Albert Einstein's theory of gravity is generally explained in a wrong way

In summary, the article complains about how it's being popularly described to the layperson, not about the science itself. There are some confusing analogies to the common descriptions, notably the bowling ball / rubber sheet model. General relativity is the theory that explains how mass warps space-time, and it does so in a way that makes insanely accurate predictions about results of experiments.
  • #1
eggman89
4
0
Hello All

I have stumbled upon the following article while reading the Reviews of the Book The Road to Reality : A Complete Guide to the Laws of the Universe .
About the misrepresentation of Albert Einstein's theory of gravity.

The way many physicists explain Albert Einstein's theory of gravity in TV and DVD documentaries, the way they write about it in books for the general public raises many questions and requires clarification. ...
See link for details:
https://www.amazon.com/Albert-Einsteins-gravity-generally-explained/forum/Fx14E1SHOI9HI4W/Tx9H9JTV8GPVGR/1/ref=cm_cd_ef_rt_tft_tp?_encoding=UTF8&asin=0679454438&tag=pfamazon01-20

Although I am a computer engineer by profession, I am very must interested in physics.
But all my knowledge have come from the Popular Science books from Stephan Hawking and Roger Penrose books, along with few documentaries I have seen.

The quoted article does raise some very good question.
Could anyone explain that ? (Specially point no 3 and 5 )
 
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  • #2
You have neglected to cite the source, i.e. where did this review appear?

Any and all sources MUST be cited properly in this forum.

Zz.
 
  • #3
Post edited. Link provided.
 
  • #4
Another problem with the original post: Too much cuttin' and pastin'. We have rules against that.
 
  • #5
Just to be clear, the article is simply complaining about how it's being popularly described to the layperson, not about the science itself.

There are indeed some confusing analogies to the common descriptions, notably the bowling ball / rubber sheet model.

There are better ones out there. They're more accurate but less intuitive.
 
  • #6
I'm sorry for not adhering to the rules.
But I joined forum expecting answers to some of the questions I encountered.
All responses I'm getting is about forum rules instead of someone clarifying the actual questions.
It's not like I claimed these doubts to be mine. I had already mentioned the place where I had encountered the article. The reason I did not gave the link initially, because I thought it might be a dynamic link (which it was not).
By entirely pasting the article, I was hoping to save the effort to read it in a new a tab and come back here to reply.

Now someone please answer the questions. :)
 
  • #7
3. This guy doesn't seem to understand that terms like "force" are defined in each theory. They're certainly not defined in some God-given theory-independent way. In GR, space and time are represented by something called a "smooth manifold". The motion of a particle is represented by a curve in this manifold. The "straight lines" in the manifold represent non-accelerating motion. Acceleration is a measure of how badly the curve that represents the object's motion fails to be straight. Force is defined by F=ma, where a is acceleration. So if the object isn't accelerating (a=0), then by definition of "force", there's no force acting on it (F=0).

What you need to know in addition to that, is that particles in free fall are represented by those straight lines. In other words, the free-falling particles are not accelerating. This is one of the assumptions that defines general relativity, so it's not something we can prove mathematically, or by some sort of "logical" argument. I could argue that the straight lines are the only ones that really distinguish themselves mathematically, while the free-falling objects are the only ones that really distinguish themselves physically, but ultimately, the only thing that can justify the assumption is the fact that the theory defined this way makes insanely accurate predictions about results of experiments.

5. That analogy is pretty bad, so this guy is at least right about something. I've seen it discussed here many times before. They often talk about a bowling ball on a rubber sheet. You can do a search if you want to see what people have been saying about it.

7. This one is hilarious. How many high school kids know differential geometry?
 
  • #8
Now to deal with the objections raised in that review. First and foremost, it is a review by a customer, not a physicist.

1) How can space-time be warped?
We don't know.2) What makes the planets orbit the sun?
Newtonian physics: Mass causes an inverse square law force called gravitation. What makes that happen? We don't know. It just is. That gravitation is a force with some specific characteristics is axiomatic in Newtonian mechanics.

General relativity: Mass warps space-time. What makes that happen? We don't know. It just is. That mass does warp space-time in a very well-defined manner is axiomatic in general relativity.3) What about Newton's apple?
What about it? Here the author of the review is insisting that gravity must be a force. That is the Newtonian mechanics point of view.4) Double standard about what gravity is.
No double standard. Calling those fundamental interactions "forces" is a pop-sci representation. Quantum mechanics doesn't talk about forces. It talks about interactions. Force is a Newtonian physics concept. We call things like electromagnetism a force because that fits the Newtonian point of view. Things get weird in the quantum world. It is better to call electromagnetism an interaction rather than a force. This is even more so for the strong and weak interactions.5) The table cloth demonstration is flawed ...
Of course it is. It is an analogy. Analogies are always flawed in some regard, particularly so pop science analogies.

Pop science analogies are used even for Newtonian mechanics. Some mathematical background is required to get a detailed understanding of how gravity works in Newtonian mechanics. Without that knowledge one has to resort to simplifications and popular science explanations. The math needed to understand Newtonian gravitation (with appropriate simplifications) is high school level algebra / freshman level calculus.

On the other hand, detailed gravity models of the Earth such as those developed with thanks to satellites such as GRACE and GOCE are inaccessible to people with just a freshman level of understanding, and one is stuck with pop science explanations of what is going on.

Graduate level mathematics is needed to attain a true understanding of the general relativistic explanation of gravity. Without that knowledge true understanding is not possible. Pop sci explanations can be given, but these pop science explanations / analogies will inevitably leave some questions unanswered.6) Trying to reconcile unreconcilable interpretations ...
The author is of the comment is wrong. The explanations are not irreconcilable. In fact, if general relativity did not simplify to yield the same answers as does Newtonian mechanics in the domain of relatively small masses (the Sun is a relatively small mass) and relatively small velocities (tens of kilometers per second or less). Even in the case of Mercury, the deviation between Newtonian mechanics and general relativity is quite small: 43 arcseconds of precession per century. A second of arc is a very, very small angle.

Note that it is the predictions that have to be consistent between general relativity and Newtonian mechanics in the domain where Newtonian mechanics is known to be highly accurate. The mechanisms behind those predictions do not have to be consistent. The same goes for Newtonian mechanics versus quantum mechanics. Quantum mechanics must predict the same results for an experiment where we know that the Newtonian point of view works. That Newtonian mechanics and quantum mechanics take rather disparate paths to get to the very similar predicted results is irrelevant.7) Einstein's theory of gravity is not taught in middle and high schools
Well, duh. It's not taught to undergraduate physics majors either for the most part. The math is too complex.
 
  • #9
I agree that the presentation of GR, even in graduate texts is a bit skewed. Mind you, there is nothing wrong predictively with expressing gravity in GR as curved space-time. It is one direction of the equivalence principle but that principle is a two way identification.

In its strongest form, the equivalence principle manifests as the relativity of the geometry of space-time and dynamic gravity so that one can always choose a space-time geometry wherein explicit gravitational forces disappear and all gravitational effects are geometric effects, but that is just gauge condition! (and indeed the ultimate gauge condition.)

Specifically saying "gravity is just curved space-time" is invoking, in particular, a geometric model of gravity. Understanding that this is a model and not the theory itself if fine. One is not then making ontological assumptions about unobservable entities (e.g. the reality of space-time "fabric"). This sort of modeling is parallel to an aetheric model of SR's predictions as we had prior to Einstein's relativization, namely relativity of distance and duration manifested in that model as aetheric clock slowing and measuring rod contractions.

But it is only a model. It is more appropriate to invoke the full general relativity implied by the equivalence principle, and acknowledge a choice of geometry as a gauge condition. One then (in all but one set of cases) has a fixed space-time geometry with an explicit physical gravitational field along with electromagnetic and matter fields.

One would e.g. split the connection terms in the covariant derivatives as geometric + dynamic:
[tex] \Gamma^\alpha_{\mu\nu} = C^\alpha_{\mu\nu} + G^\alpha_{\mu\nu}[/tex]
(C for geometry, G for dynamic field).

Of course calculation wise, one is invoking a whole heap of ugly extra cross terms to contend with and one also will have to contend with the distinct forms "covariance" takes when considering geometric covariance vs geometric + gauge dynamic covariance. (This is something I've been meaning to work through and may jump back into it this summer since I'm not teaching...it ought to keep me out of too much mischief. )

There's really no point in this extra work at the classical level as it will not change prediction. That to me is the meaning of the equivalence principle in its strongest form. However...

Philosophically this more general perspective undermines the objective reality of space-time as a physical object. Pragmatically I believe this is a crucial step before attempting a quantum theory of gravity.
 
  • #10
Even classically there are different mathematical structures like curvature and torsion (or both) which lead to identical (or almost identical) physical predictions. So there are different models with identical (or almost identical) predictions. That means that talking about "gravity as curved spacetime" could be premature.
 
  • #11
@D_H and others

Thanks a lot. :)
Exactly what I was looking for.
 
  • #12
D H said:
7) Einstein's theory of gravity is not taught in middle and high schools
Well, duh. It's not taught to undergraduate physics majors either for the most part. The math is too complex.

Oh on the contrary! I was taught differential geometry on n-dimensional manifolds as an 8th grader after we finished our lessons on how to find the area of a rhombus.

The guy obviously has never even taken a serious physics course in his life.
 
  • #13
But Einstein was just an office clerk? So how hard can it be? :biggrin:
 

What is Albert Einstein's theory of gravity?

Albert Einstein's theory of gravity, also known as the theory of general relativity, is a scientific theory that explains the force of gravity as a result of the curvature of space-time caused by massive objects.

Why is it said that Einstein's theory of gravity is generally explained in a wrong way?

It is said that Einstein's theory of gravity is generally explained in a wrong way because many people tend to simplify or misinterpret the complex concepts and equations involved, leading to misunderstandings and misconceptions about the theory.

What are some common misconceptions about Einstein's theory of gravity?

Some common misconceptions about Einstein's theory of gravity include the idea that it is solely based on the concept of mass, that it only applies to objects in space, and that it has been proven to be completely accurate and infallible.

How does Einstein's theory of gravity differ from Newton's theory of gravity?

Einstein's theory of gravity differs from Newton's theory of gravity in several ways, including the fact that it takes into account the curvature of space-time, while Newton's theory only considers the force of gravity between objects based on their mass and distance.

What are some practical applications of Einstein's theory of gravity?

Einstein's theory of gravity has many practical applications, including predicting the motion of planets and other celestial bodies, explaining the phenomenon of gravitational lensing, and providing the basis for modern technologies such as GPS and gravitational wave detectors.

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