The simplest answer is that time travel cannot be possible because if it was, we would already be doing it.

 The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of thermodynamics or relativity. There are also technical challenges: it might be possible but would involve vast amounts of energy.

end Partial quote from:

https://www.sudbury.com/beyond-local/beyond-local-is-time-travel-possible-5489600

My theory would be that time travel is older than the planet Earth. How much older I have no idea.

Time travel is happening but since time travel is 1000s or even millions of times more dangerous than Hydrogen bombs I can see why it is kept a secret on pain of death worldwide now.

Also, every time you change time many things change not just one. So, there is ALWAYS collateral damage when you change time.

For example, each time a city on earth was blown up with nuclear weapons since the end of World War II it has been retroactively been returned to normal before the blast since the end of World War II.

You might ask why were Hiroshima and Nagasaki left blown up?

I think this decision was simply as a warning to mankind not to repeat this mistake. Some learned from these mistakes and others didn't.

So, correcting time after nukes happen that blow up cities, military bases, whole countries or the earth itself has happened over 50 times or more at this point.

This is why we still have a planet that is not an asteroid belt today (like the planet out past Mars that IS an asteroid belt for the last 65 million years that some of our ancestors blew up.

Note: The point is time travel HAS TO remain secret because of the thousands to millions who would naturally disappear out of time every time a nuclear event is corrected in time retroactively.

However, the point seems to be always: "IT is better that some humans survive here on earth rather than no humans survive here on earth. Also, it is better that earth and whatever ecology can survive should survive rather than earth becoming a permanent asteroid belt with everything living,  dead permanently."