Seymour asked:

We all know, currently, it’s impossible to ‘scientifically’ or ‘physically’ go back in time. But if you had the dying urge to do so, say if you wanted to correct a critical mistake you made, and provided you would not disastrously change the cause of history by doing so, could the following be plausible: you are given a drug which puts you in a coma for the rest of your life. You have a dream in that coma that lasts from when you were knocked out until your real-life death. The events in the dream start the day before you do this bad thing, so you can do something different instead. So essentially, this drug simulates your life from a certain point until your death.

My question is, is this the same as going back in time in reality (‘scientific’ or ‘physical’ time travel)? Or even, is there a difference between the two? And, what’s more important, the ‘reality’ of life, or our interpretation of it, or are they the same (because everyone has different interpretations)?

Answer by Helier Robinson

It depends on what you mean by ‘the same’. If you mean similar then of course the dream and reality are similar, except for your not doing the bad thing. If you mean identical, or one and the same, then of course the dream is not reality: dreams never are. Similarity has a plurality of terms, identity has only one; and ‘the same’ is ambiguous about these. Secondly, what do you mean about the reality of life? Reality is usually defined as all that exists independently of what anyone believes about it, and beliefs about it are true if they are similar to it, and otherwise false. So reality and a belief (or interpretation) about it are two, cannot be one; so what do you mean about them being ‘the same’?


Answer by Geoffrey Klempner

Before I answer your question, a spoiler alert. Don’t read this if you haven’t seen (but are planning to see) the movie Vanilla Sky (2001) starring Tom Cruise and Penelope Cruz, a remake of the movie Open Your Eyes (Abre Los Ojos, 1997).

What you describe is basically the plot of Vanilla Sky. Honestly, I would much rather you saw the movie than read my answer (read the answer afterwards!).

OK, so we learn late in Vanilla Sky (warning, this is the big ‘reveal’) that much of what we thought was taking place in the life of the main character played by Tom Cruise, is actually a lucid dream. Following a disfiguring accident, he chose to be put to sleep, dreaming of the life he would have lived had the accident not taken place (he gets the girl, lives happily ever after, etc.). (This is a near-future where ‘dream machines’ have been developed.)

Unfortunately, things don’t go as planned, and the dream morphs into a nightmare, forcing Tom into the big decision to have himself woken up to face the consequences of his actions in his ‘real’ life.

And that’s the point. Regardless of how well the dream machine works, you can always be woken up. That’s one definition of ‘reality’. An experience isn’t ‘real’ if there is the possibility of one’s being woken up.

That opens a can of worms, however. What kind of ‘possibility’ is this? I can conceive of the possibility of ‘waking up’ after I have finished writing this answer, to find that I am a nine-footed purple monster on the planet Zog who dreamed of being ‘human’. Is everything we can coherently conceive (in what sense of ‘conceive’?) actually possible?

I once thought I had an answer to this question, but I am not so sure now. ‘Reality’ is just whatever we take reality to be now, and if we find we were wrong (we wake up) then we just revise our definition.