Questions about Space, Time, Motion, Blackholes and Stuff

Discussions on the nature of being, existence, reality and knowledge. What is? How do we know?

Questions about Space, Time, Motion, Blackholes and Stuff

Postby rajnz00 on April 12th, 2017, 4:58 am 

I thought about it. If you want to find out about something you don’t know, you have to tackle it like a murder mystery, a who-dun-it. Except in this case it’s a “what-dun-it” and “how-dun-it” and “why-is-it” and “what is it”.

The body is the Universe around us, the evidence is in our experiments, our telescopes, atom smashers. Our detectives are our scientists and thinkers. So here goes:

First Space

Space – Well the best theory we have is General Relativity Rμv - 1/2 Rgμv= 8πG/c4 Tμv
space curves where there is matter. That is it. The equation fits into half a line, and there is nothing more. A vision – that space curves – became an equation. But within this equation there is a teeming universe.” Carlo Rovelli

Great Carlo – but what the hell is it? What is it made of? Remember Newton? He’s the guy who gave us classical mechanics and the theory of gravity. This is what he said “That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking, can ever fall into it.” He confessed he did not know and left it to future generations to find out.

So Einstein comes along and says – no, no there is no force, its just space bending. When you plonk the Sun in it, space bends, so the planets are just rolling down the natural curvature. But it seems to me Einstein, though your equations maybe more accurate, that there must be something that bends and without telling us what it is, that explanation is just as great an absurdity. Is it frictionless? What is it made of?

Paul Dirac had a stab at answering the question. The universe is chock a block full of negative electrons, with infinite negative energy. We are not aware of it just like fish aren’t aware of the water around it. Every now and then a cosmic Gamma ray displaces one of these electrons to produce a positron, which is an anti-matter particle, or a bubble with a +ve charge, which annihilates when meeting an electron.

May not be so, but it’s one answer. That's about as much as I will do for now. Any other answers?
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby mitchellmckain on April 12th, 2017, 12:30 pm 

A question about what space is made of would not even occurred to scientists before Einstein when it was presumed to be this fixed absolute structure of Euclid which was the mental backdrop of all thoughts regarding basic geometry. It was only Einstein and General Relativity which made space itself a product of scientific equations and thus something which changed and evolved. This led contrary to Einstein's own expectations to the conclusion that space-time came into being at some point in the past along with the universe.

But things haven't changed completely because we never think of space-time as a thing which is composed of something but rather the geometrical structure of something else. If I put before you an object, say a book, and ask you to tell me of its length, height, and thickness, how would you respond if I then asked what its length was made of apart from the book itself? Does that make any sense? It is the book which is composed of materials and it has dimensions by means of design in its construction. But it makes no sense to say that the length, height, and thickness has any composition apart from this.

Thus it is likewise natural to think of the space-time of the universe in the same say, to say that its dimensions are also the geometrical structure of the universe itself and we even have the means in Einstein's Field Equation to explain how that happens. It is according to the equation that the dimensions of the universe (assuming it is even finite) alters as a function of its composition. It is true that we have speculated there may be some negative energy associated with this which somehow makes the total energy of the universe a zero sum. But that doesn't necessarily imply that space-time is made of negative energy stuff. This is easily interpreted as simply an energy requirement and thus to say space-time is a product of its positive energy content.
User avatar
mitchellmckain
Member
 
Posts: 387
Joined: 27 Oct 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 12th, 2017, 1:07 pm 

Einstein and General Relativity which made space itself a product of scientific equations and thus something which changed and evolved.

One thing we know about this "body" - the Universe - that people are trying to figure out, our most spectacularly successful theories, General Relativity and Quantum Mechanics, are both wrong. They disagree with each other and are incompatible. GR breaks down at the "singularity", quantum mechanics fails with gravity. In a court of law, they would produce a not guilty verdict, or the null hypotheses fail to be disproved.

The Ptolemaic model, was also spectacularly successful and Newtons equations are used till this day, but they are both wrong.

I just briefly touched on Dirac's hypothesis. It was in response to a problem. At the time he proposed that electrons which completely fill the Universe, when knocked out, formed holes or bubbles these were Protons, because Positrons were not known known then and they annihilate when they come together. He realised the problem with the differences of mass, protons being 1836 times more massive. But since then positrons have been discovered and they do annihilate with electrons.

As for energy, he said the Universe was chocker with electrons, every conceivable, allowable space, like with the atom was occupied with them and thus space had infinite negative energy. This was quite different to the current explanation that the Universe has Zero energy because the negative energy of gravity cancels out the positive energy of matter.
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 12th, 2017, 1:11 pm 

And coming back to Dirac's theory, it satisfies in one respect. What bends? Something must bend. What is so rigid that when a star is placed in it it affects another body thousands of millions of kilometres away?
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 13th, 2017, 1:42 am 

Time, Motion, Simultaneity

Time – the passage of time – the apparent unidirectional flow of time.

Einstein – (paraphrasing) - “that disagrees with my equations, so it’s an illusion”. Einstein, what a cop out, or how deluded can you get? It damn well flows.

With apologies to Fitzgerald and Omar Khayyam -

One thing I know that time flies,
One thing is true, the rest is lies
A rose that once has bloomed,
Forever dies

Einstein was an intelligent guy, but he was a bit of a con-man. He fraudulently got fame from a theory that was probably made by his then wife, who he treated very badly. E=mc^2 was attached, apropos nothing, as a much later afterthought, to his paper. An equation that was floating around long before he usurped it. He would attach his name onto theories and equations proposed by others, which he had nothing to do with, and probably barely understood. Anyway, that’s another story.

I kick a ball in my backyard, someone does so in London, another on a planet around Alpha Centauri and another in the Andromeda galaxy. Can we ever say they were simultaneous?

One thing I can say with certainty about my foot kicking the ball and the ball getting kicked, that contact was simultaneous. We were both there in the same place at the same time. The other thing I can say with certainty, once kicked it remains kicked. I cannot undo that event. And I’m pretty sure no one else can, anywhere in the Universe.

There has to be some Universal time. Some time like GMT on Earth that we can apply to the Whole Universe.

Wikipedia – “distant simultaneity – whether two spatially separated events occur at the same time – is not absolute, but depends on the observer's reference frame.”

“a car crash in London and another in New York, which appear to happen at the same time to an observer on the earth, will appear to have occurred at slightly different times to an observer on an airplane flying between London and New York. The question of whether the events are simultaneous is relative [Why? The discrepancy is only apparent.]: in the stationary earth reference frame the two accidents may happen at the same time but in other frames (in a different state of motion relative to the events) the crash in London may occur first, and in still other frames the New York crash may occur first. “

However, ifthe time between event A and event B is greater than the distance between them divided by the speed of light, the order is preserved … "event A precedes event B" in all frames of reference.””

What??!! Don’t we have a formula for absolute simultaneity here? What if the Time between event A and event B is exactly equal to the distance between them divided by the speed of light? Wouldn’t they be simultaneous?

But what “Time between event A and event B” is he talking about? How do we measure it? Unless we have a Universal time?

Comments?
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby mitchellmckain on April 13th, 2017, 2:45 am 

rajnz00 » April 12th, 2017, 12:07 pm wrote:
Einstein and General Relativity which made space itself a product of scientific equations and thus something which changed and evolved.

One thing we know about this "body" - the Universe - that people are trying to figure out, our most spectacularly successful theories, General Relativity and Quantum Mechanics, are both wrong. They disagree with each other and are incompatible. GR breaks down at the "singularity", quantum mechanics fails with gravity. In a court of law, they would produce a not guilty verdict, or the null hypotheses fail to be disproved.

Incorrect. They are not wrong. They spectacularly right. They do not contradict each other. The most we can say is that neither are complete descriptions of the universe by themselves. But then why should they be? There is no guarantee that a complete description of the universe can exist in a single mathematical theory. We cannot even say they are incompatible since both have been integrated into M-theory, either as a quantum theory of branes or as an 11-dimensional supergravity (this is an extension of Kaluza-Klein in which electromagnetism is included in a 5 dimensional version of General Relativity). Sure this M-theory is not completely worked out and we do not have proof it is correct, but it still shows that the two theories are not incompatible.

rajnz00 » April 12th, 2017, 12:07 pm wrote:The Ptolemaic model, was also spectacularly successful and Newtons equations are used till this day, but they are both wrong.

Also incorrect. The Ptolemaic model is a correct description of the motion of stars and planets in the sky of Earth. Newton's equations continue to be taught in high schools because they are correct. Again your attempt to equate some inability to describe and calculate absolutely everything with being incorrect is absurd. And the fact is that the failure of Bell's inequality shows this can never happen anyway.

rajnz00 » April 12th, 2017, 12:07 pm wrote:I just briefly touched on Dirac's hypothesis. It was in response to a problem. At the time he proposed that electrons which completely fill the Universe, when knocked out, formed holes or bubbles these were Protons, because Positrons were not known known then and they annihilate when they come together. He realised the problem with the differences of mass, protons being 1836 times more massive. But since then positrons have been discovered and they do annihilate with electrons.

I am well familiar with this hypothesis and also with the fact that it has long been replaced. But it was never believed to be a description of the universe. What so many fail to understand is that it is a standard technique of physics to look at things from different perspectives as tools to help with calculation. Thus we have no problem with looking at a light being both particles and waves at the same time. It does not mean that either view is wrong. Like everything else in physics, both are right to the degree in which they help calculate the results of experiments.
User avatar
mitchellmckain
Member
 
Posts: 387
Joined: 27 Oct 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby BurtJordaan on April 13th, 2017, 3:14 am 

rajnz00 » 13 Apr 2017, 07:42 wrote:“However, if … the time between event A and event B is greater than the distance between them divided by the speed of light, the order is preserved … "event A precedes event B" in all frames of reference.””

What??!! Don’t we have a formula for absolute simultaneity here? What if the Time between event A and event B is exactly equal to the distance between them divided by the speed of light? Wouldn’t they be simultaneous?

But what “Time between event A and event B” is he talking about? How do we measure it? Unless we have a Universal time?

Raj, the whole point of relativity theory is that due to the equivalence of all inertial frames, or better stated, that the laws of physics are the same in all inertial frames, there cannot exist an "absolute simultaneity". Simultaneity depends on the inertial frame chosen for the measurement and each relatively moving frame has a different notion of what is simultaneous. The principle has been experimentally demonstrated many times in the past century.

When "the Time between event A and event B is exactly equal to the distance between them divided by the speed of light", they are said to be separated by a light-like interval in all inertial frames. They are not simultaneous in any inertial frame, because you cannot have an inertial frame where the event lies on the plane of any spatial axis (x,y,z). Why not? Because then light would have to be static/stationary in that inertial frame, which is demonstrably impossible.

Time and distance are always stated relative to some inertial frame. If the time interval dT between two events is larger that than the space interval dX, it is a time-like interval in every inertial frame that exists. Likewise for the reverse, i.e. space-like intervals. Hence, temporal ordering of cause and effect events are maintained absolutely.

I'm not one for discussing Epistemological implications, but the science is very clear about it. If you have more issues with the science, please ask.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2256
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby mitchellmckain on April 13th, 2017, 3:54 am 

BurtJordaan » April 13th, 2017, 2:14 am wrote:When "the Time between event A and event B is exactly equal to the distance between them divided by the speed of light", they are said to be separated by a light-like interval in all inertial frames. They are not simultaneous in any inertial frame, because you cannot have an inertial frame where the event lies on the plane of any spatial axis (x,y,z). Why not? Because then light would have to be static/stationary in that inertial frame, which is demonstrably impossible.

Time and distance are always stated relative to some inertial frame. If the time interval dT between two events is larger that than the space interval dX, it is a time-like interval in every inertial frame that exists. Likewise for the reverse, i.e. space-like intervals. Hence, temporal ordering of cause and effect events are maintained absolutely.


As a tiny nitpicking correction and rephrasing...

With a null interval or what BurtJordan is calling "light-like," you can get as arbitrarily close to being simultaneous by choosing the right inertial frame. For space-like intervals there is an inertial frame in which they are simultaneous (the basis of the dubious and relative idea simultaneous elsewhere), and for time-like intervals there is no such inertial frame (never simultaneous). But yes the main point is that this principle of local causality makes a clear separation between past and future locally in these two cones which are the same in all inertial frames.
User avatar
mitchellmckain
Member
 
Posts: 387
Joined: 27 Oct 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby BurtJordaan on April 13th, 2017, 4:00 am 

Agreed. ;)
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2256
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 13th, 2017, 6:40 am 

Hi Burt, thanks for the clarification re: simultaneity. I have some questions. You wrote:
When "the Time between event A and event B is exactly equal to the distance between them divided by the speed of light", they are said to be separated by a light-like interval in all inertial frames. They are not simultaneous in any inertial frame, because you cannot have an inertial frame where the event lies on the plane of any spatial axis (x,y,z). Why not? Because then light would have to be static/stationary in that inertial frame, which is demonstrably impossible.

mitchellmckain on the other hand said
With a null interval or what BurtJordan is calling "light-like," you can get as arbitrarily close to being simultaneous by choosing the right inertial frame.
with which you agreed.

My question then is, if for these "Null events" or "light-like events", whatever you decide to call them, why is it that we can get as "arbitrarily close" to making them simultaneous, by choosing an appropriate inertial frame but not actually reach simultaneity?
And my previous question was - How to do we measure exactly the times of the events at A and B, to be able to perform those calculations?

Regards

Raj
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 13th, 2017, 6:45 am 

mitchellmckain, in your reply to me, the politest thing I can say is that you are wrong on every count.
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby BurtJordaan on April 13th, 2017, 8:19 am 

rajnz00 » 13 Apr 2017, 12:40 wrote:My question then is, if for these "Null events" or "light-like events", whatever you decide to call them, why is it that we can get as "arbitrarily close" to making them simultaneous, by choosing an appropriate inertial frame but not actually reach simultaneity?

Because two inertial frames can theoretically have a relative speed that is arbitrary close to c, but never quite c. In such frames, the time interval between the two events will always be greater than zero.

And my previous question was - How to do we measure exactly the times of the events at A and B, to be able to perform those calculations?

You set up a grid of synchronized clocks for each inertial frame and the clocks co-located with the two events for each frame simply record the time of each event and subtract them to get delta_t. If the two events are light-like separated, each will frame will get a non-zero result. At the same time, the distance between the two relevant clocks will also equal c delta_t for each frame, showing that the events are indeed separated by a light-like interval for each of them.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2256
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 13th, 2017, 2:24 pm 

Hi Burt,
Many thanks for your reply.
I'm not quite sure I understand how we could set up a grid of synchronized clocks for each inertial frame, but let us assume we can and do, this is what is puzzling me:
Let
Time of event A = Ta
Time of event B = Tb
Distance between A and B = d
If (Ta – Tb) > d/c
Then Event A occurs before event B in All inertial frames.
I presume also
If Tb – Ta > d / c Then event B occurs before event A in All inertial frames
But if Ta – Tb = d/c then A and B are not simultaneous in Any inertial frame

If we plug in some real numbers here
Assume:
c = 3 x 105 Km.sec-1
Let d = 3 x 106 Km
Therefore d/c = 10 sec
If Ta – Tb = 11 sec, Then A occurs before B
If Ta – Tb = 9 sec then does B occur before A?

And if Ta – Tb = 10 sec then events A and B are not simultaneous in any inertial frame?
This is puzzling to me
Regards
Raj
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby BurtJordaan on April 13th, 2017, 4:22 pm 

rajnz00 » 13 Apr 2017, 20:24 wrote:Let d = 3 x 106 Km
Therefore d/c = 10 sec
If Ta – Tb = 11 sec, Then A occurs before B
If Ta – Tb = 9 sec then does B occur before A?

And if Ta – Tb = 10 sec then events A and B are not simultaneous in any inertial frame?


Nope. In all your cases, B happens before A, so that Tb is smaller than Ta.

In a (x,cT) spacetime diagram, let A be at (xa=0, cTa=11) and B at (xb=10, cTa=1), so that there is a lightlike interval (Ta-Tb=0) between them. The two events are obviously not simultaneous. It is a 45 degree downwards slope line, where simultaneous would be a horizontal line.

Now think what would happen if you just change cTa to 12. Not much, except that the interval is now timelike, with a steeper slope. For cTa changed to 9, the interval is now spacelike, with a shallower slope, but in all cases B happens clearly before A.

Try drawing the diagram - it speaks a thousand words!
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2256
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 13th, 2017, 6:39 pm 

Hi Burt,
Yes, you are right of course. B would occur before A, if Tb is smaller than Ta. And thanks also for clearing up the confusion in my mind. Simultaneous events would occur only along the horizontal lines, and only for that inertial frame. PS it looks to me that Wikipedia has worded it unclearly, to imply A would occur before B. But no matter, now that is out of the way onto more weighty matters :)
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby mitchellmckain on April 13th, 2017, 8:00 pm 

BurtJordaan » April 13th, 2017, 3:22 pm wrote:
rajnz00 » 13 Apr 2017, 20:24 wrote:Let d = 3 x 106 Km
Therefore d/c = 10 sec
If Ta – Tb = 11 sec, Then A occurs before B
If Ta – Tb = 9 sec then does B occur before A?

And if Ta – Tb = 10 sec then events A and B are not simultaneous in any inertial frame?


Nope. In all your cases, B happens before A, so that Tb is smaller than Ta.

In a (x,cT) spacetime diagram, let A be at (xa=0, cTa=11) and B at (xb=10, cTa=1), so that there is a lightlike interval (Ta-Tb=0) between them. The two events are obviously not simultaneous. It is a 45 degree downwards slope line, where simultaneous would be a horizontal line.

Now think what would happen if you just change cTa to 12. Not much, except that the interval is now timelike, with a steeper slope. For cTa changed to 9, the interval is now spacelike, with a shallower slope, but in all cases B happens clearly before A.


Except...

While in the first two cases the order of events is independent of inertial frame, the case of cTa = 9 ls (spacelike) means the order of events depends on the inertial frame. The interval (squared) ds2 = dx2 - (c dt)2 remains the same in all inertial frames, but when this is positive (space-like), this means that under a change of inertial frame the time interval dt can pass through zero (simultaneous) to the opposite sign (with a corresponding change in dx to keep the interval constant) and thus the events can be reversed in order. When the interval is negative (time-like) then this cannot happen. For the null interval, dt goes to zero only in the limit as the speed goes to c, but that limit is not an inertial frame. Objects with mass cannot go the speed of light, and it would take infinite energy if they could.
User avatar
mitchellmckain
Member
 
Posts: 387
Joined: 27 Oct 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 13th, 2017, 8:34 pm 

I don't get what you are saying.
Are you saying
1. That when the time interval is greater than 10 sec the order of events are independent of the frame?
2. When the time interval goes from 11 sec to 9 sec, the order of events reverse?
3. They pass through simultaneous while doing so?
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 14th, 2017, 1:34 am 

Ok I felt I needed to figure this out for myself, so I have. This is interesting stuff but I need to move on. Some the interesting things I learned:
(In simple language, without any mumbo-jumbo)
The interval between two events are light-like, if they are (can be) connected by a signal of light.
Pairs of events which are not connected (and cannot be connected) by any signal at all, are called "space-like" events.
The proper time is the time measured by a freely moving observer, carrying a watch with him.
Proper time is an invarient - every observer in every inertial frame will measure the same proper time between the two events.
It is defined by:
Δτ2 = c2Δt2 − Δx2 − Δy2 − Δz2
Δτ2 is positive if you can travel between the two events without travelling faster than light

There are some beautiful explanations here: https://physics.stackexchange.com/quest ... rval/77160 , by John Rennie and user12262

I like to make complicated things simple, that's probably why people listen, even when I post on other's posts like Dave's. Some people flaunt their credentials and feel it gives them authority to spout a whole lot of nonsense about everything under the sun, such as Ptolemy's model and Newtons Gravity being correct.
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby BurtJordaan on April 14th, 2017, 2:29 am 

Raj, I'm glad you've got it.

Take note that Mitchell is right about the apparent order of spacelike events that can reverse between inertial frames. The real issue is that since spacelike separated events (like dx=10, dcT=9 in your example) are not causally connected, in the sense that neither one can be the cause of the other one - because not even light can travel between them.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2256
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby mitchellmckain on April 14th, 2017, 3:06 am 

rajnz00 » April 14th, 2017, 12:34 am wrote:Ok I felt I needed to figure this out for myself, so I have. This is interesting stuff but I need to move on. Some the interesting things I learned:
(In simple language, without any mumbo-jumbo)
The interval between two events are light-like, if they are (can be) connected by a signal of light.
Pairs of events which are not connected (and cannot be connected) by any signal at all, are called "space-like" events.
The proper time is the time measured by a freely moving observer, carrying a watch with him.
Proper time is an invarient - every observer in every inertial frame will measure the same proper time between the two events.
It is defined by:
Δτ2 = c2Δt2 − Δx2 − Δy2 − Δz2

Close... for proper time you want the units of time so...
Δτ2 = Δt2 − (Δx2 − Δy2 − Δz2)/c2
in other words the proper time closely related to the interval s ...
Δτ2 = - Δs2 / c2

rajnz00 » April 14th, 2017, 12:34 am wrote:Δτ2 is positive if you can travel between the two events without travelling faster than light

which means they can be causally connected.

rajnz00 » April 14th, 2017, 12:34 am wrote:I like to make complicated things simple, that's probably why people listen, even when I post on other's posts like Dave's. Some people flaunt their credentials and feel it gives them authority to spout a whole lot of nonsense about everything under the sun, such as Ptolemy's model and Newtons Gravity being correct.

And some people like to delude themselves that what is being taught in school is all wrong. Gives them all sorts of stupid excuses.
User avatar
mitchellmckain
Member
 
Posts: 387
Joined: 27 Oct 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 14th, 2017, 1:15 pm 

Burt: “Take note that Mitchell is right about the apparent order of spacelike events that can reverse between inertial frames.”
Yes I figured that out on my own. (So I was not wrong in asking that question). The maths is not complicated, only the jargon is unfamiliar to me, (“spacelike” and “timelike”, and what precisely you meant by dx and dcT)
Burt: “The real issue is that since spacelike separated events (like dx=10, dcT=9 in your example) are not causally connected, in the sense that neither one can be the cause of the other one”
Even “timelike” separated events need not be causally connected, but it does make one think about causality. The question that springs to my mind is, if events that are “spacelike” (my definition of “spacelike” events would be - events closer together in time, than the time taken for light to travel the distance between them, or, mathematically, where dcT < dx, using your jargon) cannot be causally connected, then why did Einstein believe in causality? Or why is it said that GR is causal, like Newton’s mechanics?
Burt: “because not even light can travel between them.”
I would make the language clearer for people who can understand maths and English, but are unfamiliar with the terms of relativity. Light can certainly travel between the location of the events, in my example, which are a mere 3 million kilometres apart, just the events are closer together in time, than the time it would take for light to travel between them.

mitchellmckain: Δτ2 = Δt2 − (Δx2− Δy2 − Δz2)/c2
Right
mitchellmckain: in other words the proper time closely related to the interval s ...
Δτ2 = - Δs2 / c2
What is "the interval s" or Δs?

"some people like to delude themselves" True. One should not confuse book knowledge with intelligence, which is more closely related to reasoning and figuring out.
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby BurtJordaan on April 14th, 2017, 2:59 pm 

rajnz00 » 14 Apr 2017, 19:15 wrote:The maths is not complicated, only the jargon is unfamiliar to me, (“spacelike” and “timelike”, and what precisely you meant by dx and dcT)

It will always be a problem when you read relativity, but fortunately the definitions are easily found on the web. It is somewhat expected that if you ask advanced questions (like your the topic title suggests), you know most of the relativistic terms.

... then why did Einstein believe in causality? Or why is it said that GR is causal, like Newton’s mechanics?

They are equivalent in terms of causality, except that Newton had one absolute simultaneity for all inertial frames and Einstein gave us relative (reference frame dependent) simultaneity. Experiments favor Einstein's definition.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2256
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 14th, 2017, 7:21 pm 

BurtJordaan wrote: It is somewhat expected that if you ask advanced questions (like your the topic title suggests), you know most of the relativistic terms.

There are many levels for discussion. I started this topic, for people like me, who are not Nuclear scientists or Theoretical Physicists, but yet interested in the world around us. Even Stephen Hawking’s Brief history of Time doesn’t contain too much technical jargon. We can discuss and learn along the way. I think its much more fun that way.
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby BurtJordaan on April 15th, 2017, 1:05 am 

That's fine, learn as we go, but expect to be referred to Wikipedia often. It will be a bit cumbersome if respondents have to define the relevant terminology for every new discussion.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2256
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby mitchellmckain on April 15th, 2017, 3:16 am 

mitchellmckain » April 14th, 2017, 2:06 am wrote:
Close... for proper time you want the units of time so...
Δτ2 = Δt2 − (Δx2 − Δy2 − Δz2)/c2


Oops.. you guys missed a chance to correct me there. typo...

The correct formula is...

Δτ2 = Δt2 − (Δx2 + Δy2 + Δz2)/c2



Books are just one of the mediums of human communication by which we pass what we learn on to the next generation. The "book larnin" which mouth breathers of the past looked down on were probably thinking of the more complicated/abstract stuff of math, science, technology, and such which is too hard to pass on by means of word of mouth alone. The middle ages might seem like a fine and dandy time to you, but I see only squalor and ignorance. As for confusing education with intelligence... LOL I don't bother measuring such thing. What is the point? Seems to me, it is more important what you do with your abilities than any fact that you have them. But... how can you contribute anything of significance if you don't even know what has been done?
User avatar
mitchellmckain
Member
 
Posts: 387
Joined: 27 Oct 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 15th, 2017, 10:02 am 

Mitchellmckain, I should have caught that obvious, elementary school mistake, made by you, but then it would have been a shame to deprive you the pleasure of correcting your own mistake and making that remark. Getting concepts right are more important than making mistakes. I’m sure it would have given you far greater pleasure catching any mistake I made in the concepts I enunciated in that post.

Correcting your elementary algebra mistake is appreciated, but could you shed light on why Einstein believed in causality and GR is said to be causal, when so much of the Universe events cannot possibly be causal according to SR and GR?
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 15th, 2017, 10:36 am 

But since you do want me to correct your maths, and we are talking about proper time, then proper time Δτ, is equal to

Δτ = [Δt2 − (Δx2 + Δy2 + Δz2)/c2]1/2
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby mitchellmckain on April 15th, 2017, 5:21 pm 

rajnz00 » April 15th, 2017, 9:02 am wrote:Mitchellmckain, I should have caught that obvious, elementary school mistake, made by you, but then it would have been a shame to deprive you the pleasure of correcting your own mistake and making that remark. Getting concepts right are more important than making mistakes. I’m sure it would have given you far greater pleasure catching any mistake I made in the concepts I enunciated in that post.

It is not about pleasure. This is how real science works. Not only is getting good at this stuff about learning to catch your mistakes faster but about everyone involved correcting each other in order to get it right -- and especially NOT getting uptight about it! For those who actually do it rather than merely talking about it, science and physics in particular is NOT about getting concepts right but about getting the right answer -- and that is even MORE true when your are doing research rather than taking a class.

rajnz00 » April 15th, 2017, 9:02 am wrote:Correcting your elementary algebra mistake is appreciated, but could you shed light on why Einstein believed in causality and GR is said to be causal, when so much of the Universe events cannot possibly be causal according to SR and GR?

SR and GR are perfectly causal and deterministic. This is why these are included in the category of classical physics. The non-deterministic aspects of physics are found in quantum physics and it is chaotic dynamics which brings that indeterminism into the macroscopic realm.

What is "the interval s" or Δs?

That is the spatial version which we were classifying into null, space-like, or time-like from the beginning of the thread. It represents how distances are measured and its generalization in differential form is more important in GR, known as the metric. The ds in SR is known as the Minkowsky Metric and GR changes this, adding curvature, by putting functions of the space time coordinates in front of each term. Though since proper time is so closely related, the metric is often specified that way also (e.g. Wikipedia article on the Schwarzschild metric, though that one is in spherical coordinates).
User avatar
mitchellmckain
Member
 
Posts: 387
Joined: 27 Oct 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby rajnz00 on April 15th, 2017, 8:17 pm 

Getting back to fundamental concepts -Space-Time - it’s not generally known that while Einstein in his SR specified that space and time were relative he did not draw the conclusion that space and time were components of a single fabric. That was done by Minkowski. In fact, when Minkowski first came out with it, Einstein dismissed it as "superfluous learnedness". Only later when he realised that a lot of things fell into place when so computed, he adopted it as his own.

Having a look at Four-dimensional Minkowski space-time, with its static cone of "physical reality", containing static "worldlines", one can only conclude that the future is already there and the past exists. which is the reason why Einstein believed that, and which is the same reason why I think it is wrong. There must be another explanation which both explains space-time and proves it false.

Two questions sprung to my mind:
1. In Minkowski's 2-D space-time diagram, a beam of light emitted at the origin along the x axis towards positive values of x bisects the quadrant formed by ct-axis and x-axis, does this assume that space and time are moving at the same rate? If so, why should this be true? (From the point of view of expanding space)
2. Why should space and time be linked in the first place? What if time were independent of space?

Doing a search on my second question I came up with this: "Scientists suggest spacetime has no time dimension..without using time as the fourth dimension of spacetime, the physical world can be described more accurately."

"The concept of time as the fourth dimension of space – as a fundamental physical entity in which an experiment occurs – can be falsified by an experiment in which time does not exist. An example of such an experiment is the Coulomb experiment. Mathematically, this experiment takes place only in space.

“Minkowski space is not 3D + T, it is 4D,” the scientists write in their most recent paper. “The point of view which considers time to be a physical entity in which material changes occur is here replaced with a more convenient view of time being merely the numerical order of material change. This view corresponds better to the physical world and has more explanatory power in describing immediate physical phenomena: gravity, electrostatic interaction, information transfer by EPR experiment are physical phenomena carried directly by the space in which physical phenomena occur.”
As the scientists added, the roots of this idea come from Einstein himself.
“Einstein said, ‘Time has no independent existence apart from the order of events by which we measure it,’” Sorli told PhysOrg.com. “Time is exactly the order of events: this is my conclusion.”
In the future, the scientists plan to investigate the possibility that quantum space has three dimensions of space, as Sorli explained."
http://www.australianscience.com.au/phy ... dimension/
rajnz00
Member
 
Posts: 243
Joined: 28 Dec 2016


Re: Questions about Space, Time, Motion, Blackholes and Stuf

Postby BurtJordaan on April 16th, 2017, 3:41 am 

rajnz00 » 16 Apr 2017, 02:17 wrote:Having a look at Four-dimensional Minkowski space-time, with its static cone of "physical reality", containing static "worldlines", one can only conclude that the future is already there and the past exists.

Worldlines are not static, but are traced out by objects moving through 4-D spacetime. So it leaves a trace in its past, but its future is indeterminate.

In Minkowski's 2-D space-time diagram, a beam of light emitted at the origin along the x axis towards positive values of x bisects the quadrant formed by ct-axis and x-axis, does this assume that space and time are moving at the same rate?

Objects or effects move through spacetime. The only sense in which spacetime 'moves' is when we consider two reference frames that move relative to each other, with the operative word the unified 'spacetime', not 'space and time'.

Doing a search on my second question I came up with this: "Scientists suggest spacetime has no time dimension..without using time as the fourth dimension of spacetime, the physical world can be described more accurately."

Spacetime is a unified concept and in many models the math makes no distinction between space and time - they are treated equally. To make sense out of the world, we need to choose a sensible dimension of the 4-D to represent time, but the structure of the 4-D spacetime does not really care whether we can make sense out of it or not.

Going back to Newton's concept of time, as you suggested earlier, takes us some distance back towards the 'dark ages' - many observations become unexplainable using Newton's concept of time.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2256
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Next

Return to Metaphysics & Epistemology

Who is online

Users browsing this forum: No registered users and 8 guests