Inertial and gravitational mass

  • B
  • Thread starter Geo
  • Start date
  • #1
Geo
10
1

Main Question or Discussion Point

Doesn't the postulation of the inertial and gravitational mass equivalence suggest that GR is not a complete theory? (since it also cannot be explained as a neccessity by the anthropic principle)
 

Answers and Replies

  • #2
berkeman
Mentor
56,133
6,165
Doesn't the postulation of the inertial and gravitational mass equivalence suggest that GR is not a complete theory? (since it also cannot be explained as a neccessity by the anthropic principle)
Can you post links to the previous PF threads that you have read through about this, and ask specific questions about that reading that you are having trouble understanding? Thanks.
 
  • #3
Geo
10
1
Can you post links to the previous PF threads that you have read through about this, and ask specific questions about that reading that you are having trouble understanding? Thanks.
I should have posted on beyond the standard model or general relativity.

It is just seems to me paradoxical for a theory to postulate an axiom that is subject of the microscopic and at the same time offer no bridge from the microscopic to the larger scale. Also the equivalence of inertial mass and gravitational mass shouldnt suggest that there is a hidden cause for this coincedence or one of the two is emergent?

(I cant point it to something i read it is just a question that popped and i wanted to know if it shouldnt for some reason or if it something that bothers the scientific community. Sorry if i am being silly i am just curious)

Thank you for your reply!
 
  • #4
28,558
4,865
suggest that GR is not a complete theory
Why should a physical theory be complete? What scientific problem does it solve or cause? I just don’t see why it matters
 
  • #5
Geo
10
1
Why should a physical theory be complete? What scientific problem does it solve or cause? I just don’t see why it matters
It solves the problem of progress i think, if you can see a bigger part of the picture you can make better guesses that will turn out to be confirmed by experiments. And after all as Feynman may have said (or may not actually couldn't find source) "physics is like sex sure it may give some practical result but that's not why we do it"
 
  • #6
Geo
10
1
Seeing the bigger picture and searching for it when it is possible isnt enough of a reason to do science?
 
  • #7
27,152
7,333
Doesn't the postulation of the inertial and gravitational mass equivalence suggest that GR is not a complete theory?
GR doesn't "postulate" the equivalence of inertial and gravitational mass. That is a prediction of GR, not a postulate of it.
 
  • #8
28,558
4,865
It solves the problem of progress i think, if you can see a bigger part of the picture you can make better guesses that will turn out to be confirmed by experiments.
I don’t think there is any reason to believe this claim. Einstein didn’t make good guesses or see the bigger picture because previous theories were complete. Nor did anyone else as far as I can tell.

Seeing the bigger picture and searching for it when it is possible isnt enough of a reason to do science?
Sure, it is a fine reason. It is just not connected to completeness.
 
Last edited:
  • #9
Geo
10
1
I don’t think there is any reason to believe this claim. Einstein didn’t make good guesses or see the bigger picture because previous theories were complete. Nor did anyone else as far as I can tell.

Sure, it is a fine reason. It is just not connected to completeness.
My claim wasn't that completion as a state is what matters like a switch, if it was expressed that way my bad. My claim is that the hunt for completion and each step towards it is something that matters. So by saying a theory is incomplete the issue that arises is not why a theory should be complete but that if a theory is incomplete maybe there is more to discover in that direction. A fundamental driving force of science is the path towards completion. So to say that something is incomplete is important because a question is being asked and either is answered in the frame of the theory and move towards completion or the aproach changes. Einstein in order to get to his theories he tried to answer the right questions and in order for the right question to exist there must be uneasiness towards incompletion
 
  • #10
28,558
4,865
My claim is that the hunt for completion and each step towards it is something that matters. ... A fundamental driving force of science is the path towards completion.
I don’t think that there is any evidence to support any of these claims either. Where are you getting this stuff?

So to say that something is incomplete is important
Any theory that uses basic arithmetic and numbers is inherently incomplete! That is simply not a big concern amongst physicists. Philosophers and mathematicians may worry about it, but physicists just go ahead and use arithmetic anyway.

Einstein in order to get to his theories he tried to answer the right questions and in order for the right question to exist there must be uneasiness towards incompletion
No, his goal was not to solve the incompleteness of Newtonian physics. Relativity is incomplete in the same way as all other physical theories.

You may be confusing unification with completeness. It is a good goal to unify explanations, but completeness is not a desideratum for physical theories.
 
  • #11
Geo
10
1
In my view It is. The fact that is unachieavble doesn't matter. Tha fact that you don't get there even with infinite steps doesn't matter. Completion as an impossible state is irrelevant but the steps towards it is partly how science is built within the mathematical framework from axioms to theorems to more theorems (this discovery of the consequances of axiomatization is a path towards completion ) and for the truths that cant be investigated inside the frame you create new frame. Unification in a preexisting framework is path towards completeness. Also physics isn't exactly a formal system to just accept that every completeness is impossible because interpretations assign scientific values to theorems and so does incompleteness. The fact that there is a shut up and calculate subgroup doesnt neccesserily dictate that interpetions are purely phillosophical. Physics after all was about explaining the world the minimal approach is usefull when things get complicated but doesnt strip physics from interpretations just assumes that it can also work without them
 
  • #12
28,558
4,865
In my view It is.
So far you haven’t shown any evidence to support your view. Do you have any professional scientific reference that takes this stance, or a historical example that supports it?

Tha fact that you don't get there even with infinite steps doesn't matter. Completion as an impossible state is irrelevant but the steps towards it is partly how science is built
This doesn’t make any sense. You cannot make steps towards completeness. A theory is either complete or it is incomplete. And as Goedel proved any theory using arithmetic is incomplete. Physicists as a whole simply don’t care. I can cite every single theory using arithmetic despite its incompleteness.

Can you cite any professional physicist working on completeness? Again, I think you are confusing completeness with unification or universality.

Completeness is something different. It means that every true statement within a theory can be proven from the axioms of the theory. Read about Goedels incompleteness theorems. Even just basic arithmetic on the natural numbers is incomplete. All physical theories are built on arithmetic and are incomplete. I don’t know of any efforts by physicists to “fix” that.

At this point you have done nothing but speculate. If you wish to continue this discussion then please post a professional scientific reference that explains what you are talking about. I strongly suspect you mean something else than what is meant by “complete” in the sense of Goedels theorem.
 
  • #13
Geo
10
1
Yes i am familliar with goedels theorems and that's why i ve stated that completeness is impossible. But that is irrelevant because i didnt meant it in goedels terms. Physics as a whole is not a formal system so the word completion can be used in a way that don't have to meet goedels criteria.
Even in goedel's term my point was that incompletence theorem is irrelevant because if you dont know that the certain truth i pointed out is unprovable within the formal system then proving it is not a task that you should not undertake

I should have used another word to avoid confusion and i am sorry for that, it is just that i didn't consider goedel's theorems relevant that made me continue. My fault
 
  • #14
28,558
4,865
But that is irrelevant because i didnt meant it in goedels terms.
Please provide a reference that shows the sense in which you did mean it then. We have now wasted a lot of effort talking past each other.
 
  • #15
kimbyd
Science Advisor
Gold Member
2018 Award
1,137
586
Doesn't the postulation of the inertial and gravitational mass equivalence suggest that GR is not a complete theory? (since it also cannot be explained as a neccessity by the anthropic principle)
No. The equivalence of gravitational and inertial mass doesn't necessarily need any explanation.

The real problems with General Relativity are two-fold:
1) General Relativity predicts regions of space-time that it cannot describe. This concept is known as "geodesic incompleteness". For example, General Relativity predicts a singularity at the center of a black hole, but you can't actually use a map that includes the singularity and still provides sensible results (in essence, including the singularity means you end up dividing by zero at some point). But GR definitely shows the paths of objects can intersect with this region it can't describe.
2) General Relativity is incompatible with quantum mechanics. Quantum mechanics allows objects to be in a superposition of states. General Relativity uses a definition of matter that assumes that there's no such thing as a superposition. Mathematical attempts to extend General Relativity to allow for quantum effects have proven to be mathematically challenging (the methods used for the electromagnetic field, for instance, just don't work).
 
  • Like
Reactions: Geo
  • #16
281
54
Yes i am familliar with goedels theorems and that's why i ve stated that completeness is impossible. But that is irrelevant because i didnt meant it in goedels terms. Physics as a whole is not a formal system so the word completion can be used in a way that don't have to meet goedels criteria.
Even in goedel's term my point was that incompletence theorem is irrelevant because if you dont know that the certain truth i pointed out is unprovable within the formal system then proving it is not a task that you should not undertake

I should have used another word to avoid confusion and i am sorry for that, it is just that i didn't consider goedel's theorems relevant that made me continue. My fault
People on this forum like to be precise about definitions when it comes to science and math, and for good reason. Lay definitions tend to lead to confusion and wasted posts. E.g., my post. :P
 
  • #17
TeethWhitener
Science Advisor
Gold Member
1,532
840
What’s missing here is a definition of complete. @Dale is invoking Godel, for which “complete” had a precise technical meaning (a formal system is complete iff all valid statements in that system are provable). @Geo seems to be using complete in a non-technical sense, such that the meaning attached to the word is vague. Maybe if you give us a more precise formulation, we can help you more.
 
  • #18
pervect
Staff Emeritus
Science Advisor
Insights Author
9,583
854
Doesn't the postulation of the inertial and gravitational mass equivalence suggest that GR is not a complete theory? (since it also cannot be explained as a neccessity by the anthropic principle)
I don't follow the argument at all. The anthropic principle is a philsophical principle, not a scientific one:

wiki said:
The anthropic principle is a philosophical consideration that observations of the Universe must be compatible with the conscious and sapient life that observes it.
I've seen the argument that Newtonian theory isn't complete, because Newtonian theory puts the equivalence down to "coincidence".

GR, to the extent it defines "mass" at all, doesn't bother to distinguish between the "inertial" and "gravitaitonal" mass. So it doesn't make any sense to me to claim that GR is incomplete on this basis. It makes some sense ot me to say that Newtonian physics isn't complete, on this basis, but that's not the claim.

I also suspect that completeness of a theory is also a philosphical issue. So we have two philosphical issues, one of which I don't see has any relevance at all (the anthropic principle), and the other of which appears to be being applied backwards from the usual statement.

This isn't a good start for a philosophicall discussion, which as I recall aren't supposed to happen on PF anyway - due to their tendency to be of low academic quality. This one seems well on the route to becoming a low-quality philosophical discussion already :(.
 
  • #19
Nugatory
Mentor
12,425
4,908
I've seen the argument that Newtonian theory isn't complete, because Newtonian theory puts the equivalence down to "coincidence".
I think you're right that that's the sort of thing people are thinking about when they casually use the word "incomplete". It would be better to call these open questions, and if having them makes a physical theory incomplete, then all theories are incomplete - ask enough "why?" questions and we always end up with "just because that's how the universe we live in works".
 
  • Like
Reactions: Geo
  • #20
Geo
10
1
I don't follow the argument at all. The anthropic principle is a philsophical principle, not a scientific one:



I've seen the argument that Newtonian theory isn't complete, because Newtonian theory puts the equivalence down to "coincidence".

GR, to the extent it defines "mass" at all, doesn't bother to distinguish between the "inertial" and "gravitaitonal" mass. So it doesn't make any sense to me to claim that GR is incomplete on this basis. It makes some sense ot me to say that Newtonian physics isn't complete, on this basis, but that's not the claim.

I also suspect that completeness of a theory is also a philosphical issue. So we have two philosphical issues, one of which I don't see has any relevance at all (the anthropic principle), and the other of which appears to be being applied backwards from the usual statement.

This isn't a good start for a philosophicall discussion, which as I recall aren't supposed to happen on PF anyway - due to their tendency to be of low academic quality. This one seems well on the route to becoming a low-quality philosophical discussion already :(.
Anthropic reasoning is at least relevant as long as cosmology and/or string theory are relevant. Anthropic reasoning is not a metaphysical construct, is logical reasoning and as such is used in scientific papers and theories by scientists.
(Witten and Susskind to mention two who at least have referenced it)
https://arxiv.org/abs/hep-th/0302219

I can understand that it may be debatable in the community. And is a very abused and misused term but what i did is to state that anthropic explanations dont apply, so if you don't agree with it you can just dismiss that part and nothing changes on the initial post

P.s. sorry if my use of english is bad, it's not my native language

Thanks for the answers!
 
  • #21
28,558
4,865
Still no reference regarding completeness in the sense you mean it?
 
  • #22
Geo
10
1
I misused the word in the way that Nugatory explained. I would rephrase my question to that: Is the equivalence of gravitational and inertial mass something that is bothering the scientific community or explaining it as: "that's the way the universe works" is all we got and there is no evidence or reasoning that suggest otherwise?
 
  • #23
28,558
4,865
Is the equivalence of gravitational and inertial mass something that is bothering the scientific community
As @pervect said, it bothered people in Newtonian gravity, but that bother is resolved in GR.
 
  • Like
Reactions: Geo
  • #24
A.T.
Science Advisor
9,800
1,604
Is the equivalence of gravitational and inertial mass something that is bothering the scientific community...
The scientific community should be bothered that it isn't more complicated?
 
  • #25
Nugatory
Mentor
12,425
4,908
I misused the word in the way that Nugatory explained. I would rephrase my question to that: Is the equivalence of gravitational and inertial mass something that is bothering the scientific community or explaining it as: "that's the way the universe works" is all we got and there is no evidence or reasoning that suggest otherwise?
The equivalence of gravitational and inertial mass in Newtonian gravity was something that bothered the scientific community, and even Newton himself. Why should they be the same? The universe works this way, but why? There's no answer in Newtonian gravity.

However, Einstein's general relativity provides a satisfactory explanation, so the question is no longer a major concern.
 

Related Threads for: Inertial and gravitational mass

  • Last Post
Replies
13
Views
3K
Replies
9
Views
549
  • Last Post
Replies
18
Views
554
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
9
Views
3K
  • Last Post
Replies
5
Views
2K
Replies
22
Views
3K
Replies
20
Views
15K
Top