# Does antimatter go back in time?

1. Mar 17, 2012

### lmoh

Is it true that antimatter is positive matter traveling backwards in time? I have recently heard some say that it is and is part of the mainstream interpretation, but others say that it shouldn't be taken too literally, but I myself am not sure. What is the general consensus on the matter if there is any?

2. Mar 17, 2012

Staff Emeritus
It has been known since at least 1964 that this cannot be the correct description of nature.

3. Mar 17, 2012

### Khashishi

Vanadium, could you say a little more about what happened in 1964?

4. Mar 17, 2012

### A.T.

First of all, you have to define what "going back in time" means. In Relativity there are two concepts of time:
- coordinate time is measured by a clock at rest in frame of the observer
- proper time of an object is measured by a clock co-moving with the object

AFAIK the "antimatter going back in time" idea refers to proper time. I'm not sure how useful the idea is, but here some points:

In Feynman Diagrams the anti particles are shown to be moving back in time:
http://en.wikipedia.org/wiki/Feynman_diagram#Electron-positron_annihilation_example

There are also the Epstein diagrams which contrary to Minkowski diagrams don't use coordinate time, but rather proper time on the time axis. In this diagrams the length contraction from movement can be derived from the projection of the object roated in space-time onto the spacial dimensions:

Raum = space
Eigenzeit = proper time

Object at rest in space moving only through time, therefore advancing vertically in space-time (only along the proper time dimension):

Object is now also moving in space, therefore advancing obliquely in space-time, therefore rotated in space-time, therefore contracted spatially:

Now, what would happen if the proper-time component of that space-time-advancement vector would become negative, so the arrow points down?

Obviously the spacial projection would not only be contracted but mirrored. And anti-matter shows properties which are mirrored compared to matter. So it might make sense to interpret matter and anti-matter as advancing in opposite directions along a proper-time dimension.

Note that "forward" & "backward in time" become arbitrary. An alien made of anti-matter would claim that we are moving backwards in proper-time.

Last edited: Mar 17, 2012
5. Mar 17, 2012

### alexg

Well, we've created antimatter, and held it in suspension for as long as 16 minutes. It showed no tendency to move backward in time. Otherwise, it would have vanished as soon as it was created.

6. Mar 17, 2012

Staff Emeritus
No, no, no. That's not what the arrows mean. The arrows are mnemonics, nothing more, nothing less. They tell you whether you need a u, a v, a ubar or a vbar (depending on incoming or outgoing).

7. Mar 17, 2012

### lmoh

I'm sorry, but I cannot help you there, due to my lack of knowledge on the subject, but I am only repeating claims by other people, but Feynman's interpretation is relevant if that helps.

8. Mar 17, 2012

Staff Emeritus
The discovery of CP-violation by Jim Christenson et al. That demonstrated that the laws of nature were not time-symmetric. That is enough to tell you that "moving backwards in time" is not a well-defined statement. And since it's not a well-defined statement, suggesting that particles do it is not meaningful.