# What is Time?

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Some great posts guys,

What about a "Moment in Time" do we ever reach one?, my point being once you think you have reached a point in time it is already gone. A sort of a paradox if you like.

It's like ''now'' isn't ''now'', it's now ''before''

An interesting fact in relativity is that there is no such distinction between the past and future --- indeed, it seems such concepts don't really exist, which can seem at odds with the way we tend to look at the world.

If time exists, then there can only be the present time which holds any significance for systems. The only time which ever exists, is the present time, so perhaps thinking of it this way, a moment in time is always the present time, nothing truly exists ''before'' - which is quite an odd notion since we humans are capable of recording events and sense time ''pass us by'' along with the event, but it is for this reason why might think the ''sense of time'' is purely something our brains creates. There is certainly plenty evidence that our sense of time is in fact created by two specific long-term and short-term gene regulators. So maybe, just to keep us from insanity, our evolution took a path to believe that there was a real order to events by having a sense of time.

I'm curious about something so please bear with me. Have you never heard the term space used in any other sense than "place inside a room"? For example when you hear the term Hilbert Space as being a function space, what did the term space mean to you?

Wikipedia defines Space in the mathematical sense as follows

To me, a space is just a degree of freedom, of course my mind seems somewhat at odds with that when you think of a Hilbert Space, which could just be a point... in fact, people tend to think that $\psi$ is some point on a Hilbert Space $H$. So I don't know... I guess a space means somewhere with some kind of length and width. Wikipedia's explanation is very mathematical in its use of defining space, but it is perhaps truer.

I guess you could say, ''I have a simple understanding of what a space is''.

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If time exists, then there can only be the present time which holds any significance for systems. The only time which ever exists, is the present time, so perhaps thinking of it this way, a moment in time is always the present time, nothing truly exists ''before'' - which is quite an odd notion since we humans are capable of recording events and sense time ''pass us by'' along with the event, but it is for this reason why might think the ''sense of time'' is purely something our brains creates. There is certainly plenty evidence that our sense of time is in fact created by two specific long-term and short-term gene regulators. So maybe, just to keep us from insanity, our evolution took a path to believe that there was a real order to events by having a sense of time.

Yes this is the point (the link between time and existence) I am trying to get across but it is fundamentally at variance with the notion of a spacetime manifold.

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To me, a space is just a degree of freedom, of course my mind seems somewhat at odds with that when you think of a Hilbert Space, which could just be a point... in fact, people tend to think that $\psi$ is some point on a Hilbert Space $H$. So I don't know... I guess a space means somewhere with some kind of length and width. Wikipedia's explanation is very mathematical in its use of defining space, but it is perhaps truer.

I guess you could say, ''I have a simple understanding of what a space is''.

I believe that if you were to think of it simple as a set then you'd bve safe. Hilbert space is a set of functions. I'm just trying to get ytou to understand the difference between physical space a mathematical space.

When I was in college studying to become a physicist I saw that if I took manth courses instead of basket weaving I could have a second majopr in math. And with physics you can't have enough math. That's why I'm familiar with mathematical spaces.

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I believe that if you were to think of it simple as a set then you'd bve safe. Hilbert space is a set of functions. I'm just trying to get ytou to understand the difference between physical space a mathematical space.

When I was in college studying to become a physicist I saw that if I took manth courses instead of basket weaving I could have a second majopr in math. And with physics you can't have enough math. That's why I'm familiar with mathematical spaces.

Yes, I saw your posts. I thought they had been well written.

Yes this is the point (the link between time and existence) I am trying to get across but it is fundamentally at variance with the notion of a spacetime manifold.

I think with the manifold, one has to remember that if we consider time as a very good instrument to help us measure things, then it works quite well. How do you get someone to be convinced that time doesn't really exist, only the experience of time exists?

Relativity might have at it's core the manifold which interconnects space and time together, but at the heart of relativity, time doesn't even exist! It vanishes from the equations and in general relativity, the motion of systems aren't even represented by true time evolution's - motion arises as a symmetry of the theory. Worldline's are static as well, so there is no past or future; so for a theory which successfully united time and space into the same manifold, it kind of makes a mockery of times existence simultaneously.

I believe that if you were to think of it simple as a set then you'd bve safe. Hilbert space is a set of functions. I'm just trying to get ytou to understand the difference between physical space a mathematical space.

When I was in college studying to become a physicist I saw that if I took manth courses instead of basket weaving I could have a second majopr in math. And with physics you can't have enough math. That's why I'm familiar with mathematical spaces.

I certainly couldn't add anything more to your posts. Though I'd like to ask you, do you consider there being more to a space than thinking of it as a degree of freedom?

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Please excuse my ignorance, as I know nothing about this subject and enjoy reading the discussions. It's just that I read somewhere that we're travelling through time at a certain rate (equivalent to the speed limit of the Universe - light speed?) and, according to some principle which states you can only move in one direction at once, before a change of direction through one axis is minused from the speed of your trajectory on the other axis, thus, as we travel through space, our velocity(?) through space is deducted from that of our speed(?) through time.

Before anyone laughs, please note, the question marks are there to hopefully demonstrate I don't think we 'travel through time' at any 'speed' but some mathematical equivalent of that idea.

If I've got ANY of that right (which I don't doubt I've made a complete mess of explaining) would it explain time dilation?

Edited by Abecedarian
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How do you get someone to be convinced that time doesn't really exist, only the experience of time exists?

You can't. Different people have their own ideas of what time is all about. I explained mine already when I used the analog with the electric field.

It vanishes from the equations ..

I strongly disagree. Consider the Lorentz force equation

$\frac{dp^{\alpha} }{d\tau} = \frac{q}{c} F^{\alpha\beta} U_{\beta}$

That has time explicitly in it.

and in general relativity, the motion of systems aren't even represented by true time evolution's - motion arises as a symmetry of the theory. Worldline's are static as well, so there is no past or future;

Worldlines are a set of variables which determines a curve. One of those variables is time.

I certainly couldn't add anything more to your posts. Though I'd like to ask you, do you consider there being more to a space than thinking of it as a degree of freedom?

Yes. I don't think of space as beng a degree of freedom. The number of parameters required to uniquely specify the system is called the number of degrees of freedom. The system that those numbers are decribing isn't a degree of freedom.

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I am getting confused as to which thread I said what in however I'm sure I said somewhere words to the effect that if you wish to appeal to (modern) mathematics for support and proof you have to remain within the conditions of validity.

For manifolds each point either exists or it doesn't. You can't have points popping in and out of existence, just because you don't use them.

Further you need to state whether you are using manifold in the general sense as just a collection of elements of a set. This definition possesses a very limited mathematical structure.

Or in the specific sense of a topological manifold where you can take advantage of significant mathematical structure, up to and including calculus and beyond.

Edited by studiot
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Further you need to state whether you are using manifold in the general sense as just a collection of elements of a set.

I disagree. First off its the context which tells you what the manifold is. Second, quite often when one uses the term manifold its because they want to emphasize that its not physical space.

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I strongly disagree. Consider the Lorentz force equation

$\frac{dp^{\alpha} }{d\tau} = \frac{q}{c} F^{\alpha\beta} U_{\beta}$

That has time explicitly in it.

The time vanishing from GR is a result of quantizing the EFE equations and out of which you get the Wheeler de Witt equation, which is the timelessness one speaks about at the heart of GR.

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If the points of a manifold don't exist, the manifold doesn't either.

For functions defined on the manifold you can apply restrictions such as for X1 <0 f is not defined (not zero, not defined which is different)

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The time vanishing from GR is a result of quantizing the EFE equations and out of which you get the Wheeler de Witt equation, which is the timelessness one speaks about at the heart of GR.

That doesn't downplay the concept of time. Einstein's field quations are about defining a gravitational field. That field may vary with time and free particles which are in the field change their position as a function of time.

At this point in time I'm going to back out and leave it be. I've said all I've had to say and anything more would just be repetition. We'll just have to agree to disagree my friend.

Edited by pmb
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That doesn't downplay the concept of time. Einstein's field quations are about defining a gravitational field. That field may vary with time and free particles which are in the field change their position as a function of time.

At this point in time I'm going to back out and leave it be. I've said all I've had to say and anything more would just be repetition. We'll just have to agree to disagree my friend.

Julian Barbour takes it seriously. He has studied it for years and now believes that time does not exist.

The timelessness is considered a real problem for certain physicists and have dubbed it with a special name, called the ''Time Problem.''

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We just don't believe this is the case any more. One reason comes from relativity, if it is flowing, what is it flowing relative to? I will find you a paper which would shed some light on this perhaps.

Here

http://arxiv.org/abs/0812.0240

So I read the paper. Fascinating stuff, and it shows me that we still have a lot to learn about the deeper roots of the universe.

However, one of the ideas presented in this paper is not that time does not flow, but that time does flow, and that flow, as well as the arrow of time, are fundamentally tied into the universe at a quantum level.

Quantum physics introduces process, unpredictability, and an arrow of time: the flow of time is built into its deep nature

The author goes on to state that:

[O]ne should note that even when micro processes that take place are themselves time reversible, the actual even that happens occurs in one direction time...What actually occurs rolls on in a uni-directional way, even when the physics is time reversible.

Brian Green at least echoes the sentiment of there being a defined direction in time's flow in his book The Fabric of the Cosmos:

The arrow of time -- the fact that things start like this and end like that but never start like that and end like this -- began its flight in the highly ordered, low-entropy state of the universe at its inception.

Professor Greene goes on to say in the end notes for that section:

For example, why does electromagnetic radiation travel in expanding outward waves but not contracting inward waves, even though both are perfectly good solutions to Maxwell's equations of electromagnetism? Well, because our universe has low-entropy, coherent, ordered sources for such outward waves -- stars and lightbulbs, to name two -- ... [derived] from the even more ordered environment at the universe's inception...

Now, I grant that both the book and the paper are at least four years old. What prompted such a drastic shift in the mindset of the physics community between then and now to bring us to the conclusion that the flow of time does not really happen?

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So I read the paper. Fascinating stuff, and it shows me that we still have a lot to learn about the deeper roots of the universe.

However, one of the ideas presented in this paper is not that time does not flow, but that time does flow, and that flow, as well as the arrow of time, are fundamentally tied into the universe at a quantum level.

The author goes on to state that:

Brian Green at least echoes the sentiment of there being a defined direction in time's flow in his book The Fabric of the Cosmos:

Professor Greene goes on to say in the end notes for that section:

Now, I grant that both the book and the paper are at least four years old. What prompted such a drastic shift in the mindset of the physics community between then and now to bring us to the conclusion that the flow of time does not really happen?

George Ellis says at the very beginning that current theoretical physics states there is no flow to time. His paper simply makes an argument for the flow. My point to you was that mainstream really does believe there is no flow.

And I know many physicists take the arrow of time seriously, but I don't. Time isn't linear in the sense you can draw an arrow extending from somewhere. Time is really all about geometry.

George Ellis says at the very beginning that current theoretical physics states there is no flow to time. His paper simply makes an argument for the flow. My point to you was that mainstream really does believe there is no flow.

And I know many physicists take the arrow of time seriously, but I don't. Time isn't linear in the sense you can draw an arrow extending from somewhere. Time is really all about geometry.

Here's an excerpt out of an online book I am reading

"Time is a concept introduced specially to describe the flow of events around us; it does not itself flow, it describes flow. Time does not advance. Time is neither linear nor cyclic. The idea that time flows is as hindering to understanding nature as is the idea that mirrors Page 71 exchange right and left. The misleading use of the expression ‘flow of time’, propagated first by some flawed Ref. 36 Greek thinkers and then again by Newton, continues. Aristotle (384/3–322 bce), careful to think logically, pointed out its misconception, and many did so after him. Nevertheless, expressions such as ‘time reversal’, the ‘irreversibility of time’, and the much-abused ‘time’s arrow’ are still common. Just read a popular science magazine chosen at random.''

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George Ellis says at the very beginning that current theoretical physics states there is no flow to time. His paper simply makes an argument for the flow. My point to you was that mainstream really does believe there is no flow.

And I know many physicists take the arrow of time seriously, but I don't. Time isn't linear in the sense you can draw an arrow extending from somewhere. Time is really all about geometry.

I understand that as far as the equations are concerned, there really is no direction in time. They are equally valid whether time moves in a positive direction or a negative one. I don't have the math skills to use the equations, so I'll borrow an example from Greene again. He says that, based solely on the math of the equations, it is far more likely that a partially melted ice cube sprang into existence from a state of higher entropy (for instance a glass of water) than from a state of lower entropy (a completely frozen ice cube).

The question he goes on to ask is - why do we never see this happening, if there really is no flow to time? You have to admit, the idea of an arrow of time is a compelling one.

So what makes you, personally, accept the idea it's not a good explanation for what we experience (with the proviso, of course, that what we experience is not always the best measure of reality, as quantum mechanics so forcefully teaches us)?

Here's an excerpt out of an online book I am reading

I'll check that out - thank you again.

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I understand that as far as the equations are concerned, there really is no direction in time. They are equally valid whether time moves in a positive direction or a negative one. I don't have the math skills to use the equations, so I'll borrow an example from Greene again. He says that, based solely on the math of the equations, it is far more likely that a partially melted ice cube sprang into existence from a state of higher entropy (for instance a glass of water) than from a state of lower entropy (a completely frozen ice cube).

The question he goes on to ask is - why do we never see this happening, if there really is no flow to time? You have to admit, the idea of an arrow of time is a compelling one.

So what makes you, personally, accept the idea it's not a good explanation for what we experience (with the proviso, of course, that what we experience is not always the best measure of reality, as quantum mechanics so forcefully teaches us)?

Well sure, the ice cube example obeys thermodynamical laws. Is the arrow of time a concept which is being abused to explain something which has completely valid reasons for its existence and the way it behaves?

It's certainly not redundant to think an ice cube came from a higher state of entropy because of the thermodynamic laws? Why would one need to talk about something like an ''arrow to time''?

Of course, entropy is often the reason we may think there is some kind of directionality to time. Direction is meaningless inside the context of the equations, it only makes meaning when recording devices (like our brains) measure events unfold. Then the idea of time becomes somewhat meaningful. Put it another way, in relativity, time arises because of moving pieces of matter acting like clocks. There was a period in the universe called the radiation era where no matter existed - this existed before matter appeared in the universe - entropy existed then, but not in the kind of form where we can associate moving clocks. In this sense, is time really fundamental or is it really a by-product of slow moving systems?

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Hi Aeththelwulf

You said

It's like ''now'' isn't ''now'', it's now ''before''

An interesting fact in relativity is that there is no such distinction between the past and future --- indeed, it seems such concepts don't really exist, which can seem at odds with the way we tend to look at the world.

If time exists, then there can only be the present time which holds any significance for systems. The only time which ever exists, is the present time, so perhaps thinking of it this way, a moment in time is always the present time, nothing truly exists ''before'' - which is quite an odd notion since we humans are capable of recording events and sense time ''pass us by'' along with the event, but it is for this reason why might think the ''sense of time'' is purely something our brains creates. There is certainly plenty evidence that our sense of time is in fact created by two specific long-term and short-term gene regulators. So maybe, just to keep us from insanity, our evolution took a path to believe that there was a real order to events by having a sense of time

According what you said we might each exist in a perpetual "Now' with the past flowing passed us and the future coming towards us in an absolute even flow? Sort of we objects are effected by time, relative to the time flow to our repective perpetual "Nows"

Or have I completely misuderstood what you mean?

Edited by Alan McDougall
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Hi Aeththelwulf

You said

According what you said we might each exist in a perpetual "Now' with the past flowing passed us and the future coming towards us in an absolute even flow? Sort of we objects are effected by time, relative to the time flow to our repective perpetual "Nows"

Or have I completely misuderstood what you mean?

What I think I am saying is that there is no past now, as there is no future later, we are all stuck in the present time and that never changes, so we might think we live in a type of eternal present frame - and it will be this present time which changes, there is nothing flowing in or out of the present sphere of time.

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Please excuse my ignorance, as I know nothing about this subject and enjoy reading the discussions. It's just that I read somewhere that we're travelling through time at a certain rate (equivalent to the speed limit of the Universe - light speed?) and, according to some principle which states you can only move in one direction at once, before a change of direction through one axis is minused from the speed of your trajectory on the other axis, thus, as we travel through space, our velocity(?) through space is deducted from that of our speed(?) through time.

Before anyone laughs, please note, the question marks are there to hopefully demonstrate I don't think we 'travel through time' at any 'speed' but some mathematical equivalent of that idea.

If I've got ANY of that right (which I don't doubt I've made a complete mess of explaining) would it explain time dilation?

Basically, yes. There is what is called a velocity four-vector, with the components being the three spatial velocity components and the fourth being time (multiplied by c). The magnitude of the vector is the speed of light, and it's invariant. So if you have a spatial velocity, the time component also changes to compensate; that's time dilation. (In your own frame, you are at rest, so you see time passing normally.)

Thank you.

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Thank you.

Note: A photon doesn't have a 4-velocity. A 4-vlocity requires dividing by a proper time interval on the photons world line and that's always zero, hence there's no 4-velocity for photons (or any other luxon).

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Hi

What is time?

Depending on the context? A coordinate or a parameter.

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First of all time is not 3 dimensional, it exists in a 4th dimension called space-time.

Secondly, time can be viewed in a number of ways, not just in one. Here are a couple.

Time can represent the amount of decay ore chaos. One could argue that entropy is a measure of time because everything deteriorates and gets more chaotic as time passes because the universe loves to increase its entropy. Ergo time is just a measure of chaos. (This next segment is just my own wondering) This could also show how time started when the big bang occurred; first there was total-nothingness, then an explosion and here we are.

Time could also be seen as the measure of an object giving off light. Since light is the fastest thing in the universe (or at least we think it is), it is safe to say that time travels at the speed of light.

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There are consequences to this view that you may not have appreciated.

Take a 12 inch ruler.

Choose a coordinate system so that the ruler extends from a to a+12 inches along one (spatial) axis.

We say that the extent of the ruler is 12 inches.

If we look at the endpoints with sufficient magnification we see that they are less well defined.

Now let us consider the time axis.

The ruler comes into existance at time t and is consumed by fire 1 year later so the ruler has a duration in time of t+1 years.

The temporal end points will again be more blurred under closer examination.

Would you agree with this?

Hi, I am very sorry that I overlooked your comment in another post to look at post 25# of yours!

I agree we never really reach a moment in time, just when we think we have the next moment is already there. There is always a blur at both ends no matter how close one observes them. I once wrote a short paper on the subject, however, I used an arrow and how it flies toward its target always a blur like you say, I rationalized this by saying the movement of the arrow was like infinitely tiny frames on a movie reel, jumping between moments rather than a smooth flow through the air like the flow of a river.

If we stand still relative to the universe, time still moves , but once a person starts to move relative to the universe, time slows, this effect of course can only be seen in a meaningful way at colossal speeds approaching the of the speed of light.

Some physicists say, however, that there is no real "Arrow of Time" or that time flows smoothly like a river, but time is in reality infinity of separate infinitively tiny moments, extending back to the eternal past and into the eternal future, in both directions from the moment we exist in the present. To understand the theory of infinitely of moments making up the reality of the universe, think of a loaf of bread as the universe and each grain of wheat in the loaf (universe) as a moment or “Now” somewhere in the universe?.

The Left side of the loaf the moment of creation the right into the Infinite future

Loaf or universe

Big Bang =Past<.................................<NOW>.............................................................> Future

Someone on the other side of the universe, directly opposite, could exist in very the same “NOW” moment as you are. Like slicing the loaf directly in front of you are linking with every other “”NOW” across the time frame you exist in across the whole universe Thus a universal “NOW” exist across the in the universe at that moment! However the very next moment the "NOW’s” no longer agree and you must make another slice to see what is happening at the other end of the universe, because the “NOW’ moments jump to different “NOWS” because of the effect of gravity, mass, speed and relativity

However, if you were to slant your hypothetical knife to the left across the universe, which is towards the past from your vantage moment in time” you would hypothetically be able to view what, is going on in the “NOW” moment in the past for of the object you first viewed in the same moment or “NOW” that was in sync originally with your original moment or “NOW”.

You would be looking at the past of the far off object. Your “NOW’ and its “NOW” would differ in time and space. You would continue to exist in the ever-jumping subjective “NOW” but could look into the past of the object in its objective “NOW”.

The same will happen if you took the hypothetical knife, sliced the loaf or universe to the right, toward the future, then you will be able to observe what is going on in the future of the objects “NOW” future.

thus, every moment that has ever existed from the very beginning of its existence until its end be it heat death or infinite eternity past, to the present, to the infinite future still exists in our universe and the law’s of physics cater for that fact

Regards

Alan

Edited by Alan McDougall
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• 2 months later...

Time be the Now early later zone move and recordance

What do you suppose about that

Thanks

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