# Will we go the the past if we could go faster than speed of light?

1. Feb 11, 2010

### altairz

On a forum I read that we don't know what would happen if we went faster than speed of light. On a video, I heard that we would go to the past if we went faster than c.

Im confused, what is right?

2. Feb 11, 2010

### tiny-tim

Hi altairz!

It's all rubbish!

We can't go faster than light, and according to the equation t' = t√(1 - v2/c2), if we could, our age wouldn't be multiplied by a negative factor, it would be multiplied by an imaginary factor!

3. Feb 11, 2010

### altairz

thanks for answer :).. But what do you realy mean with imaginary factor :p? ( sorry, I'm new to physics :P )

4. Feb 11, 2010

### tiny-tim

I mean that the time-dilation factor √(1 - v2/c2) becomes the square-root of a negative number, and is therefore imaginary.

5. Feb 14, 2010

### NYSportsguy

"Time" is described as going from a state of less entropy to more entropy. Or from hot to cold in energy-temperature terms.

I am not really sure what velocity (light speed) has to do with that.

6. Feb 14, 2010

### higgsnerd137

For something with mass to travel at c, it would have to have infinite density. That is why the photon is massless.

7. Feb 15, 2010

### map19

Draw a diagram of time vs distance. Normally this is done with axes of years (vertical, time, both pos and neg.) and lightyears (horizontal, distance).
At a speed of c the graph is at 45deg. One lightyear travelled in one year. when extended in both horizontal directions this is called a light cone. It indicates the area inside which physical processes from the source can be experienced. Outside the cone is forbidden by Special relativity.
At 2c the graph is at 26deg, but still positive time.

To get to horizontal you need infinite speed. You can never go negative.

8. Feb 16, 2010

### Frame Dragger

Travel in time is a function of a spacetime geometries that allow for such travel, not velocity. For speed to be a factor, you would need to be one of a two cosmic string whipping past each other, and even then the result wouldn't be as desired.

9. Feb 27, 2010

### v2kkim

I can imagine that you move faster than speed of light, like you are at point A and after 1 sec point B (2*c distance) .. etc. which is a purely imagination. Then you will see the earth event moving backward, on which I am sure.

10. Feb 27, 2010

### melkorthefoul

IF and this is a rather big IF, you cold travel faster than light, people say you will go back in time because-
Lets take a scenario. The year is 2010, yes? Lets say there is an outpost 42 light years away from Earth. If i get on a ship that can travel 42c, I will reach that outpost in 2011, yes? But, if (here we go again) I take a huge telescope and take a peek at the moon, I will see the light that reflected off the Apollo Mission in 1969... so have I travelled back in time?

No, because the year is still 2011. However, I can see past events, as I have overtaken the 'messenger' who 'delivered' the 'message'