# Negative time

1. Oct 21, 2005

### Nabbsy88

Does anyone know whether or not negative time exists. in any way shape or form.

I have seen several papers on negative time and have read it does exist in the boundries of parallel universes.
I was wondering if anyone had any info at all on this subject.

2. Oct 21, 2005

### ComputerGeek

you mean it exists between separate 'branes?

3. Oct 21, 2005

### Norman

No the arrow of time is well defined. Time flows in one direction. Why it does is a different question. And unsolved. But for certain elementary processes there is a symmetry called "time reversal" in which the $$T: t \rightarrow -t$$. This is not an exact symmetry and is not obeyed by the decay of the Kaon (K meson) or the 2nd law of Thermodynamics.

Negative time and the boundries of parallel universes is outside my area of expertise and I cannot comment. But, negative time has not been observed (could it?).

4. Oct 21, 2005

### vanesch

Staff Emeritus
The problem with questions like these is that you ask about a term, taken totally out of context, without (probably) having an idea what could be meant by it, in what theoretical frame.
In a trivial way, I could say that the concept of negative time surely exists: if you go forward in time -24 hours, you arrive at yesterday. In the same way as when you go -5m to the right, you actually went to the left.
Negative time as a difference between two moments just tells you something about the order.
But it is my suspicion that you want to talk about something else than that... Now, before I bring up anti-particles, tell me what it could possibly mean to you, "negative time".
cheers,
Patrick

5. Oct 21, 2005

### MooMansun

What exactly do you mean by going 'forward' in time?

Is time just a representation of the observation of motion?

A better way of putting this is, we know that time is relative is to the speed of the observer. If this is the case, then what we describe as the time arrow could simply be the flow of that motion, that is, it moves in one direction, rather like a river flowing to sea.

Under this concept, the slowing of time, would actually be an expansion of distance of space, a warping effect.

Whilst this may sound philosophical, I assure you it is not. Also, it is not a theory I am presenting, but rather a demonstration that this process can be described differently.

I think it is an important distinction.

Is anyone aware of a physical aspect associated with time?

6. Oct 21, 2005

### derz

If you mean time as a 4th dimension then yes, I think everyone here is aware of that.

7. Oct 21, 2005

### pervect

Staff Emeritus
Space-time is 4-dimensional, but the geometry of space-time is not Euclidean. When Tetraspace is talking about the geometry of 4 dimensions, they are talking about a 4-dimensional Euclidean geometry. This is not the same as the 4-dimensional geometry of relativity, though both are examples of 4-dimensional geometries.

The geometry of space-time is not the geometry of distance (as is conventional geometry), but the geometry of the Lorentz interval. The Lorentz interval is used instead of distance because the Lorentz interval is the sole invaraint of the Lorentz transformations. This means that the Lorentz interval it is the only quantity that all observers agree is "the same", regardless of how fast they are moving. Distance is not the same for all observers, as is illustrated by length contraction. Time is also not the same for all observers, as is illustrated by time dilation. But the Lorentz interval *is* the same for everyone.

8. Oct 21, 2005

### Nabbsy88

Thanks

Thanks guys for your help i have found recently that 'negative time' does infact exist in the boundries of parallel universi,but however has not been proved or disproved in our physical universe.

9. Oct 21, 2005

### masudr

That is technically not true; any scalar (in the Lorentz space sense) such as $p^\mu p_\mu=\frac{E^2}{c^2}-p^i p_i$ or $F^{\mu\nu}F_{\mu\nu}$ as well as $x^\mu x_\mu$ (and so on) are invariant under Lorentz transformations.

10. Oct 21, 2005

### MalleusScientiarum

Negative time also arises in the context of many-body fermi systems, and corresponds to a "hole" in the particle-hole picture propagating forward in time.

11. Oct 22, 2005

### vanesch

Staff Emeritus
Yup that's what I was alluding to in the beginning of this thread

12. Oct 22, 2005

### pervect

Staff Emeritus
The point I was trying to make was about how space-time coordinates transformed - thus I was only considering space and time, and quantities directly derived from them.

13. Oct 22, 2005

### RandallB

If you’re looking for just a small foot hold to legitimately argue for time going backwards or “Negative” to score points with your teacher. You’re right you won’t get far using parallel universes or 'branes’ (as in a membrane for our cosmos, more mean other universes)? Those are all great for the ideas, but no one claims any real proof that “other worlds” are real.
However treating this more as a homework problem – I’m not sure what “A Level” Physics means for – is that the 12th grade as in Senior year High school State side?
But if your actually discussing things like this in class you should have heard of Fynman and his lectures. Look back at some of that to find evidence within or our world if we restrict our view to the few feet around a particle collision being observed in a lab. (Bubble chambers etc.) He gave good arguments that the only way to explain some of the reactions observed is that some electrons were actually positrons moving backwards in time, or some positrons were actually electrons moving backwards in time. Of course all concluding reactions ended in things moving forward in time. See “Fynman diagrams”.
It’s the only ‘toe hold’ I’d suggest an an “any way shape or form” angle to argue negative time is real. Even it’s just a couple nano-seconds in duration; if it’s real it’s real “in our physical universe”.
Have fun with Fynman Diagrams.