Is time REALLY an illusion?

Einstein said “…for us physicists believe the separation between past, present, and future is only an illusion, although a convincing one.”

And from another site: “Roughly speaking, the problem is that in the equations of modern quantum-relativity physics there is no time. You have changing states of being, but no state is intrinsically “later” or “earlier” than any other. Time is just the fourth dimension of space, and in theory it is possible to return to any earlier period of spatialized “time”, in the same way that it is possible, on a plain, to move from point a to point b and back.”
Was Einstein essentially saying that time is an illusion? An illusion means that one is being convinced that something that doesn’t exists actually does. Certainly time exists, no?

I’ve never seen that particular quote before, nor any commentary on it by anyone who knew Einstein. But I think what he’s trying to say there is that the mystery of time is an illusion. That is to say, we understand time just as well, and in the same ways, as we understand space. If time seems mysterious (or rather, more mysterious than space), that’s just an illusion, since mathematically, physicists treat time and space in the same manner.

Certainly time exists. Some physicists claim that the *flow *of time from past to future is an illusion, but that’s not quite the same thing.

The problem with saying that time “flows” or “passes” is, if time passes, how fast does it pass? One minute per minute? One day per day? You can see that’s meaningless. Likewise, what exactly *is *the distinction between past, present and future? *Every *point in time is a “present” moment, when it happens. You can’t make sense of these concepts without assuming that time “flows”, but that brings us back to the problem mentioned above.

Personally I go along with (I think it was) St Augustine, who said something like “I know perfectly well what time is, as long as no-one asks me to explain it”.

Here is an episode of my favorite radio show which gives a fascinating and incredibly accesible illustration of the subjective quality of time perception. The whole episode is great, but the relevant segment starts at about 24 min. (note: Brian Greene is the guest).

This quote would apply equally well to pornography. :eek: :smiley:

I would just add… “the separation between past, present, and future” could mean a thousand years past, the present, and a thousand years in the future. Or it could mean one second in the past, the present, and one second in the future. Both could be significant. An analogy for baseball fans… consider Bill Buckner’s career. Before that fateful night… he was quite a solid player. Not Hall of Fame by any means, but a player. But after that one instant where he booted the ground ball, the whole perception of “Bill frickin’ Buckner” changed. Same with “Bucky frickin’ Dent”.

It’s all relative. :stuck_out_tongue: As Einstein said. The change from those two examples above, from one second to the next, are pretty much the same from 1065 to 1066. Or 1066 to the present.

The human animal has evolved to perceive visible radiation in a way useful for its navigation and survival - and the visual model of the world could be said to be illusory, as it is constantly constructed and updated by the mind.

In a similar way, is human perception of time shaped by evolutionary usefulness? Presumably we need to perceive change in the external world (which I suppose time is just a measure of, really) quickly enough to avoid predators, but as we don’t need to catch flies out of the air, we have less need for millisecond reactions. Would these sort of factors influence the perceived speed at which time passes? Or does it entirely depend on whether we’re having fun?

I don’t know.

The reason it’s meaningless is that time passes at different rates depending on your frame of reference. Gravity slows time. Velocity slows time.

“Time is an illusion. Lunchtime doubly so.” -Douglas Adams

The concept of evolution depends on some sort of time flow, or at least causality. You can’t claim we evolved the perception of time flow because to evolve something you need time flow.

No, I’m sure that St. Augustine would have no difficulty explaining pornography.

Discover isn’t so sure that time exists.

It’s from a letter he wrote on March 21st 1955 following the death of his old Bern sounding-board Michele Besso, just a few spare months before his own demise. Very much filled with a sense of mortality, it was a letter of condolence addressed to Besso’s son Vero and sister Bice. (For completeness, it’s currently still sparse entry in the Einstein Archives database.) Probably the passage’s highest profile appearance in the Einstein literature is Albrecht Fölsing using it as the concluding words of his (rather good) 1993 biography.

I’ve always taken it as broadly a reference to his discovery that whether events are simultaneous is observer dependent. If observers can’t agree about whether two events take place at the same time, that decisively undermines any simple notion of there being something they can all agree is “The Present”. And with it the notion of a universal split into past and future.

There’s then the more subtle aspect that Einstein came to think of spacetime as a four dimensional “thing” - something with a shape and something that had to be considered as a whole. In that view, spacetime and all the worldlines of particles within it is something static that just is. The perception of time flowing happens within this unevolving stucture. (Subsequently, Wheeler de-emphasised this way of thinking and started talking about geometrodynamics.)

That’s the way we perceive it, but I think the idea here is that time doesn’t “flow”, but that as we move from point A to point B in time, we are simply seeing another aspect of the universe, as you would if you travel from point A to point B in space. Like that old story about looking at an elephant. You see a trunk, but then walk around to the other side and you see a tail. The elephant didn’t change; your perspective did. Or walk away from the elephant - it looks smaller. Did walking away cause it to get smaller? My understanding of this idea is that time and causality reflect something that is real, but the way we are perceiving them is an illusion.

I’m no physicist. Never played one on TV, either. Never got past algebra and trigonometry in high school. But. . .

If we know that entropy always increases, and that this has been going on since the beginning (putting aside the issue of what beginning means in this context) of the universe, isn’t time the direction in which entropy increases?

So if there is X amount of entropy (not that I’m implying that entropy can be measured – I have no idea) at a given point, and Y (Y being greater than X) at another, we’d say that point Y comes after point X. Time being our understanding of the difference between point X and point Y.

I know, this probably doesn’t make any sense whatsoever.

Another relevant Douglas Adams quote (well, paraphrased from memory) “Time is an illusion to explain the passage of history. History is an illusion to explain the passage of time.”

Right, but I was referring to modeled evolution, rather than observed evolution. You can model evolution in a spreadsheet as long as you can advance to the next cell without needing much more than selective pressures and random variations. In other words, our perception of causality may be an illusion, but our perception of arithmetic is all there is to arithmetic.

That’s a start. But you can also have two different locations in the Universe at the same time (however you define “same time”) which also have different entropies, and you can’t say from that that one of those comes after the other. But the notion of entropy is closely related to the notion of causality, and you can use causality to establish a notion of “past”, “present”, “future”, and “elsewhere”. Note the four categories there, instead of three: In relativity, “present” is a single point, “past” is the set of all events (points in spacetime) which can causally effect that point, and “future” is the set of all events which can be causally effected by that point, but there’s a whole lot of the Universe which isn’t causally connected to the “present” at all.


Evolution is the description of behavior of any system that has change and non-random removal/selection/redistribution. For example, put twenty random integers into the first row of a spreadsheet. Now generate new rows by applying the following rule: Row N+1 is identical to Row N except for:
– From one to three cells containing odd integers in Row N are not put into Row N+1
– From one to three new cells are added to Row N+1 by multiplying any two cells from Row N together.

You will see that you’ll get more and more even numbers. It’s evolution. It’s not biological evolution but it’s still an example of evolution, not a model of evolution. Being an abstract concept, the only thing that is required is some change over time and selective pressure. Almost anything you put on a piece of paper about gravity is going to be a model of gravity, not an example of gravity – which brings us back to my original point. Evolution is a complete concept that is based on our model of time flow, which can be an illusionary echo of some actual more complex or different time flow. It can be used to model observed biological evolution that might be subject to actual complex or different time flow.

:frowning: I don’t think I can express myself that well right now. I’m too tired. Sorry.