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Author Topic:   What is "the fabric" of space-time?
Straggler
Member (Idle past 201 days)
Posts: 10332
From: London England
Joined: 09-30-2006


Message 284 of 327 (473568)
06-30-2008 6:23 PM
Reply to: Message 276 by cavediver
06-29-2008 6:52 PM


Re: ?????
There is actually a far far simpler explanation

I read this and was pathetically optimistic that I would be able to understand.

As you may know, photons actually have no "length", as the proper distance between the emission and absorption of a photon is zero (think of infinite length contraction), and there is no time between emission and absorption (think of infinite time dilation.)

As "particle" travelling at the speed of light this makes sense in terms of my understanding of SR. So far so good.

So how does the red-shift arise in this context?

That is the question I am asking. So again I am optimistic regarding my comprehension.

It is simply a result of the light-cone at emission pointing in a different direction to the light cone at absorption. The photon allows us to overlap the light cones (despite being separated in our minds by billions of years and billions of light-years) and take a measurement of the difference between them.

I am lost :(
How do we take a measurment of the difference between light cones?
I can envisage the emission light cone. Ditto the absorption light cone. I can even imagine the merging of the two to form two cones base to base.

But I am utterly lost as to how this relates to the red shift?
Can you explain further?


This message is a reply to:
 Message 276 by cavediver, posted 06-29-2008 6:52 PM cavediver has replied

Replies to this message:
 Message 285 by cavediver, posted 06-30-2008 7:11 PM Straggler has taken no action

  
Straggler
Member (Idle past 201 days)
Posts: 10332
From: London England
Joined: 09-30-2006


Message 312 of 327 (475056)
07-13-2008 7:58 AM
Reply to: Message 310 by john6zx
07-13-2008 6:05 AM


Re: the gravity of general relativity
You seem to be saying that by trapping and condenscing pure energy in the absence of any matter new matter will be created..........

According to you pure energy, of whatever form, can be condensed to form a lump of uranium, for example?

Is this what you are saying?
If so do you have any examples of this sort of thing actually occurring?


This message is a reply to:
 Message 310 by john6zx, posted 07-13-2008 6:05 AM john6zx has replied

Replies to this message:
 Message 315 by john6zx, posted 07-13-2008 5:35 PM Straggler has replied

  
Straggler
Member (Idle past 201 days)
Posts: 10332
From: London England
Joined: 09-30-2006


Message 317 of 327 (475156)
07-13-2008 6:08 PM
Reply to: Message 315 by john6zx
07-13-2008 5:35 PM


Re: the gravity of general relativity
I am not saying that we have the ability to gather energy and make matter, I am saying that matter is a condensed form of energy.

Regardless of whether or not we have the technology to actually do so in practise, what you seem to be saying is that it is in principle possible to condense any form of energy into matter?

If so this is just wrong.

Can we agree that this universe is made up of matter and energy?

Time and space? Fields? What are black holes in your view?

Please just research MATTER on the web or in your books and tell me what you find

I don't find any mention of matter being a "condensed form of energy". My guess is that this misapprehension of the equivalance principle and resulting interpretation is uniquely your own.
Can you provide a source for this specific assertion of yours? Namely that "matter is a condensed form of energy".


This message is a reply to:
 Message 315 by john6zx, posted 07-13-2008 5:35 PM john6zx has replied

Replies to this message:
 Message 321 by john6zx, posted 07-13-2008 7:11 PM Straggler has replied

  
Straggler
Member (Idle past 201 days)
Posts: 10332
From: London England
Joined: 09-30-2006


Message 320 of 327 (475164)
07-13-2008 6:47 PM
Reply to: Message 319 by john6zx
07-13-2008 6:33 PM


Re: the gravity of general relativity
The whole point of the demonstration is to show that massive objects warp this thing called space-time, and gravity is not the cause of the planets orbits

No No No. The demo is a model of how the force of gravity can be considered in terms of spacetime curvature.

Nobody is saying that gravity does not exist. Gravity is the effect of spacetime curvature. GR provides a geometric explanation of what actually underlies the force of gravity.

Is this really scientific proof of the existance of space-time?

No it is a classroom model used for explanatory purposes. In the same way I can model the solar system with a bowling ball, an orange and some grapes nobody is claiming this is "proof" of the structure of the solar system!!!

Please explain where this demo proves beyond a reasonable doubt that space is a physical thing?

The demo proves nothing and is not intended to prove anything.
Evidence for GR comes in the form of gravitational lensing, GPS satellite time differences etc. etc. etc.

Predicted calculated results that have been experimentally verified. Repeatedly.


This message is a reply to:
 Message 319 by john6zx, posted 07-13-2008 6:33 PM john6zx has replied

Replies to this message:
 Message 324 by john6zx, posted 07-13-2008 8:16 PM Straggler has replied

  
Straggler
Member (Idle past 201 days)
Posts: 10332
From: London England
Joined: 09-30-2006


Message 323 of 327 (475168)
07-13-2008 7:36 PM
Reply to: Message 321 by john6zx
07-13-2008 7:11 PM


Fundamental Particles
Here is one web site of many that talks about the relationship between matter and energy.

In other words the assertion that "matter is a condensed form of energy" is not supported at all and is in fact an interpretation borne of your misapprehension of the equivalence principle.

I am familiar with the equivalence principle. I have no doubt that there is a relationship between energy and matter.
However nowhere will you find that your assertion "matter is a condensed form of energy" is a valid conclusion of the equivalence principle.

You are just wrong with regard to this.

What are atoms made of?

Protons, neutrons and electrons. To the best of our knowledge neutrons and protons are themselves comprised of quarks which are fundamental particles.

What are electrons?

Negatively charged fundamental particles.

What is matter really made of?

Fundamental particles and the various quantised force carrier 'particles' associated with the 4 fundamental forces.

It may be the case that various fundamental particles can be derived from multidimensional strings 'vibrating' at different 'frequencies'. Or there may be another basis for the various properties of the different fundamental particles. Time will tell.

You have not mentioned what you think matter is made of, but I think by the time we boil this whole subject down we will have our answer.

Matter is not made of energy. Energy is a property of matter. We need to get past this erroneous assertion of yours before any progress can be made.


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Straggler
Member (Idle past 201 days)
Posts: 10332
From: London England
Joined: 09-30-2006


Message 326 of 327 (475175)
07-13-2008 8:44 PM
Reply to: Message 324 by john6zx
07-13-2008 8:16 PM


GR - One of the Most Verified Theories in Science
Which is it? Is gravity a force? Or some geometric curvature of space-time?

Gravity is a force borne from spacetime curvature.
GR is the theory of gravity as spacetime curvature.

As you are such a wiki fan - from Wiki

General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the state-of-the art description of gravity in modern physics. It unifies special relativity and Newton's law of universal gravitation, and describes gravity as a property of the geometry of space and time, or spacetime

John writes

In order for this whole idea of space-time to make any logical sense there would have to be some evidence that this fabric actually exists. There is none. So why is it even taken seriously?

The whole GPS satellite system relies on the curvature of spacetime and the calculations that are derived from this view of spacetime as a curved "fabric".

There is no direct evidence in the existance of this space-time fabric.

As someone who is so fond of Wiki I would suggest that you look up General Realtivity and the verification of it in terms of the numerous observed effects of spacetime curvature. It has been repeatedly experimentally verified. From as far back as 1915 but most famously in 1919.

From Wiki

Similarly, a 1919 expedition led by Eddington confirmed general relativity's prediction for the deflection of starlight by the Sun,[7] making Einstein instantly famous.[8] Yet the theory entered the mainstream of theoretical physics and astrophysics only with the developments between approximately 1960 and 1975, now known as the Golden age of general relativity. Physicists began to understand the concept of a black hole, and to identify these objects' astrophysical manifestation as quasars.[9] Ever more precise solar system tests confirmed the theory's predictive power,[10] and relativistic cosmology, too, became amenable to direct observational tests.[11]

John says

If space is not a real physical thing where does that leave GR and SR? So there must be some direct evidence in the idea that space is a real physical thing.

Spacetime can hardly curve if it is not a physical thing now can it?
If space is not physical how can it curve?
If it does not curve how do you explain the extremely accurate and repeatable predictions of GR that are used by every sat nav system in the world?
Your alterantive theory will need to at least match the predictive power of GR.

Good luck.


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