The Illusion of Time

[JonG]

I just want to make a brief note on something that has cropped up a various points within this thread : - is this Physics or Philosophy?

 

There is a well known book on the subject of Time entitled "About Time" by Paul Davies, who is a physicist. He has clearly been fascinated by the topic throughout his life and there are aspects of it that could well be described as Philosophy rather than physics. But the impact that Physics has had on this subject, largely due to the theories of relativity, is very significant so it is no surprise that there is overlap between ideas which might be described as Physics and others which might be described as Philosophy.

 

The crux of the problem appears to be in reconciling two very different notions about time. One is the personal, everyday, usage of the concept; viz that time is characterised by a present, past and a future together with the idea that time is something which flows. The other is time as it appears in Physics;- a coordinate, similar to, but not the same as, a spatial dimension. In this view, sometimes referred to as "block time", there is no place for notions such as past, present and future, nor can any meaning be attached to the idea that time flows. These two views of time are very different and, not surprisingly, of interest to some physicists and some philosophers.

 

Personally, I don't find it at all odd that someone should want to discuss these differences on a Physics forum (or on a Philosophy forum as well).

Edited October 1, 2014 by JonG

[MigL]

There is a small but non-trivial difference between the three spatial dimensions and the time dimension.

This leads to some confusion as to the existence of time.

 

While we can measure separation directly in any of the three spatial dimensions simply by laying down a measuring tape between two co-ordinates, we cannot do the equivalent in the time dimension. The difference is that we only ever have access to the local present. The past is gone and the future hasn't happened yet, so direct measurement between two co-ordinates is impossible.

Our only option is indirect measurement using properties that change over time. If we consider the property of position, then the resultant change over time, is motion. But other properties may be used.

 

This does not mean that time is illusionary or equivalent to motion.

Time is a certainly valid concept, and until there is proof otherwise, I, for one, will assume it is real.

[swansont]

Or, viewed a little differently, in any non-static system a state change (not just position) requires an additional orthogonal variable to uniquely describe the system. We do this with time. Unless your alternate solution can eliminate the need for this variable, it basically reduces to semantics. (you don't eliminate time, you just replace it with something else. So, big deal)

[JonG]

It's difficult to see how time can be considered to be an illusion, as it is necessary to describe what we see about us. However, there is a case for regarding such concepts as "the present" or "flow of time" as illusory simply because there is no objective evidence for their existence. Even then, "illusory" might be seen as harsh. Perhaps they should just be labelled as subjective - notions within our heads.

[Dr. Funkenstein]

Time is a measurement of man brought about to put some order to seasonal change, and perhaps rivers ebbs and overflows. Beyond usefulness to mankind it has no bearing. How it relates to change is a mystery to me, from a pure physics perspective, "What has ever changed, from one thing into something totally different?"

[swansont]

Time is a measurement of man brought about to put some order to seasonal change, and perhaps rivers ebbs and overflows. Beyond usefulness to mankind it has no bearing.

 

One could make the same argument for length, width and height, but people rarely seem to do that.

[jibefan]

in regard to MIGL's post, "the past is gone". The past is Never gone. The past is recorded in the cosmos. As we peer further into the universe, we see further into the past.

[swansont]

in regard to MIGL's post, "the past is gone". The past is Never gone. The past is recorded in the cosmos. As we peer further into the universe, we see further into the past.

 

We can't peer into our own past, which is what I think the point was.

[JonG]

By Dr Funkenstein:

Time is a measurement of man brought about to put some order to seasonal change, and perhaps rivers ebbs and overflows. Beyond usefulness to mankind it has no bearing.

By swansont:

 

One could make the same argument for length, width and height, but people rarely seem to do that.

That could be because we perceive length in a way which is similar to the way in which it is represented in Physics. However, our perception of time is quite different. We don't perceive time as a point, or series of points, on an axis, as it is represented in space-time, but as some mysterious flowing entity which is carrying us along with it. The latter view of time, although it now sounds far-fetched from a scientific perspective, is similar to Newton's "absolute time".

 

"Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external,"

Edited October 2, 2014 by JonG

[swansont]

By Dr Funkenstein:

 

That could be because we perceive length in a way which is similar to the way in which it is represented in Physics. However, our perception of time is quite different. We don't perceive time as a point, or series of points, on an axis, as it is represented in space-time, but as some mysterious flowing entity which is carrying us along with it. The latter view of time, although it now sounds far-fetched from a scientific perspective, is similar to Newton's "absolute time".

 

"Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external,"

 

I think it's absolutely about perception; when it comes down to the actual arguments, there seems to be no reason for time to be singled out in terms of its status as a concept.

[JonG]

By swansont.

 

 

I think it's absolutely about perception; when it comes down to the actual arguments, there seems to be no reason for time to be singled out in terms of its status as a concept.

I agree that the differences in how we perceive time and spatial distances probably relate to the fact that we accept the scientific description of spatial matters without problems but are inclined to be puzzled by time.

 

However, there is a difference in the way time and spatial increments appear in the flat spacetime metric, but I am unsure how it relates to the matter being discussed. In the flat spacetime metric, the c²dt² term is opposite in sign to the spatial terms.

 

ds² = -c²dt² + dx² + dy² + dz².

 

But it's hard to imagine what things would be like if there wasn't this difference in sign, and I am not sure that it has any bearing on how we perceive time.

[elfmotat]

By swansont.I agree that the differences in how we perceive time and spatial distances probably relate to the fact that we accept the scientific description of spatial matters without problems but are inclined to be puzzled by time.

However, there is a difference in the way time and spatial increments appear in the flat spacetime metric, but I am unsure how it relates to the matter being discussed. In the flat spacetime metric, the c²dt² term is opposite in sign to the spatial terms.

ds² = -c²dt² + dx² + dy² + dz².

But it's hard to imagine what things would be like if there wasn't this difference in sign, and I am not sure that it has any bearing on how we perceive time.

You can change variables [math]t \to it[/math] and the metric becomes positive-definite. We're more than free to define the quantity [math]it[/math] as "time." In fact this little trick can enormously simplify lots of problems in physics, for example the integral in my signature.

[JonG]

You can change variables [math]t \to it[/math] and the metric becomes positive-definite. We're more than free to define the quantity [math]it[/math] as "time." In fact this little trick can enormously simplify lots of problems in physics, for example the integral in my signature.

I am aware of the "neatness" of replacing t by it, however, doing so also makes the speed of light, together with other things, imaginary numbers. I don't think we are as free to make such changes as you suggest. The t which appears in "it" is not the t which would represent time as we know it.

[swansont]

I am aware of the "neatness" of replacing t by it, however, doing so also makes the speed of light, together with other things, imaginary numbers. I don't think we are as free to make such changes as you suggest. The t which appears in "it" is not the t which would represent time as we know it.

 

This is physics, though. Not all variables in equations have physical significance; we sometimes use complex numbers and then only look at the real part, or find that squaring it is the physically significant term. If it is useful, someone will use it.

[JonG]

 

This is physics, though. Not all variables in equations have physical significance; we sometimes use complex numbers and then only look at the real part, or find that squaring it is the physically significant term. If it is useful, someone will use it.

 

 

I am not clear what is being stated here. The point is that spatial intervals and time intervals do not appear in the metric in the same way - the relevant terms differ in sign. Replacing [math]t[/math] by [math]it[/math] doesn't change this because the [math] t [/math] which appears in [math]it[/math] isn't what we consider to be time - it is an imaginary number. To avoid confusion, [math]t[/math] should be replaced by something like [math]it'[/math] to make it explicit that [math]t[/math] and [math]t'[/math] are not the same.

 

(Imaginary time has been conjectured as a possibility for the early universe, but I don't think anyone considers that time as we know it now ,rather than at the Big Bang, is imaginary.)

[elfmotat]

 

 

I am not clear what is being stated here. The point is that spatial intervals and time intervals do not appear in the metric in the same way - the relevant terms differ in sign. Replacing [math]t[/math] by [math]it[/math] doesn't change this because the [math] t [/math] which appears in [math]it[/math] isn't what we consider to be time - it is an imaginary number. To avoid confusion, [math]t[/math] should be replaced by something like [math]it'[/math] to make it explicit that [math]t[/math] and [math]t'[/math] are not the same.

 

(Imaginary time has been conjectured as a possibility for the early universe, but I don't think anyone considers that time as we know it now ,rather than at the Big Bang, is imaginary.)

 

Lots of people have suggested that it is more "fundamental," in a sense, than t, and that all of the strange minus signs and imaginary numbers in relativity and QM can be explained away by the idea that we're "accidentally" using a Wick rotated dimension in all of our equations. The most notable proponent of this idea is Hawking.

 

Semi-related:

[michel123456]

By Dr Funkenstein:

By swansont:

That could be because we perceive length in a way which is similar to the way in which it is represented in Physics. However, our perception of time is quite different. We don't perceive time as a point, or series of points, on an axis, as it is represented in space-time, but as some mysterious flowing entity which is carrying us along with it. The latter view of time, although it now sounds far-fetched from a scientific perspective, is similar to Newton's "absolute time".

 

"Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external,"

I wrote it down on several places on this Forum:

_you can easily replace the concept of "flowing time" with the reverse concept of "displacement through time".

Etienne Klein has asked the question before I did: does time flow or do we travel through time?

 

Simply consider that all objects travel into an immovable substrate called time, not so different than the substrate we call space.

Or to put it differently:

 

If one accepts that objects can change position in space, if one should accept that space alone does not stand but that the correct situation is that objects can change position in the Spacetime continuum, then the result is that objects can displace both in space & time.

And as a consequence, there is no "flow" of time, there are objects changing coordinates in spacetime.

Edited October 4, 2014 by michel123456

[JonG]

I wrote it down on several places on this Forum:

_you can easily replace the concept of "flowing time" with the reverse concept of "displacement through time".

Etienne Klein has asked the question before I did: does time flow or do we travel through time?

 

Simply consider that all objects travel into an immovable substrate called time, not so different than the substrate we call space.

Or to put it differently:

 

If one accepts that objects can change position in space, if one should accept that space alone does not stand but that the correct situation is that objects can change position in the Spacetime continuum, then the result is that objects can displace both in space & time.

And as a consequence, there is no "flow" of time, there are objects changing coordinates in spacetime.

 

 

I think that most people who have thought about this will have concluded that time is not "flowing", but that we are moving through time. There isn't a defnitive version of the idea because it is will inevitably be related to the working of human consciousness, and there isn't yet a clear understanding of how consciousness works.

 

Lots of people have suggested that it is more "fundamental," in a sense, than t, and that all of the strange minus signs and imaginary numbers in relativity and QM can be explained away by the idea that we're "accidentally" using a Wick rotated dimension in all of our equations. The most notable proponent of this idea is Hawking.

 

 

 

Just to prevent the discussion going off at a tangent I will reiterate the point I was originally making.

 

If dt represents an increment in time and dx, dy, and dz represent spatial increments, the flat spacetime metric (or Minkowski metric) is:

 

ds² = -c²dt² + dx² + dy² + dz²

 

which shows that the temporal term differs from the spatial terms in that it has a negative sign in front of it.

 

Is that true or isn't it?

 

Replacing t by it would give;

 

ds² = c²dt² + dx² + dy² + dz²

 

Is it being suggested that this version of the metric is true? (True now, not what is conjectured to have been the case shortly after the Big Bang).

Edited October 4, 2014 by JonG

[michel123456]

 

 

I think that most people who have thought about this will have concluded that time is not "flowing", but that we are moving through time. There isn't a defnitive version of the idea because it is will inevitably be related to the working of human consciousness, and there isn't yet a clear understanding of how consciousness works.

I don't think it is a good idea to slip into philosophy and questions about human consciousness.

We can stick to physics.

 

 

"Moving" is a concept that we use to describe a change in coordinate in space. Relativity states that motion also need time.

Thus, motion is something that takes place both in space & in time: in Spacetime.

 

The problem is that the currently accepted concept of "motion in time" is completely different with the concept of "motion is space".

 

Motion in space is understood as a change of coordinates.

"Motion" in time (duration) is commonly understood as an extension of the object. In a spactime diagram an object displacing through time is a line. IOW "motion" in time is understood as an object occupying many temporal coordinates.

 

Which is very different from a displacement in space.

That is why I believe it is wrong. i believe that motion in space and "motion" in time are exactly of the same nature: it is in both case a change of coordinates.

Edited October 4, 2014 by michel123456

[studiot]

You need to do the back substitution after the calculation to return from 'imaginary time' it to our time t.

 

see

 

http://en.wikipedia.org/wiki/Wick_rotation

 

and also

 

http://en.wikipedia.org/wiki/Imaginary_time

Edited October 4, 2014 by studiot

[JonG]

I don't think it is a good idea to slip into philosophy and questions about human consciousness.

We can stick to physics.

 

 

 

 

Philosophy!!! What are you referring to?

You need to do the back substitution after the calculation to return from 'imaginary time' it to our time t.

 

 

 

If you make a substitution t = it' (i.e. t' = -it) and after substituting t = it' you do a back substitution t' = -it, you will end up with exactly the equation you started with.

 

ds² = -c²dt² + dx² + dy² + dz²

 

Edited October 4, 2014 by JonG

[michel123456]

You need to do the back substitution after the calculation to return from 'imaginary time' it to our time t.

 

see

 

http://en.wikipedia.org/wiki/Wick_rotation

 

and also

 

http://en.wikipedia.org/wiki/Imaginary_time

I thought it was commonly accepted that time is a dimension perpendicular to space.

 

If it is correct, then imaginary time IS space.

 

 

Philosophy!!! What are you referring to?

Sorry for that. Skip it.

Edited October 4, 2014 by michel123456

[studiot]

 

If it is correct, then imaginary time IS space

 

Not necessarily.

 

Operation by the operator i is equivalent to a rotation by pi/2.

 

So i operating on anything will produce an orthogonal axis.

 

Just as x,y,z and ct are orthogonal to each other, cit is orthogonal to all of them.

[michel123456]

 

Not necessarily.

 

Operation by the operator i is equivalent to a rotation by pi/2.

 

So i operating on anything will produce an orthogonal axis.

 

Just as x,y,z and ct are orthogonal to each other, cit is orthogonal to all of them.

It's a 5th dimension then.

[elfmotat]

Just to prevent the discussion going off at a tangent I will reiterate the point I was originally making.

 

If dt represents an increment in time and dx, dy, and dz represent spatial increments, the flat spacetime metric (or Minkowski metric) is:

 

ds² = -c²dt² + dx² + dy² + dz²

 

which shows that the temporal term differs from the spatial terms in that it has a negative sign in front of it.

 

Is that true or isn't it?

 

Of course it's "true."

 

 

 

Replacing t by it would give;

 

ds² = c²dt² + dx² + dy² + dz²

 

Is it being suggested that this version of the metric is true?

 

It's unclear what you mean by "true." All you did was change variables. It still physically represents the same thing. As long as your functions are analytic (which they usually are), you're free to make any variable complex. Both equations are "true." Let's define T=it. Then the metric (in 1+1 dimensions) is:

 

[math]ds^2= -dt^2+dx^2= dT^2+dx^2[/math]

 

We're now completely free to define the variable T as "time." In other words, the numbers we read on clocks are no longer called "time." Instead, we read a number off a clock and we multiply that number by i to get time. If we define things in this way then the metric is positive definite, and time is no different from any of the other dimensions. Plus, we get the added bonus that a lot of physics becomes much simpler.

 

Which variable is more fundamental: t or T? Your instinct might be to say, "well obviously t is more fundamental." But why? If we interpret the numbers on clocks as "distances measured in an imaginary dimension," then T is a real number and t is imaginary.

 

 

 

 

(True now, not what is conjectured to have been the case shortly after the Big Bang).

 

I don't know what you mean by this. Why would our ability to change variables depend on how long after the big bang we waited?

It's a 5th dimension then.

 

it is not independent of t, so it's not an additional dimension. If we know t then we know it.