Time and space

[Strange]

18 minutes ago, argo said:

i.e..there is only one universal spacetime now. 

No one said that.

18 minutes ago, argo said:

The point is that relativity insists on many points that are now, spacetime on the other hand DOES NOT, it insists on one now.

Space-time is a concept from relativity. There is no single "now" in relativity or space-time. It depends on the observer.

19 minutes ago, argo said:

The evidence for relativity must outweigh the idea of spacetime and no matter how useful spacetime may be it is only a speculation.

As relativity is based on the concept of spacetime, then any evidence for relativity is evidence for the concept of spacetime.

What evidence do you have that relativity and/or spacetime are wrong?

20 minutes ago, argo said:

Spacetime belongs in the trash but instead the whistle blower is.

EVIDENCE?

[Markus Hanke]

47 minutes ago, argo said:

The point is that relativity insists on many points that are now, spacetime on the other hand DOES NOT, it insists on one now.

The evidence for relativity must outweigh the idea of spacetime and no matter how useful spacetime may be it is only a speculation.

This doesn’t make any sense. The theory of relativity is a model of spacetime. The two are not different things. 
And as for simultaneity, it is obvious that this is always a relative concept.

[swansont]

2 hours ago, argo said:

hummm

First

You're saying i cannot define now like the many points that are here and here and here....i.e..there is only one universal spacetime now. 

This overestimates the correct answer by one.

[studiot]

Here is a less than perfect analogy to help you understand the difference between time, space (your thread title) and spacetime.

If I said to you

The object is 5 metres wide and 3 metres high and at a temperature of 20^oC,

Would you be able to calculate its size that is its volume?

Of course not!  The three properties are not conformable into a single unit or whole.

But if I said the object is 5 metres wide and 3 metres high and weighs 1500 kilogrammes, you could, in principle calculate its volume by either knowing or asking for the density.

The density is a constant that can make width, height and mass or weight conformable as it connects dimensions and mass/weight.

This arises because volume x density = mass/weight.

Such a combined approach has certain calculational advantages in the materials handling industry, which is why it is used there.

 

In the same way a constant can connect the linear dimensions of along, across and upwards with time.

This constant is called speed.

This arises because distance = speed x time.

Spacetime is the connection of 1 2 or 3 linear dimensions with time in this way to form a 2, 3 or 4 dimensional unit we call spacetime.

But space and time themselves are always separate entities so if we wish to handle them separately we may do so.

 

However, such a combined approach has certain calculational advantages in the space/satellite industry which is why it is used there.

[argo]

relativity 

21 hours ago, Strange said:

21 hours ago, argo said:

i.e..there is only one universal spacetime now. 

No one said that.

Compartment 1

What do you mean no one said that ? Do you and I exist at the same time, NOW? Spacetime SAYS THAT we do.

Compartment 2

Relativity, which you keep asking me to provide the math and evidence for, says you and I DO NOT exist at the same time, that now is relative.

Please check yourselves, somehow it must seem like you're not, but you're saying two different things. 

 

Edited July 27, 2018 by argo
spelling

[Strange]

8 minutes ago, argo said:

What do you mean no one said that ? Do you and I exist at the same time, NOW? Spacetime SAYS THAT we do

No it doesn't. The concept of "now" (and before or after) depends on the observer.

8 minutes ago, argo said:

Relatively, which you keep asking me to provide the math and evidence for, says you and I DO NOT exist at the same time, that now is relative.

I am not asking you for maths and evidence for relativity but for your own personal theory.

8 minutes ago, argo said:

Please check yourselves, somehow it must seem like you're not, but you're saying two different things. 

You are the one who is claiming that space-time and relativity are different things.

Edited July 27, 2018 by Strange

[argo]

So three dimensions of space and an overlay of the moment now is not your description of spacetime? Pray tell your description then, don't just quote relativity.

[Strange]

48 minutes ago, argo said:

So three dimensions of space and an overlay of the moment now is not your description of spacetime?

No.

48 minutes ago, argo said:

Pray tell your description then, don't just quote relativity.

The only description of space-time that I am familairwith is that from relativity.

Now, where is your EVIDENCE that relativity theory is wrong?

[geordief]

38 minutes ago, Strange said:

No.

The only description of space-time that I am familairwith is that from relativity.

Now, where is your EVIDENCE that relativity theory is wrong?

Does the spacetime model  only apply to classical theories?

 

I mean is there a corresponding model in QM  that could be  (or is?) described as incorporating "spacetime"*?

 

* or something similar....

Edited July 27, 2018 by geordief

[argo]

of course 

26 minutes ago, Strange said:

No.

The only description of space-time that I am familairwith is that from relativity.

Now, where is your EVIDENCE that relativity theory is wrong?

Relativity is not wrong, it says now is relative which is the point- now at different times- means the spacetime model is wrong, it is just a time model. The different times now exists is a time model.

Now where is your description of spacetime.

geordief

the time model apply s to both SR and QM without a single adjustment  

[swansont]

2 hours ago, argo said:

 What do you mean no one said that ? Do you and I exist at the same time, NOW? Spacetime SAYS THAT we do.

That's only possible if you are in the same reference frame. If there is relative motion, you can't define a common now. As the concept us of exceedingly limited use, you might notice that physics uses time tags and Lorentz transforms to discuss when thing happen, rather than a nebulous "now"

[Strange]

1 hour ago, geordief said:

Does the spacetime model  only apply to classical theories?

I mean is there a corresponding model in QM  that could be  (or is?) described as incorporating "spacetime"*?

Quantum field theory incorporates (special) relativity.

[Markus Hanke]

1 hour ago, geordief said:

Does the spacetime model  only apply to classical theories? I mean is there a corresponding model in QM  that could be  (or is?) described as incorporating "spacetime"*?

Both relativistic quantum mechanics, as well as quantum field theory are special relativistic models, i.e. the work on a Minkowski spacetime background. So no, it is not restricted to classical theories. Going even further, String Theory is formulated on a smooth and continuous spacetime background, the geometry of which must be described by the field equations of General Relativity.

[Strange]

1 hour ago, argo said:

Relativity is not wrong, it says now is relative which is the point- now at different times- means the spacetime model is wrong, it is just a time model.

You are still talking nonsense.

"The space-time model" IS relativity. So one cannot be right and the other wrong.

You either need to justify this claim, with mathematics and/or evidence, or you need to admit you are wrong.

Edited July 27, 2018 by Strange

[Markus Hanke]

1 hour ago, argo said:

Relativity is not wrong, it says now is relative which is the point- now at different times- means the spacetime model is wrong, it is just a time model. The different times now exists is a time model.

As already stated earlier, relativity is a model of spacetime. The two are not different things. Special Relativity is just Minkowski spacetime, General Relativity describes any semi-Riemannian manifold (=spacetime) that is a solution to the Einstein equations.

As for the physical interpretation of spacetime itself, it is simply the set of all events, i.e. all points in space at all instances in time. The theory of relativity simply describes how these events are related to one another.

Edited July 27, 2018 by Markus Hanke

[argo]

There is nothing more straight forward than using now but if you want to have a bet each way and keep compartmentalizing then not keeping it simple is key i guess.

Notice when it comes to showing how relativity is more than just now at different times there is a change of tact? 

Sooooo i guess if nobody is going to describe spacetime i will. 

From Wiki

In physics, spacetime is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum.

Relativity of simultaneity says now is relative, that there are many points that are now, but spacetime says there is only one, if you compartmentalize you can switch whenever you like which is exactly what is happening but really you need to choose before i can make any real argument here.

A bet each way

1. one now overlays space

2. one now is relative to every point of space

Awesome how two opposite descriptions can become a single four-dimensional continuum and be totally interchangeable like that.

 

[studiot]

9 minutes ago, argo said:

There is nothing more straight forward than using now but if you want to have a bet each way and keep compartmentalizing then not keeping it simple is key i guess.

Notice when it comes to showing how relativity is more than just now at different times there is a change of tact? 

Sooooo i guess if nobody is going to describe spacetime i will. 

From Wiki

In physics, spacetime is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum.

Relativity of simultaneity says now is relative, that there are many points that are now, but spacetime says there is only one, if you compartmentalize you can switch whenever you like which is exactly what is happening but really you need to choose before i can make any real argument here.

A bet each way

1. one now overlays space

2. one now is relative to every point of space

Awesome how two opposite descriptions can become a single four-dimensional continuum and be totally interchangeable like that.

 

In particular

Quote

Argo

Sooooo i guess if nobody is going to describe spacetime i will. 

 

So did you miss my description 13 posts back ?

[Strange]

23 minutes ago, argo said:

Relativity of simultaneity says now is relative, that there are many points that are now, but spacetime says there is only one

Where does it say that? Stop making stuff up or provide some evidence.

24 minutes ago, argo said:

but really you need to choose before i can make any real argument here.

We choose science. You choose to make stuff up. Where do we go from here?

[geordief]

2 minutes ago, Strange said:

 

(argos' quote "

Relativity of simultaneity says now is relative, that there are many points that are now, but spacetime says there is only one")

 

Where does it say that? Stop making stuff up or provide some evidence.

Is that because there are (in the model) an infinite number of possible Spacetime frames of reference ,each centred on any chosen event ?

 

The task is to "hop" from any one such FOR to any other? 

[Strange]

7 minutes ago, geordief said:

Is that because there are (in the model) an infinite number of possible Spacetime frames of reference ,each centred on any chosen event ?

Not so much centred on different events but, if they are in relative motion, then they will "slice" space-time in different ways. So what one person sees as a distance along a spatial dimension another can see as (partly) a movement along a time dimension (and slightly less movement along the spatial dimension). This is basically because the Lorentz transform between frames of reference is a rotation between the spatial and the time dimension.

[geordief]

5 minutes ago, Strange said:

Not so much centred on different events but, if they are in relative motion, then they will "slice" space-time in different ways. So what one person sees as a distance along a spatial dimension another can see as (partly) a movement along a time dimension (and slightly less movement along the spatial dimension). This is basically because the Lorentz transform between frames of reference is a rotation between the spatial and the time dimension.

So "stationary" vis a vis particular events?(the centre could be anywhere that is stationary wrt that event?)

 

Do all FOR's need to contain  at least one physical event?

[Strange]

Just now, geordief said:

So "stationary" vis a vis particular events?(the centre could be anywhere that is stationary wrt that event?)

Yes. (I think.  )

Just now, geordief said:

Do all FOR's need to contain  at least one physical event?

Events are just the name for the "points" in the 4D coordinates system corresponding to the FoR; I guess they are called "events" because they include time and to distinguish them from (purely spatial) "points". 

 

[geordief]

10 minutes ago, Strange said:

Yes. (I think.  )

Events are just the name for the "points" in the 4D coordinates system corresponding to the FoR; I guess they are called "events" because they include time and to distinguish them from (purely spatial) "points". 

 

Yes I knew that was how "event" was used **. There is no such a concept  as an "empty" event (in that sense)-a point in space time   where nothing actually occurs? Are fields always interacting at every conceivable point in spacetime?

 

**Howard Roark from the com site gave me a thick ear over that

 

 

Edited July 27, 2018 by geordief

[Strange]

Just now, geordief said:

There is no such a concept  as an "empty" event (in that sense)-a point in space time   where nothing actually occurs? Are fields always interacting at every conceivable point in spacetime?

Fields are not part of relativity so there doesn't need to be anything or any activity at an "event".

So, for example, if we consider the Schwarzschild solution to the Einstein Field Equations, then all the events outside the spherical mass are "empty" (a true Schwarzschild black hole only exists in an otherwise empty universe; the use of the solution for real black holes is just a useful approximation).

1 hour ago, argo said:

From Wiki

In physics, spacetime is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum.

This appears to be from this Wikipedia page: https://en.wikipedia.org/wiki/Spacetime 

This does not support your claims at all. In fact, it flat out contradicts your claims. The opening sentence under Definitions says:

Quote

Non-relativistic classical mechanics treats time as a universal quantity of measurement which is uniform throughout space

In other words, it is not relativity, nor unified spacetime, that treats time as something that is the same everywhere. It is pre-relativity theories that did not include space-time.

It then goes on to say:

Quote

In the context of special relativity, time cannot be separated from the three dimensions of space, because the observed rate at which time passes for an object depends on the object's velocity relative to the observer.

In other words, in the model of space-time, time is dependent on the observer who measures it. So there is no "universal now".

No need to apologise, you can just admit you were wrong and we will move on.

 

[argo]

2 hours ago, Strange said:

3 hours ago, argo said:

Relativity of simultaneity says now is relative, that there are many points that are now, but spacetime says there is only one

Where does it say that? Stop making stuff up or provide some evidence.

 

3 hours ago, argo said:

From Wiki

In physics, spacetime is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum.

THE one dimension of time, did you miss this? Take this one dimension of time that you say i made up and add three dimensions of space for spactime to have four dimensions, same dumb argument every time, stop compartmentalizing.

If you're saying now is being fused with every point in space then it is purely a time model of relativity, not a spacetime model with a four dimensional continuum but one point with one dimension at a time.

Apologies for not answering studiot i will later.