Basic understanding of time

[MigL]

Come on Shneibster, even Lorentz ( and Fitzgerald and Poincare ) were familiar with dimensional analysis. That is, when you write down an equation, you check its validity by making sure the units on one side are equivalent to the units on the other. If they are not, your equation isn't worth a d**m.

 

A transform doesn't change units of distance into units of time. It is used to transform an event from one coordinate system to another.

[Lizzie L]

Well, that's a relief!

[Schneibster]

Come on Shneibster, even Lorentz ( and Fitzgerald and Poincare ) were familiar with dimensional analysis. That is, when you write down an equation, you check its validity by making sure the units on one side are equivalent to the units on the other. If they are not, your equation isn't worth a d**m.

 

A transform doesn't change units of distance into units of time. It is used to transform an event from one coordinate system to another.

 

Ummm, sorry, that's exactly what Lorentz says: you can transform space into time and vice versa. Are you, seriously, denying the Lorentz transform? Really?

Well, that's a relief!

 

Not particularly. But I'll put up with it if it's what it takes to teach you.

Edited February 23, 2014 by Schneibster

[Lizzie L]

What is true, of course, is that you can express distance in terms of time by invoking a velocity. Hence light-years and light seconds. But that doesn't turn them into the same units. It does make for neat equations though, because we can declare the speed of light ot be one, and say that moving one light second along a spatial axis is equivalent to moving one second along the time axis, and your cone will make a neat 45%. But the units are still different. A light second is not a second. And I think when you defined the speed of light as one second per second, you meant one light-second per second. Which is obviously true, by definition.

Edited February 23, 2014 by Lizzie L

[hypervalent_iodine]

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Moderator Note

Schneibster, this stops now. If you can't have a discussion without the condescending tone and without insulting the intelligence of others posting here, then please do not post at all. Any more posts of that nature I will be removing and if it keeps up, you will be risking suspension.

[Schneibster]

What is true, of course, is that you can express distance in terms of time by invoking a velocity. Hence light-years and light seconds. But that doesn't turn them into the same units. It does make for neat equations though, because we can declare the speed of light ot be one, and say that moving one light second along a spatial axis is equivalent to moving one second along the time axis, and your cone will make a neat 45%. But the units are still different. A light second is not a second. And I think when you defined the speed of light as one second per second, you meant one light-second per second. Which is obviously true, by definition.

 

Lizzie, the Lorentz transform shows that space and time are all one sort of thing. It also shows that the relation of time to space is a light-second of space is transformed to a second of time. (Not exactly; it's a more complex relation than that. But that space is translated to time, no one argues.) This is the canon of relativity, if there can be such a thing- it's all mathematically provable, which is what Einstein is famous for doing.

[studiot]

 

MigL post#201

A transform doesn't change units of distance into units of time. It is used to transform an event from one coordinate system to another.

 

 

Correct in this case but,

Actually you can transform some derived physical quantities into others with suitable processes, eg the Fourier transform,

 

but see here

 

swansont post#180

Length and space aren't the same thing.

 

 

Edited February 23, 2014 by studiot

[Schneibster]

Note that Fourier transforms are from the frequency domain to the time domain.

 

Just sayin'.

[Lizzie L]

Time domain to frequency domain.

[Schneibster]

Frequency is one over time.

 

And the transforms go both ways.

 

The Fourier transform (English pronunciation: /ˈfɔərieɪ/), named after Joseph Fourier, is a mathematical transformation employed to transform signals between time (or spatial) domain and frequency domain, which has many applications in physics and engineering. It is reversible, being able to transform from either domain to the other. The term itself refers to both the transform operation and to the function it produces.

 

Wikipedia: http://en.wikipedia.org/wiki/Fourier_transform

 

And you really should have known better than that, Lizzie. You actually do, I know for a fact; you have to. You can't do your job otherwise.

Edited February 24, 2014 by Schneibster

[Lizzie L]

Yes, for some functions you can use the inverse Fourier transform to get your time series back.

 

But this is a bit off topic.

 

The Lorentz operation transforms your data into a different reference frame. It doesn't transform the axes into different units. At least not as far as I can see, and at least some people seem to agree.

[Schneibster]

Lizzie, that's not hard math either, and it's reversible like almost all of physics.

 

You were the one who brought it into the topic, and you got pwnt. It's time you admit it and start learning some real physics instead of constantly playing games and trying little digs about how Galilean physics works when you don't understand SR.

 

A transform is a transform. A transform cannot make different things the same; that's not what transforms do. Your refusal to admit that this means that space and time are "essentially the same thing" is without reasonable evidence. You are denying relativity.

[studiot]

So getting back to the Lorentz tranformation,

 

You have stated (correctly) that v is velocity, but have not stated what is travelling at this velocity or what frame it is being measured in.

 

Without this information the formulae given cannot be used.

[Schneibster]

Actually, the hyperbolic trig formulae work fine.

 

They merely require you to abandon your ridiculous prejudice in favor of "velocity" and use real relativistic rapidity instead and start doing real physics with 4d rotations like Lorentz and Minkowski and Einstein told us we were supposed to.

Edited February 24, 2014 by Schneibster

[studiot]

 

Schneibster post #156

 

t → (cosh s)t + (sinh s)x

x → (sinh s)t + (cosh s)x

y → y

z → z

 

Or, if you prefer,

 

t → √(1 - (v²/c²)) * (t - vx)/c²

x → √(1 - (v²/c²)) * (x - vt)

y → y

z → z

 

Well it was clearly you who introduced them.

 

In two out of eight equations you have used the symbol v, which you tell me stands for velocity.

 

Why is it so unreasonable to ask what is travelling at this velocity and in what coordinate system?

Edited February 24, 2014 by studiot

[Schneibster]

Wow. I "introduced" them. So do you think I invented relativity? Is this supposed to be some sort of unscientific thing I just came up with out of my bowels? Are you seriously questioning relativity or the Lorentz transform? If you are, on what grounds, please?

 

 

Well it was clearly you who introduced them.

 

In two out of eight equations you have used the symbol v, which you tell me stands for velocity.

 

Why is it so unreasonable to ask what is travelling at this velocity and in what coordinate system?

 

How about if you stick with the hyperbolic trig versions? Are they too difficult for you to understand?

Edited February 24, 2014 by Schneibster

[Lizzie L]

Lizzie, that's not hard math either, and it's reversible like almost all of physics.

 

You were the one who brought it into the topic, and you got pwnt.

 

Oh, give over, Schneibster. You were the one who said "Note that Fourier transforms are from the frequency domain to the time domain". I just pointed out that they go the other way. It's true that the inverse function will often take you back (although not in practice in my field). Neither of us were "pwnt".

 

It's time you admit it and start learning some real physics instead of constantly playing games and trying little digs about how Galilean physics works when you don't understand SR.

 

 

I'm neither playing games nor "trying little digs". I was just trying to show you that "x-vt" doesn't give convert the x dimension into t!

 

 

A transform is a transform. A transform cannot make different things the same; that's not what transforms do.

 

 

Well, it depends entirely on what you are talking about. But when the transform is from one reference frame into another it doesn't change the units. Which was my point. So it's good if you agree.

 

 

Your refusal to admit that this means that space and time are "essentially the same thing" is without reasonable evidence. You are denying relativity.

 

Well, no, I'm not. I don't think that "space and time" are "essentially the same thing". I think they are dimensions of the same thing ("spacetime"), but I think they are in different units. And I don't think that is "denying relativity".

 

But clearly you think I've got that wrong. That's fine. Let's leave it there.

[studiot]

If you are going to introduce equations then you should be prepared to answer legitimate questions about them.

 

I am sorry you appear to feel vindictive about this. Surely it is easier to simply state what you think is travelling at a velocity you have granted it.

 

And no, I do not think you invented relativity, nor was I discussing it.

 

The discovery of the Lorenz transformation preceeded Einstinian relativity and was a practical observation that is actually independent of it.

[Schneibster]

 

Oh, give over, Schneibster. You were the one who said "Note that Fourier transforms are from the frequency domain to the time domain". I just pointed out that they go the other way. It's true that the inverse function will often take you back (although not in practice in my field). Neither of us were "pwnt".

 

In fact you denied it was two way.

If you are going to introduce equations then you should be prepared to answer legitimate questions about them.

 

 

 

I did. I became annoyed when you started questioning their postulates. No mathematician does that without acknowledging that's what they're doing. But you did.

 

Then you made claims about "correctness" and have not yet withdrawn them, when it's been shown that a prominent relativist says you're wrong.

Lizzie, if you want to talk about relativity, learn its postulates first. That is my best polite advice. You do not know them and it is painfully obvious.

 

Studiot, likewise, but far more. You simply do not understand spacetime physics if you do not understand relativity, and I'm sorry but you do not understand relativity.

 

Saying "I included time, see, t = t" is risible. Please don't repeat this kind of stuff.

Edited February 24, 2014 by Schneibster

[hypervalent_iodine]

!

Moderator Note

Please stop with the bickering.

 

This has also gone a little off topic. I suggest that members refresh themselves with what this thread was about by re-reading the OP.

[Lizzie L]

Absolutely (ETA and apologies!) The OP said:

 

I think time is the movement of things. I am not an expert in physics so by 'things' I mean any fundamental particles. On neutron stars, the gravity is very high. This strong gravity pulls things down, so things move slowly than, say, on the Earth. Thus, time on neutron stars becomes slow. Time on an Earth-orbiting space station goes a little bit faster, because the gravity is a little bit lower than on the surface of the Earth.

Time before the Big Bang did not exist, because there were no things before the Big Bang. When there are no things, there is no way to measure the passage of time. Nobody is there, and of course no clock is there. This is indistinguishable from time being stopped.

Theoretically I could stop time, if I could stop the movements of everything (all particles). If everything stops, this is indistinguishable from time being stopped.

 

 

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.

 

Until someone can persuade me that there is a spacetime that is unit free I'm sticking to my guns here

 

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.

Edited February 24, 2014 by Lizzie L

[Schneibster]

Neither Strange nor I has made any discernible difference and I see no further point.

[mooeypoo]

Well, if we are going to measure time in seconds, that's fine by me, and by using the speed of light we can readily get a distance measure from that e.g. light-seconds (we don't need metres as well).

 

But in that case I rest my case: time is measured in terms of change - if you don't have a changing thing, you can't measure time. And if you can't measure time, you don't have a way of putting anything on a t axis.

 

QED

 

*harrumph*

I agree up to the part where you state time is measured in terms of change. That doesn't answer 2 points: 1, swansont's point about a stable atom that can spontaneously decay (i'll have to find the post # for more accurate point) and 2, the fact time is relative to other perspectives, and seems to slow down the faster you go (so it is affected by speed, which is change, but not necessarily is defined by it)

 

I understand the problem of the definition -- I think the problem is a lot deeper than we may realize or that mathematics technically represents, but I am not sure I am comfortable settling on your definition of time. It sounds to me to be as arbitrarily convenient as the one that states time is this "property" of space.

 

I'm not sure it fits all cases we discussed.

[Schneibster]

Absolutely (ETA and apologies!) 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.

 

Lizzie, time is a dimension, and as Strange, I, and many others have tried to tell you it is essentially the same as space. The postulates that say so have been the basis of the most successful theory of physics in the history of the human race for a hundred years.

 

I really don't know what else to say.

[Lizzie L]

I agree up to the part where you state time is measured in terms of change. That doesn't answer 2 points: 1, swansont's point about a stable atom that can spontaneously decay (i'll have to find the post # for more accurate point) and 2, the fact time is relative to other perspectives, and seems to slow down the faster you go (so it is affected by speed, which is change, but not necessarily is defined by it)

 

I understand the problem of the definition -- I think the problem is a lot deeper than we may realize or that mathematics technically represents, but I am not sure I am comfortable settling on your definition of time. It sounds to me to be as arbitrarily convenient as the one that states time is this "property" of space.

 

I'm not sure it fits all cases we discussed.

 

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

 

Lizzie, time is a dimension, and as Strange, I, and many others have tried to tell you it is essentially the same as space. The postulates that say so have been the basis of the most successful theory of physics in the history of the human race for a hundred years.

 

I really don't know what else to say.

 

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.