A time machine sounds great. We’d all love to go and change something wouldn’t we? Or would we?

A time machine for an observational tool may be of use, but for any other purpose they would be bad, very bad. First - there is the silly hypothesis - if someone was going to invent a time machine, why haven’t we seen one already, why have they not come back to our time?

This leads to some interesting thinking. First - if you were from a future, and you could hand your past self technology from the future, you would have to consider that nothing in your life since that point was worth anything, as it would potentially alter everything.Would you really do that? Would really wish to undo everything, not just the bad stuff but all the good stuff?

Who could wish away children, partners, friends and other things? It just sounds like you’d have to be movie stereotype traumatised bad guy to want to change anything, or so naive about causality that you’d not be let near a time machine to do so.

So very few from the future would both have capability or want to use it in that way.

What about observing the past?

This may be a use, but you would end up needing to take such care to avoid interfering with the future - so much so that having any kind of physical presence - the elimination of bacterial colonies or change in balances of chemistry may have massive effects.

Consider a line on some paper that leaves from one point, and coincides with another collinear point. Alter it by a fraction of a degree and it will no longer do so. Make that extrapolation much larger and the most minor deviation is no longer converging. Even the smallest change may have massive side effects. Even sending a remote controlled camera drone could alter the course of history beyond all recognition.

So this may not be a good idea.

What about going to the future?

If you were able to take a time machine to a future, a future post time-machine, then a future society may take great pains to ensure that you take nothing - no technology or forward knowledge back with you - because the last thing they would want is for you to create a different future where theirs never existed.

Are there alternatives to these?

Yes - it is also possible that history is what it is, and going around time travel is part of the deterministic path it has/will/is following already. In which a time machine achieves nothing and is useless too. This is dangerously close to the concept of their being no free will and us merely being gears in a great machine.

I am probably wrong about this - but as much as I love Doctor Who, perhaps the bigger on the inside thing is far more useful than time travel.