Time: Do the past, present, and future exist all at once? | Big Think

MICHELLE THALLER: Is time real or is it an illusion? Well, time is certainly real, but the question is what do we mean by the word time? And it may surprise you that physicists don't have a simple answer for that.

JAMES GLEICK: Physicists argue about and 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 back about a century. But, I think it's fair to say that in one sense 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 specialized, something technical.

BILL NYE: Notice that in English we don't have any other word for time except time. It's unique. It's this wild fourth dimension in nature. This is one dimension, this is one dimension, this is one dimension and time is the fourth dimension. And we call it the fourth dimension not just in theoretical physics but in engineering. I worked on four-dimensional autopilots, so you tell where you want to go and what altitude it is above sea level and then when you want to get there. Like you can't get there at any time.

GLEICK: 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're 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 it 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.

DEAN BUONOMANO: If the flow of time, if our subjective sense of the flow of time is an illusion, we have this clash between physics and neuroscience because the dominant theory in physics is that we live in the block universe. And I should be clear. There's no consensus. There's no 100 percent agreement. But the standard view in physics is that, and this comes in large part from relativity, that we live in an eternalist universe, in a block universe in which the past, present and future is equally real. So, this raises the question of whether we can trust our brain to tell us that time is flowing.

NYE: In my opinion, time is both subjective and objective. What we do in science and engineering and in life, astronomy, is measure time as carefully as we can because it's so important to our everyday world. You go to plant crops; you want to know when to plant them. You want to know when to harvest them. If you want to have a global positioning system that enables you to determine which side of the street you're on, from your phone you need to take into account both the traditional passage of time that you might be familiar with watching a clock here on the Earth's surface, and the passage of time as it's affected by the speed of the spacecraft, and the passage of time as it's affected by the gravity of the Earth itself, both special and general relativities. It's astonishing. We work very hard to measure time with all sorts of extraordinary clocks, but there is no question that with our brains, which are wet chemical computers, we lose track of time. We don't know i...