# Negative time

1. Aug 10, 2011

### Vinni

Hello All I'm new to the forum and have a question.

I was looking at the time dilation function and noticed that negative time would be described with imaginary numbers and be a kind of anti-time, albeit that rest mass can not be pushed faster than the speed of light but for the sake of brevity say FTL is possible. That being the case then negative time would result as a change in the direction of momentum and not in the proverbial backward time travel of H.G. Wells' "Time Machine". With negative time atoms would fly apart, electrons would cling to electrons, protons would cling to protons, matter's usual behavior would be vastly different.

Am I wrong with this conclusion? Also would gravity be affected, since there is no such thing as anti-gravity, could anti-time(negative time) create anti-gravity?

2. Aug 10, 2011

### edgepflow

Special relativity does not let you push any object initially less than the speed of light to a speed that equals or exceeds the speed of light.

But special relativity (as far as I know) does not prohibit an object originating at FTL. But an object that starts FTL, can never slow down to light speed or less. These hypotherical particles are called Tachyons.

3. Aug 10, 2011

### Vinni

Considering that there is no causal mechanism that warps space because of the presence of matter physicists would conclude that negative time has no effect on gravity!

Would this be an accurate interpretation of general relativity?

4. Aug 10, 2011

### WannabeNewton

When you say negative time are you talking about a time translation in the negative t direction?

5. Aug 10, 2011

### edgepflow

I don't know about negative time, but and interesting thing happens if you develop an equation for relativistic energy for a Tachyon: the mass must be imaginary since the ratio of two imaginary numbers is a real number. For example, i = sqrt (-1), then i / i = 1.

So the question is does imaginary mass affect space time according to general relativty?

6. Aug 11, 2011

### Staff: Mentor

What do you mean by this?

In the equation:
$$\Delta t' = \frac{\Delta t}{\sqrt{1-v^2/c^2}}$$

A negative $\Delta t'$ would imply a negative $\Delta t$, but I don't see where any imaginary numbers would come in.

7. Aug 11, 2011

### nitsuj

8. Aug 11, 2011

### Passionflower

Proper time, is an interval between two events, this in GR, can never be negative, i.e. clocks never go backwards.

9. Aug 11, 2011

### Vinni

You're right! Even if I used imaginary numbers to represent the roots of $$1-v^2/c^2$$ when v is greater than c

$\Delta t' > 0$

Since $$i = \sqrt{-1}$$

So this means v > c or v< c and v != c if hypothecally v is allowed to be FTL and the absolute value of the denominator is used. Then does it make sense that a particle can quantum mechanically tunnel beyond c by transforming into a tachyon, hypothetically?

10. Aug 11, 2011

### Ossama

I read that there is two kinds of time :

past time which has the value of -it

future time which has the value of +it

and by the multiplication of them we obtain the square of our present time which we live in !

Time is deeply connected to the concept of Entropy which is "time arrow" , and if we want to discuss the direction of the time we will be forced to speak about entropy and thermodynamic processes , I think so.