Basic understanding of time

[Schneibster]

 

Yes, I know it's a dimension. And I agree it is a dimension of the same thing (spacetime) as the spatial dimensions are dimensions of, just as the up down dimension of a box and the back front dimension and the side-to-side dimension are all dimensions of the same thing - the box. But the time has different units, is what I'm saying. We have units of length (e.g. light-seconds) on the spatial axes and units of time (e.g. seconds) on the time axis.

 

Are you disputing this? If not, then we're cool. If you are, then we disagree.

 

Well, this time I can't complain you weren't precise or accurate. However, while I agree that we use different units, I do not agree that we must use different units.

 

Newtonian/Galilean physics insists that space and time are different things. Relativity, however, developed from Maxwell's equations that described electromagnetism, and that so clearly indicated the importance of c. Lorentz and Planck and all the rest went looking for the solutions that Maxwell had pointed the way to, and Einstein finally hit on the set of postulates that would support Maxwell's equations, and also describe Minkowski's spacetime, include Planck's units, and use Lorentz' transform; and eventually, even include Poincare's symmetry. The genius of Einstein formed this incredible synthesis that has defined modern classical physics and that will guide the formation of dimensional theories for generations to come, no doubt. String theory is a direct outgrowth of relativity, and shares both the complexity and the beauty of its progenitor.

 

So you may tell me if we "disagree."

Edited February 24, 2014 by Schneibster

[Lizzie L]

Well, that all sounds wonderful Schneibster, but you have not persuaded me that a light-second is the same as a second; that the speed of light is a second per second (as opposed to a light-second per second), that there is a "speed of time"; or that we are travelling through time at lightspeed!

 

But all the other stuff sounds fine.

[Schneibster]

Well, that all sounds wonderful Schneibster, but you have not persuaded me that a light-second is the same as a second;

Do you not believe a light-second of space is equivalent to a second of time, despite what the Lorentz transform tells you? Do you still not believe the math?

 

If we're being really rigorous I'd say a light-second of space is equivalent to a second of time in the limit of v or s approaching 0.

 

that the speed of light is a second per second (as opposed to a light-second per second), that there is a "speed of time"; or that we are traveling through time at light speed!

 

But all the other stuff sounds fine.

It's all implicit in Special Relativity, and even in Minkowski space and the Lorentz transform that predate it.

 

Lizzie I've known this for thirty-five years. I'm not trying to embarrass you but when did you find out the Lorentz transform is the correct transform for relativistic particles? How old were you? I was fifteen.

Edited February 24, 2014 by Schneibster

[mooeypoo]

 

Well, I'm finding I'm laboring the point so much it's maybe coming over as less trivial than it actually is! I'm not saying that change is time or time is change. I'm saying that time only makes sense in terms of change - if nothing changes, there's nothing to happen along the time axis! Furthermore, our current working definitions of time units seem to be in terms of actual physical oscillators. So if we were to imagine a world without change, it would also be a world without time. Although looking at it from our changing world, it would be just a very boring world!

 

But the reason it might be important it seems to me is that change can be reversible or irreversible. And if time is linked in some deep sense to change, the irreversibility of some changes would also give time a single direction. Which it seems to have. At least from our decaying world

Yes, I think I understand you, but I think it's the other way around. Change is defined by time, and not the other way around.

 

Clearly, we're arguing semantics, but the entire point of "defining" things falls on semantics, which is why it seems we're going into the nitpicky realm. Just to be clear: I'm enjoying this discussion tremendously. I hope you don't see any of my nitpicky comments as anything other than attempts to sort out the ideas properly.

 

I am starting to think that time might not be able to be properly defined outside the scope of its usage. That is, I think we, as limited human beings, intercept the universe in a certain way where we had to define things we observe. Space and time were aspects we had to define so we can continue to describe reality. Then, we found that they're very much related, and started to refer to them as spacetime -- but that's really a result of mathematical formulations that are based on what we initially defined: time and space.

 

So, we "made up" time and space as a descriptions for concepts that describes the behavior of the universe; I'm not too sure we can roll back the clock (time again!) to find an independent definition of time. It would likely become circular, as it seems to be now.

 

Does this make sense?

[Schneibster]

Lizzie, what I am telling you is in every good popular science physics book published in the last hundred years.

 

I really don't know what to say.

 

It's in every textbook too.

 

Maybe my textbooks are a bit out of date but do you really believe they're outright wrong? Do you know that little about the progress of physics over the last fifty years? We've all been waiting for the revolution, and it sputtered! String theory is all we got:

 

"My 'rents went to Berkeley and all I got was this crappy string theory T-shirt. "

 

Finally someone managed to incorporate supergravity into string theory at the dying end of the 20th century and called it "M-theory" mostly for membrane, but also for master. And there it has sat and rotted.

[hypervalent_iodine]

!

Moderator Note

Schneibster, you were warned about making insulting remarks about other members here. Since you continue to ignore that, you're being put on mandatory vacation for a week.

[Lizzie L]

Yes, I think I understand you, but I think it's the other way around. Change is defined by time, and not the other way around.

 

Clearly, we're arguing semantics, but the entire point of "defining" things falls on semantics, which is why it seems we're going into the nitpicky realm. Just to be clear: I'm enjoying this discussion tremendously. I hope you don't see any of my nitpicky comments as anything other than attempts to sort out the ideas properly.

 

I am starting to think that time might not be able to be properly defined outside the scope of its usage. That is, I think we, as limited human beings, intercept the universe in a certain way where we had to define things we observe. Space and time were aspects we had to define so we can continue to describe reality. Then, we found that they're very much related, and started to refer to them as spacetime -- but that's really a result of mathematical formulations that are based on what we initially defined: time and space.

 

So, we "made up" time and space as a descriptions for concepts that describes the behavior of the universe; I'm not too sure we can roll back the clock (time again!) to find an independent definition of time. It would likely become circular, as it seems to be now.

 

Does this make sense?

 

 

Yes indeed Nice to talk to you too.

[davidivad]

imagine if we were precise enough to measure time all the way down to the planck time. would or would that not be a basic unit of time. what i think time actually boils down to is your requirements of it. you use a hammer for a nail and a wrench for a bolt. there is more than one useful definition of time and each has its own advantage. isn't that great?

[Strange]

And I sort of agree, still. Units of time are defined in terms of clocks, and clocks involve oscillating things. A world without change would be a world without oscillators for a start - and I don't see that "time" would exist as a dimension in such a world.

 

The units we use to measure time are based on oscillation. That has nothing at all to do with the concept of time as a dimension, in for example, GR where the dimensions have nothing to do with change or oscillation.

 

But, as always, this discussion is pointless.

[michel123456]

IMHO the main obstacle in the discussion is that very few of us are ready to admit that time and space might be the one and same thing.

Schneibster may shout it another hundred times, the message will not be heard. That's because we are stuck with the obvious differences between time and space.

Like

(...)

 

But what seems more interesting to me is why time should be unidirectional, and the spatial dimensions bidirectional. And I think that has more to do with the way we think than anything "out there" in the world.

 

That is a very common difference.

But I think it is wrong to consider that there is such a difference. IMHO there is not.

Time is a single dimension that goes one-way: we call that "the arrow of time". Time is always positive.

Now, if you extract from 3D space one of the single dimensions of space, what do you get: you get distance.

And, surprise, distance is also always positive. There is no negative distance, as there is no negative time.

 

One will say then: how is it possible to take an object, displace it, and put it back in place? (something that you cannot do in time)

IMHO the only way to understand the consequence of Relativity, is to say that it is not possible to displace an object and then put it back in place. That's why I think we are mystified by space. We are blinded by something we feel is evidence, and Schneibster must be correct.

 

I am very sad. I hope he will come back.

Edited February 24, 2014 by michel123456

[swansont]

 

The units we use to measure time are based on oscillation. That has nothing at all to do with the concept of time as a dimension, in for example, GR where the dimensions have nothing to do with change or oscillation.

 

 

 

Indeed. I have no problem with saying we use change to measure time, but to say that time is change is a very different claim.

The OP said:

 

 

And I sort of agree, still. Units of time are defined in terms of clocks, and clocks involve oscillating things. A world without change would be a world without oscillators for a start - and I don't see that "time" would exist as a dimension in such a world.

Such a world is unattainable for us to study, so in that regard this is moot. It doesn't distinguish between change allowing time or time allowing change. It also doesn't acknowledge that the two could have a common cause, rather than being the same thing.

 

But what seems more interesting to me is why time should be unidirectional, and the spatial dimensions bidirectional. And I think that has more to do with the way we think than anything "out there" in the world.

The directionality of time is a separate issue. One of the more common notion is that it's related to entropy, which doesn't spontaneously decrease. If you want an unchanging universe, you need one with maximum entropy.

[StringJunky]

Indeed. I have no problem with saying we use change to measure time, but to say that time is change is a very different claim.

When you said earlier, paraphrasing, that time does not change the colder you make atoms, seems to me, to knock out the notion that time is change . ...if it was then an implication of that would be time is dependent on temperature - I've never read such a thing.

[I-try]

Lizzie L it is my understanding from your posts that you basic idea of our concept time is correct.

 

The human concept time becomes a part of that we refer to as reality, as also does a television transmitter or receiver”. That statement simply means that because we are an evolving product of the Universe provided with an intelligence that enables an awareness and curiosity regarding the universal environment, our intelligence, inventive abilities and concepts such as Time then become a small intrinsic portion of that we refer to as the Universe. In that regard, concepts such as fast, slow, velocity, acceleration, distance, space, time and so on and on to eventually become the concept we call reality. Then and only because of human ability to take and keep account does the human concept Time become a property of the physical portion of the Universe. The reality is there in the form of the precursors and magnitude of local parameters; the extent of reality being limited only by our ability to perceive and understand. The universe wide bewildering amount of relative movements – displacement - take place in conformity with the precursors and parameters active in individual local volumes. A collapsing star does so due to physical reality; we on the other hand have our concepts regarding the various stages prior to and responsible for the collapsing and aftermath that has required considerable investigation and written records.

Conclusion. The concept time is a necessary human concept that allows system, order and sequence by the division of our present and hoped for future reality of existence into small portion based on the duration of the precisely similar oscillation of atoms, that in turn take place in a minute volume of that we call space. The concept that we call Time is a fundamental dynamic reality forming a part of the universe and requiring the existence of intelligent beings to observe and take account.

[Lizzie L]

 

 

 

Indeed. I have no problem with saying we use change to measure time, but to say that time is change is a very different claim.

 

Yes, it would be, and it's not one I'm making

 

 

 

Such a world is unattainable for us to study, so in that regard this is moot. It doesn't distinguish between change allowing time or time allowing change. It also doesn't acknowledge that the two could have a common cause, rather than being the same thing.

 

Indeed, but as I understood it from an earlier post, such a world does emerge as a solution to Einstein's field equations. Did I misunderstand?

 

 

The directionality of time is a separate issue. One of the more common notion is that it's related to entropy, which doesn't spontaneously decrease. If you want an unchanging universe, you need one with maximum entropy.

 

 

Yes.

Lizzie L it is my understanding from your posts that you basic idea of our concept time is correct.

 

The human concept time becomes a part of that we refer to as reality, as also does a television transmitter or receiver”. That statement simply means that because we are an evolving product of the Universe provided with an intelligence that enables an awareness and curiosity regarding the universal environment, our intelligence, inventive abilities and concepts such as Time then become a small intrinsic portion of that we refer to as the Universe. In that regard, concepts such as fast, slow, velocity, acceleration, distance, space, time and so on and on to eventually become the concept we call reality. Then and only because of human ability to take and keep account does the human concept Time become a property of the physical portion of the Universe. The reality is there in the form of the precursors and magnitude of local parameters; the extent of reality being limited only by our ability to perceive and understand. The universe wide bewildering amount of relative movements – displacement - take place in conformity with the precursors and parameters active in individual local volumes. A collapsing star does so due to physical reality; we on the other hand have our concepts regarding the various stages prior to and responsible for the collapsing and aftermath that has required considerable investigation and written records.

Conclusion. The concept time is a necessary human concept that allows system, order and sequence by the division of our present and hoped for future reality of existence into small portion based on the duration of the precisely similar oscillation of atoms, that in turn take place in a minute volume of that we call space. The concept that we call Time is a fundamental dynamic reality forming a part of the universe and requiring the existence of intelligent beings to observe and take account.

 

Nice

[swansont]

 

Indeed, but as I understood it from an earlier post, such a world does emerge as a solution to Einstein's field equations. Did I misunderstand?

 

 

No, I don't think you did. Time exists in areas of empty space, so nothing in this physics demands that change be associated with time. It's required for the measurement of time, though, so we can't go there and measure the time under those conditions. There's also nothing that requires the idealized conditions of the equations actually exist; similarly we often talk of frictionless planes and elephants whose mass may be ignored in kinematics problems, but there's no implication that these are physically realizable.

[Lizzie L]

Just because it's bugging me - would you like to settle the argument as to whether a second and a light-second are the same thing in General Relativity?

 

And if the answer is yes - why ?

 

Thanks!

 

No, I don't think you did. Time exists in areas of empty space, so nothing in this physics demands that change be associated with time. It's required for the measurement of time, though, so we can't go there and measure the time under those conditions. There's also nothing that requires the idealized conditions of the equations actually exist; similarly we often talk of frictionless planes and elephants whose mass may be ignored in kinematics problems, but there's no implication that these are physically realizable.

 

right. Gotcha.

[Strange]

 

Indeed, but as I understood it from an earlier post, such a world does emerge as a solution to Einstein's field equations. Did I misunderstand?

 

I think "can" rather than "does" might be more apt. There are many possible solutions to the equations, only a subset of which are physically realistic, and only a subset of those which might describe the universe we are in.

Just because it's bugging me - would you like to settle the argument as to whether a second and a light-second are the same thing in General Relativity?

 

A second is a measure of time, a light-second is a measure of distance (the distance light travels in one second - about one and a half million furlongs ).

[swansont]

Just because it's bugging me - would you like to settle the argument as to whether a second and a light-second are the same thing in General Relativity?

 

And if the answer is yes - why ?

 

Thanks!

 

It's not that they are equal, it's that the coordinate used is ct rather than t. c is a constant of proportionality, much like in E=mc² the proportionality constant is c². (thus, mass is a form of energy but you need to multiply by c² to find out how much energy you have)

 

When you do that, you find that there is an invariant length, given by d² = x² + y² + z²- c²t² (aka the spacetime interval, mentioned earlier) All observers agree on this interval.

[Lizzie L]

 

It's not that they are equal, it's that the coordinate used is ct rather than t. c is a constant of proportionality, much like in E=mc² the proportionality constant is c². (thus, mass is a form of energy but you need to multiply by c² to find out how much energy you have)

 

When you do that, you find that there is an invariant length, given by d² = x² + y² + z²- c²t² (aka the spacetime interval, mentioned earlier) All observers agree on this interval.

 

 

OK, that makes sense. Schneibster posted something similar here. Although I still don't get the thing about hurtling through time at the speed of light!

[Dekan]

It's not that they are equal, it's that the coordinate used is ct rather than t. c is a constant of proportionality, much like in E=mc² the proportionality constant is c². (thus, mass is a form of energy but you need to multiply by c² to find out how much energy you have)

 

Reply - I wonder why the proportionality constant is c-squared. That seems to imply a kind of "Flatland"-style 2-D Universe.

Whereas the actual Universe is 3-D. I mean light doesn't travel in a flat 2-D plane. It goes off in all three dimensions,

 

Wouldn't that make a c-cubed constant, more what one would expect?

Edited February 24, 2014 by swansont

[Strange]

 

 

Although I still don't get the thing about hurtling through time at the speed of light!

 

It is a metaphor, you can't take it too literally but one way to think of the effects of relativity (time dilation, length contraction, etc) is that an object moving relative to you swaps some of its "movement through time" for movement through space. The Lorentz transform, which calculates these effects is, effectively, a rotation between the time and space axes.

 

I wonder why the proportionality constant is c-squared.

 

You can think of it as being related to the fact that kinetic energy is given by ¹/₂ m v² (without getting into the whole derivation).

 

Also, velocity³ times mass wouldn't have the units of energy.

Edited February 24, 2014 by Strange

[swansont]

 

Reply - I wonder why the proportionality constant is c-squared. That seems to imply a kind of "Flatland"-style 2-D Universe.

Whereas the actual Universe is 3-D. I mean light doesn't travel in a flat 2-D plane. It goes off in all three dimensions,

 

Wouldn't that make a c-cubed constant, more what one would expect?

 

I think you'll find that (classically speaking) light only goes one direction at a time. As Strange said it's a matter of the units. I suspect you're overthinking the problem.

 

 

OK, that makes sense. Schneibster posted something similar here. Although I still don't get the thing about hurtling through time at the speed of light!

 

That comes (for me, anyway) from looking at the invariant speed, which gives you the ratio of proper time to coordinate time in the ct variable (the ratio being the gamma term that's been described earlier). The length of the vector is always c; one can infer from this that your speed through spacetime is always c. If the object is in motion there is length contraction and time dilation, whose effects cancel in the vector and the objects "speed through time" is slower by gamma. So if your speed through space is not zero, your speed through time has to change to balance things out.

[michel123456]

 

It is a metaphor, you can't take it too literally but one way to think of the effects of relativity (time dilation, length contraction, etc) is that an object moving relative to you swaps some of its "movement through time" for movement through space. The Lorentz transform, which calculates these effects is, effectively, a rotation between the time and space axes.

 

You can think of it as being related to the fact that kinetic energy is given by ¹/₂ m v² (without getting into the whole derivation).

 

Also, velocity³ times mass wouldn't have the units of energy.

Right. Movement through time. It sounds so obvious as you stated. Most people do not accept that fact though.

 

 

 

 

 

------------------

Explaining.

It is also considered as a difference between space & time.

In space, objects change coordinates.

In time, it is often considered that objects do not change coordinates properly: objects are considered to extend from one coordinate to another. people use to say: the moon existed yesterday, it exist today, the moon will exist tomorrow. So, the Moon's existence in time extends from yesterday to tomorrow. As if they were 3 moons (in fact an infinity of moons, each one for any instant of time). And based on this understanding, people create fairy tales on how it would be possible to go back and visit Moon number one in the past.

Which is completely false IMHO.

 

My point is that "movement in time" should be considered exactly as "movement in space". There is no difference. It is a change in coordinates. If the Moon is there today, it means that there is no "other moon" in some "other time" in the past. That "old moon" is gone, it has change coordinates.

 

I hope it is not too difficult to understand and accept.

Edited February 24, 2014 by michel123456

[Lizzie L]

 

I think you'll find that (classically speaking) light only goes one direction at a time. As Strange said it's a matter of the units. I suspect you're overthinking the problem.

 

That comes (for me, anyway) from looking at the invariant speed, which gives you the ratio of proper time to coordinate time in the ct variable (the ratio being the gamma term that's been described earlier). The length of the vector is always c; one can infer from this that your speed through spacetime is always c. If the object is in motion there is length contraction and time dilation, whose effects cancel in the vector and the objects "speed through time" is slower by gamma. So if your speed through space is not zero, your speed through time has to change to balance things out.

 

 

OK. Well, that actually makes sense And to be fair on myself, isn't a million miles (light-seconds?) from what I thought in the first place. Cool. Sanity returns. Thanks.

[studiot]

I thought that discussion on relativity had been declared off topic by hypervalentiodine, since we are supposed to be discussing time and the OP.

 

 

Movement through time. It sounds so obvious as you stated. Most people do not accept that fact though.

 

The OP had the sense to realise that no one can tell you what time is. He was seeking 'a basic understanding'.

 

Now one thing to understand is about the flow of time.

 

Here is some quotes from the recent Cambridge University book 'On Space and Time', edited by Professor Shahn Majid.

 

 

What is the true nature of space and time.........This unique volume brings together world leaders in cosmology, particle physics,quantum gravity, mathematics, philosophy and theology to provide fresh insights into the deep structure of space and time and its wider context............. ....

The one thing that does seem clear is that time flows

 

Lizzie L I suspect you would find much of interest in this book.

Although the book deals also with the possible granularity of space and time, the following is not in the book

 

The issue of time flowing is interesting because of the way we measure it.

 

Does time flow evenly or jerkily?

 

All clocks proceed unevenly, within a tick cycle.

Old fashioned chronometers proceeded with a series of small jerks forwards.

More modern atomic clocks still run at uneven rates through their tick cycle, this can be modelled by SHM.

Edited February 24, 2014 by studiot