Physics often makes a fool of our gut feelings. James Gleick, author of Time Travel: A History makes this point using the most elemental example. You, sitting or standing to read this now, your gut feeling and experience tells you that you’re sitting or standing on a flat plane, on an immobile surface. Science has some news for you though, in Gleick’s words: “You’re actually on the surface of a giant sphere that’s spinning at high speed and hurtling through space, and by the way there’s no difference between up and down except an illusion that’s created by the force of gravity.”

Radical readjustments of accepted perception is central to the nature of physics – even if something isn’t proven, our mind has to stay open to the possibility that maybe, things aren’t as we see, feel or intuit them to be. This is particularly relevant to the debate surrounding time. Does time exist, or doesn’t it? Is time only inside our minds, or is it a force acting upon us? It might seem ridiculous to question the existence of something that radically shapes our lives – our days, hours, minutes, our life span, our grandparents, our grandchildren.

Einstein’s teacher and contemporary Hermann Minkowski offered his vision of space-time as a single thing, a four-dimensional block in which the past and the future are just like spatial dimensions, with a north and a south. Some physicists say there is no distinction between the past and the future, and that time is a dimension just like space.

This seems at odds with what we feel, which is that the past has happened and the future is not yet determined. The future and the past are different to us, but in physics they’re the same. Gleick’s realization in the face of the multiple hypotheses on time is that just as our feeling about the stability of the surface we walk on is not so simple, our perception of time may also be radically more complex than we think. At this point, every expert’s ideas in this debate are provisional, but we have an obligation to take these ideas seriously.

James Gleick’s most recent book is Time Travel: A History.

James Gleick:  There is a sort of funny things that you hear people say that time doesn't actually exist. And it's something that physicists argue about, I mean physicists actually have symposia on the subject of is there such a thing as time, and it's also something that has a tradition in philosophy going a back about a century. But I think it's fair to say that in one since it's a ridiculous idea. How can you say time doesn't exist when we have such a profound experience of it, first of all? And second of all, we're talking about it constantly. I mean we couldn't get – I can't get through this sentence without referring to time. I was going to say we couldn't get through the day without discussing time. So obviously when a physicist questions the existence of time they are trying to say something's specialized, something technical. Einstein offers, Einstein or maybe I should say more properly Minkowski, his teacher and contemporary, offers a vision of space time as a single thing, as a four dimensional block in which the past and the future are just like spatial dimensions, they're just like north and south in the equations of physics.

And so you can construct a view of the world in which the future is already there and you can say, and physicists do say something very much like this that in the fundamental laws of physics there is no distinction between the past and the future. And so if you are playing that game you're essentially saying time as an independent thing doesn't exist. Time is just another dimension like space. Again, that is in obvious conflict with our intuitions about the world. We go through the day acting as though the past is over and the future has not yet happened and might happen this way or it might happen that way. We could flip a coin and see.

We tend to believe in our gut that the future is not fully determined and therefore is different from the past. But physicists will say, and it's certainly true that a lot of things that we feel in our gut turn out not to be right. We feel in our gut that we're sitting on a flat plane on a surface of something that's immobile. And if a scientist came along and told you that no you're actually on the surface of a giant spear that's spinning at high speed and hurtling through space, and by the way there's no difference between up and down except any illusion that's created by the force of gravity, well you'd have to do some radical readjustment of your understanding of the universe to accept that your first intuitions weren't correct. And so if a physicist comes to me and says do some readjustment. Face it, the future looks different from the past to you but actually physics tells us it's the same, I at least acknowledge that I have an obligation to take that seriously to listen to it. And physicists do argue about these things and it's fair to argue about it. And it's an argument that I take a position on in my time travel book because I felt I had to or maybe I had a position and yet it's got to be a qualified position. And that's what I recommend to readers of science fiction and to physicists to remember that your views of these things are provisional.