest point of orbit), it will be moving away from its parent body for half its journey, and thus experiencing less gravity. If time did have momentum, then with each orbit, time would stretch and compress, spending some form of energy. Without positing some unsupported extra-dimensional banking of time-energy, this behavior should stop as the energy source depletes. I speculate that this doesn't happen.

Okay I'm getting a bit lost with this thought experiment, take it for whats it is - half baked.

5. May 10, 2015

### 1832vin

interesting thought experiment, and i'm going to try expanding on it

but the problem is, that we cannot measure relative time, (well we can, but not in a way that we can compare it)
we might want to make an oscillator that oscillates close to the speed of light, or a spinning device
then we might be able to get some relative time comparisons

6. May 10, 2015

### sophiecentaur

I assume you mean Mass, here. Light (photons) certainly do have momentum, despite being massless. The momentum of a photon is h/λ so you can see, as it is inversely proportional to wavelength, the momentum gets higher as the frequency (c/λ) increases. Direct evidence of this is Light Pressure (look it up).
The definition you are using for momentum only refers to the momentum of objects that have mass. That works fine for most purposes, involving mechanical problems.

7. May 10, 2015

### Staff: Mentor

This thread is starting to drift into speculation here.

It is indeed possible and even natural to treat time as a dimension. When we do, we can still describe motion using vectors, except that instead of having three components (x, y, and z) the momentum "four-vector" has four components (x, y, z, and t). This four-vector approach is an important part of the modern formulation of special relativity and is essential to move on into general relativity. And as arivero hinted in post #2 above, when you write the momentum as a four-vector, its time component becomes the energy of the object.

We're leaving this thread open for now, but it would be a good thing if all participants would first google for "momentum four-vector", ask questions about what they don't understand, but not offer speculations that ignore what physicists have already learned over the past century.

8. May 10, 2015

### Right

Yes, I meant mass. And I stand corrected! Silly me with my Newtonian thinking.

I can take a hint Nugatory.