# Where did Einstein say :mass curve space/time ?

1. Dec 6, 2009

### heldervelez

I'm reading GR on http://www.bartleby.com/173/29.html" [Broken]
quoting "Hereupon we introduce a hypothesis: that the influence of the gravitational field on measuring-rods, clocks and freely-moving material points continues to take place according to the same laws, even in the case when the prevailing gravitational field is not derivable from the Galileian special case, simply by means of a transformation of co-ordinates."

My interpretation of "the influence of the gravitational field on measuring-rods, clocks and freely-moving material points" is : our rulers are not constant at all, because they are influenced by gravitational fields.

What he wrote there seems quite different from the usual "masses curve space/time". It appears that it is nothing about space but all about mass changes (non-rigid bodies).

http://www.bartleby.com/173/28.html" [Broken]
quoting
"The form there used (in SR) , “All bodies of reference K, K', etc., are equivalent for the description of natural phenomena (formulation of the general laws of nature), whatever may be their state of motion,” cannot be maintained, because the use of rigid reference-bodies, in the sense of the method followed in the special theory of relativity, is in general not possible in space-time description. The Gauss co-ordinate system has to take the place of the body of reference. The following statement corresponds to the fundamental idea of the general principle of relativity: “All Gaussian co-ordinate systems are essentially equivalent for the formulation of the general laws of nature.”"

From those Einstein sentences I read : NON rigid-bodies. The measuring rods and clocks are then 'elastic' in a predetermined way of beeing of course (GR way).

According to the way Einstein wrote, as I see it, he is not describing changes in space but changes in 'matter'.

COLOR="DarkOrange"](in SR)[/COLOR] is my note because of the context of the sentence.

Last edited by a moderator: May 4, 2017
2. Dec 6, 2009

### bcrowell

Staff Emeritus
I don't think it really matters whether Einstein said a certain thing. What matters is (a) the theory's internal self-consistency, (b) its relationship to empirical observations, and (c) whether it is simple enough to be usable as a guide to understanding what's going on. If you want to interpret GR as a theory under which material objects are distorted by externally imposed strains, then you're going back to what Lorentz and Fitzgerald tried to do before Einstein published the special theory in 1905. That type of interpretation fails all three tests above.

3. Dec 7, 2009

### A.T.

For a quantitative prediction of what will a ruler measure it is irrelevant if the the ruler is contracted or if the space between the measured points has expanded. The read off from the ruler will be the same in both cases, and that is all that matters in physics. The rest is philosophical interpretation.

4. Dec 7, 2009

### Ich

That's not an error, it's simply the definition of SR. "Special" means special covariance.
As to the flat background spcetime: it's unobservable, and iirc there are some issues concerning the complete mapping from curved to flat, including problems with coordinate singularites. This has been discussed here recently (I can't find where exactly).

5. Dec 7, 2009

### heldervelez

The last 2 posts by 'Bob_for_short' and 'Ich' are out of topic.

In the OP I quoted the Einstein words (Twice !).
In other threads we can focus on other issues.

Mr bcrowel said 'I don't think it really matters whether Einstein said ...then you're going back to what Lorentz..That type of interpretation fails all three tests above.'
Mr A.T. said '...quantitative prediction...it is irrelevant if the the ruler is contracted or ...philosophical interpretation.'

Latter I will discuss the interpretations of mr bcrowel and A.T. For now I intend to wait to see if there are any other answers.

The OP question remains: Where did Einstein said : mass curve space/time ?

Last edited: Dec 7, 2009
6. Dec 7, 2009

### Orion1

$$G_{\mu \nu} + \Lambda g_{\mu \nu}= {8 \pi G\over c^4} T_{\mu \nu}$$

Reference:
"people.uncw.edu/hermanr/Einstein/Legacy.ppt"[/URL]
[PLAIN]http://en.wikipedia.org/wiki/General_relativity" [Broken]

Last edited by a moderator: May 4, 2017
7. Dec 7, 2009

### heldervelez

Mr Orion1 the sentence you quote is from John Archibald Wheeler as we can see http://en.wikipedia.org/wiki/General_relativity" [Broken]:
" Paraphrasing the relativist John Archibald Wheeler, spacetime tells matter how to move; matter tells spacetime how to curve.[33]"

By coincidence it is in the same link you provide that we can see that the famous sentence is not from Einstein.

I do not question the validity of the field equation of GR. But by itself it is does not contradict the words of Einstein quoted in the OP.

I agree with Einstein, words and math, but reading its words it becames clear that not all of us have the same concepts. It seem that we (as a collective) are reluctant to accept his words.

The OP question remains.

Last edited by a moderator: May 4, 2017
8. Dec 7, 2009

### Ich

No. It's the whole point of this discussion whether GR is a geometric theory or not. It is.
This concept seems more appropriate for a congregation than a scientific community. For those who will only believe in his word, here's a quote from his 1916 paper:
So you see, it's space and time, not rods and clocks. With the caveat that this decision is a philosophical one, as has been mentioned by several posters in this and other threads.

9. Dec 7, 2009

### Fredrik

Staff Emeritus
I think this sounds like the version of GR that's been brought up a few times before by people who read Kip Thorne's "Black holes and time warps: Einstein's outrageous legacy". That book mentions that there's a version of GR that treats spacetime as flat and all the "geometry" stuff as being about deformations of measurement devices instead.

I got the impression that the two versions of the theory make identical predictions about the results of experiments. If that's the case, then it's a matter of taste if we're going to talk about them as two different but equivalent theories, or as two different formulations of the same theory. Thorne doesn't say much about that theory/formulation, except that it exists and that it's a useful way to think when you deal with a certain type of problems.

The people who brought this up here were asking where they could read more about it, and no one who replied could answer that. I'm surprised that Einstein was one of the people who described things in those terms.

10. Dec 7, 2009

### heldervelez

GR is not geometry. The unreality of metric. Space and time are subjective

IMO geometric theory is about mathematics.
If in doubt see http://bartleby.com/173/1.html" [Broken]
GR is not a geometric theory as you said, but instead is a physical theory (how to model the world : mass, space, measures, rods, clocks,..etc..)
http://en.wikipedia.org/wiki/Metric" [Broken]

But I do understood you, because of this: http://en.wikipedia.org/wiki/Metric_expansion_of_space" [Broken] but, read inside: "The metric expansion of space is the averaged increase of metric (i.e. measured) distance between distant objects in the universe with time."

And measured with what ? a physical rod.

again from Einstein (1916) ( bottom of pag 11 ? ) :
"The introduction of a system of reference serves no other purpose than to facilitate the description of the totality of such coincidences"

Any 'system of reference', metric space, etc... are abstract constructions. They do not belong to the reality. As an example is like make to a draw with CAD and have the grid visible. Is like make a polar plot in a paper with a polar grid already there.

Again from Einstein 1916 in the same page "That this requirement of general co-variance, which takes away from space and time the last remnant of physical objectivity,..."

If space and time are not objective than they are subjective (i.e. dependent of the observer)

Again from Einstein 1916 in the same page "The general laws of nature are to be expressed by equations which hold good for all systems of co-ordinates, that is, are co-variant with respect to any substitutions whatever..."

Then analysing his words "We now examine the influence exerted by the field of the mass M upon the metrical properties of space" upon the meaning of "metrical properties of space" must be read "upon the clock rating and rod lengths"

Such things as 'metric' or 'topology' are out of the reality.
They are abstractions and a help to our mind.

It is like this : Lets do some object (reality) counting (measure)
and I will use a binary metric and you a decimal metric (convenient abstractions).

after all this reasoning I do maintain the quest:
Where did Einstein said :mass curve space/time ?

Last edited by a moderator: May 4, 2017
11. Dec 7, 2009

### heldervelez

I do not know nothing on Kip...(nor black holes for the time beeing) rsrs...

I'm reading only Lorentz and Einstein papers, and trying to understand them is a challenge to me.

12. Dec 7, 2009

### Fredrik

Staff Emeritus
Kip Thorne's book talks about all the cool stuff, like black holes, wormholes and time travel, and it does all of that without math. It's an awesome book, written for people like you, so you should at least check it out.

If it's history you're interested in, then keep reading Lorentz and Einstein, but if you're just trying to learn the theory, there are much better ways.

13. Dec 8, 2009

### Ich

How come I'm feeling so tired?

14. Dec 9, 2009

### heldervelez

Re: Where did Einstein said :mass curve space/time ?

To me ...it really matters whether Einstein said..., but its only my opinion.
Just reading as Einstein wrote it, and stumbled with forced interpretations that 'space curves'.

What three tests ? above? I see none.