Can we go back in time?
image source: http://epod.usra.edu/blog/2009/04/frost-flower.html
I know many people have tried to answer this classic question, but I’d like to answer it again, with my own words.
As for “going across the time”, I think it’s quite possible, “theoretically”, though not easy, practically.
To try to grasp this concept, I’m afraid first we have to come back to the basic concept of TIME.
What is TIME?
At the first sight, TIME seems to be intuitive, but actually it’s quite volatile and something not so easy to picture.
We know when things change, time emerges. So now we can safely say: TIME is some kind of change in the space.
If we think of the space as a collection of points, we may raise such a question: Do the points change the same way? If not, what would the time be like?
Many smart people have been working on this problem for centuries.
My own answer is: On large scale, the points in the space my change the almost the same way, and we can have almost same physical laws to describe the way they change. But on small scale, there could be tiny differences on how they change. What does this mean? It means on small scale, TIME differs for different points in the space.
It also means, on small scale, these tiny points follow different laws in the space. Some physical symmetries are correspondingly changed.
So a conclusion could be drawn: If we want to change time in a space, we also have to change the dynamic physical laws the space follow. In such a way we make that space different than the other space left in the universe.
Now you might have figured out how to go back in the time, right?
By now we usually assume that time in the Universe are even if we don’t consider the effect of physical fields. But is this assumption unquestionable? I’m not so sure …
If one day you happen to notice that the world around you evolve in different speed or couldn't be put on the same page, then congratulations, you might have discovered a new physical law in your own space and TIME!