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Clarification on Gravity

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TheEngineer

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Re: Clarification on Gravity
« Reply #930 on: February 11, 2009, 09:24:43 AM »
Read the first post in this thread, please.
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bowler

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Re: Clarification on Gravity
« Reply #931 on: February 11, 2009, 09:52:00 AM »
I have, which is why its all about interpretation. Some say gravity blurred the distinction between a force and a fictitious force, others say it is a fictitious force. Most of the blurring comes from the fact the other fictitious forces are don't use curvilinear coordinates. I fall into the former camp. Its like arguing over whether an electron is a particle or whether an electron is a wave. If there was no matter of interpretation the gravity could not be thought of as a particle exchange force except that it can. My personal suspicion is that we are looking at the emergence of something similar to the particle wave duality question in quantum mechanics. Kaluza and Klein showed electromagnetism could be geometric and no end of people have quantized gravity. I think we are seeing glimpses of something very fundamental though my maths isn't good enough to see what.
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TheEngineer

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Re: Clarification on Gravity
« Reply #932 on: February 11, 2009, 09:53:09 AM »
Quote from: TheEngineer on February 11, 2009, 09:24:43 AM
Read the first post in this thread, please.
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cbarnett97

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Re: Clarification on Gravity
« Reply #933 on: February 11, 2009, 09:54:50 AM »
Quote from: TheEngineer on February 11, 2009, 04:50:08 AM
Quote from: cbarnett97 on February 11, 2009, 02:59:18 AM
the same people who jump all over you for using the term gravity probably go to the butcher and have no problem ordering 2 pounds of meat.
I have no problem doing that.   :-\ 

I do love my porterhouses...
So you are wrong when you order then
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bowler

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Re: Clarification on Gravity
« Reply #934 on: February 11, 2009, 10:07:34 AM »
Now im bored of this as well. Wheres Matrix gone.
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TheEngineer

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Re: Clarification on Gravity
« Reply #935 on: February 11, 2009, 10:47:08 AM »
Quote from: cbarnett97 on February 11, 2009, 09:54:50 AM
So you are wrong when you order then
How so?

Quote from: bowler on February 11, 2009, 10:07:34 AM
Now im bored of this as well. Wheres Matrix gone.
Typical RE'er.  Runs away when he is shown his error.
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"I haven't been wrong since 1961, when I thought I made a mistake."
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bowler

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Re: Clarification on Gravity
« Reply #936 on: February 11, 2009, 10:51:57 AM »
I was bored because you referred me to the same post, thats pretty much a debating no no. To be honest if you dont believe me thats fine. Though makes you wonder what they fill the quantum gravity journals with. Im not even disagreeing with what you say. Im just saying its one interpretation but not the only one. Its just as incomplete as the others.
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TheEngineer

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Re: Clarification on Gravity
« Reply #937 on: February 11, 2009, 11:29:21 AM »
If you had read the first post the first time, I would not have sent you to the same post twice.  But you still don't seem to be able to understand, which is a debating no-no.
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"I haven't been wrong since 1961, when I thought I made a mistake."
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cbarnett97

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Re: Clarification on Gravity
« Reply #938 on: February 11, 2009, 12:19:45 PM »
Quote from: TheEngineer on February 11, 2009, 10:47:08 AM
Quote from: cbarnett97 on February 11, 2009, 09:54:50 AM
So you are wrong when you order then
How so?

Quote from: bowler on February 11, 2009, 10:07:34 AM
Now im bored of this as well. Wheres Matrix gone.
Typical RE'er.  Runs away when he is shown his error.
A pound is a unit of weight now?
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markjo

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Re: Clarification on Gravity
« Reply #939 on: February 11, 2009, 12:30:33 PM »
Quote from: cbarnett97 on February 11, 2009, 12:19:45 PM
Quote from: TheEngineer on February 11, 2009, 10:47:08 AM
Quote from: cbarnett97 on February 11, 2009, 09:54:50 AM
So you are wrong when you order then
How so?

Quote from: bowler on February 11, 2009, 10:07:34 AM
Now im bored of this as well. Wheres Matrix gone.
Typical RE'er.  Runs away when he is shown his error.
A pound is a unit of weight now?

It sure is.
Quote from: http://en.wikipedia.org/wiki/Weight#The_pound_and_other_non-SI_units
In United States customary units, the pound can be either a unit of force or a unit of mass.
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cbarnett97

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Re: Clarification on Gravity
« Reply #940 on: February 11, 2009, 12:33:34 PM »
Quote from: markjo on February 11, 2009, 12:30:33 PM
Quote from: cbarnett97 on February 11, 2009, 12:19:45 PM
Quote from: TheEngineer on February 11, 2009, 10:47:08 AM
Quote from: cbarnett97 on February 11, 2009, 09:54:50 AM
So you are wrong when you order then
How so?

Quote from: bowler on February 11, 2009, 10:07:34 AM
Now im bored of this as well. Wheres Matrix gone.
Typical RE'er.  Runs away when he is shown his error.
A pound is a unit of weight now?

It sure is.
Quote from: http://en.wikipedia.org/wiki/Weight#The_pound_and_other_non-SI_units
In United States customary units, the pound can be either a unit of force or a unit of mass.
But it is not technically correct, it was agreed by convention that it can be used as both
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niceguybut

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Re: Clarification on Gravity
« Reply #941 on: February 11, 2009, 12:34:49 PM »
Quote from: TheEngineer on February 11, 2009, 09:24:43 AM
Read the first post in this thread, please.

Dunno whether that was directed at me or bowler (I'm assuming bowler given the subsequent exchanges, but you never know), but I was just trying to summarise in an admittedly very simplistic way what was in the first post, partly with the aim of making sure I had understood everything, but also that you might be able to use to steer people in the right direction before laying the heavy (no pun intended) stuff on them.  Not having studied any pure physics for well over twelve years now, aside from some structural mechanics, I'm trying to make sure I understand the principles of what's being discussed.

Sorry for rambling, and feel free to tell me where I'm wrong (preferably without insults).
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Dr Matrix

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Re: Clarification on Gravity
« Reply #942 on: February 11, 2009, 01:18:06 PM »
I've missed a bit of debate here so I'll just go ahead and make some idle observations which people can then argue with me about.

1) You can transfer into a flat spacetime frame in a gravitational field... All you have to do is not apply any additional forces to yourself as you jump off a roof and as far as you're concerned there is no gravitational interaction going on at all, despite being in what would normally be considered 'curved' spacetime to an external observer (assuming, of course, that your own mass is negligible and that you can be treated as a pointlike object).  Einstein himself said that this was "the happiest thought of his life", when he realised that inertial observers do not experience gravitation.  All experiments performed by inertial observers must agree according to relativity, so therefore none of them can feel anything that the others do not - the only valid solution is that they all feel nothing.

2) I'm sorry if I missed any equations that came up, bowler.

3) A general distinction between 'gravity' and 'gravitation' is that gravity refers to the Newtonian concept of 'invisible springs' pulling bodies together, wheres gravitation is more usually applied when talking about GR/curved spacetime (I make the distinction in the latter since GR is not the only theory of gravitation that utilises curved spacetime).

4) It's nice to be missed.

Any questions?
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hyppolito

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Re: Clarification on Gravity
« Reply #943 on: February 11, 2009, 01:39:42 PM »
It seems a little foolhardy to make declarative statements about general relativity when one has not played with the guts of it, i.e. Ricci curvature and Einstein's field equations. 
As Lord Kelvin said,

"In physical science the first essential step in the direction of learning any subject is to find principles of numerical reckoning and practicable methods for measuring some quality connected with it. I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be."
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Dr Matrix

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Re: Clarification on Gravity
« Reply #944 on: February 11, 2009, 01:54:29 PM »
hyppolito - I think you'll find there are several people here who have 'played around with the guts' of GR, so throwing around the names of a couple of tensor equations isn't going to give you much currency.  Also, Lord Kelvin was a bit of a twat - don't get me wrong, here did great work - but he grossly underestimated the importance of a good physical intuition.  Let's not forget that many great discoveries, not least relativity, were initially born from thought experiments with no calculation involved whatsoever.
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Quote from: Arthur Schopenhauer
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
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hyppolito

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Re: Clarification on Gravity
« Reply #945 on: February 11, 2009, 02:08:15 PM »
Quote from: Matrix on February 11, 2009, 01:54:29 PM
hyppolito - I think you'll find there are several people here who have 'played around with the guts' of GR, so throwing around the names of a couple of tensor equations isn't going to give you much currency.  Also, Lord Kelvin was a bit of a twat - don't get me wrong, here did great work - but he grossly underestimated the importance of a good physical intuition.  Let's not forget that many great discoveries, not least relativity, were initially born from thought experiments with no calculation involved whatsoever.

A twat Lord Kelvin may be, but it does not invalidate his statement.  There is certainly a place for intuition as a starting point, but without math it's just not science.  Also, I'm not buying it on faith that flat earthers also happen to be really good at tensor analysis.     
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Dr Matrix

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Re: Clarification on Gravity
« Reply #946 on: February 11, 2009, 02:23:54 PM »
Quote from: hyppolito on February 11, 2009, 02:08:15 PM
A twat Lord Kelvin may be, but it does not invalidate his statement.  There is certainly a place for intuition as a starting point, but without math it's just not science.  Also, I'm not buying it on faith that flat earthers also happen to be really good at tensor analysis.    

His being a bit of a twat - he wasn't that bad - isn't what I took objection to.  That fact is more the result of his dismissal of the importance of a physical intuition.  Maths is important in formulating theories and making predictions, but in terms of actually generating new ideas it is useless.  Maths is a tool, not a means unto itself - without a physical interpretation it is a cold, meaningless abstraction of nature that will leave you numerically correct, but no wiser.

I've argued this point many times with theorists and mathematicians who place maths at the top of the 'league table' of science in terms of 'purity'... typically maths-physics-chemistry-biology.  Maths can be a very interesting pursuit, but I maintain that as a science in its own right it will never describe the Universe in any meaningful way without a physical interpretation.  As a result, it is a tool - a very beautifully crafted, infinitely intricate and versatile swiss army knife for the physicist to use when MacGuyvering humanity's view of the Universe.
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Quote from: Arthur Schopenhauer
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
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niceguybut

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Re: Clarification on Gravity
« Reply #947 on: February 11, 2009, 02:25:00 PM »
Hmm, dunno where my original reply to this went, but I'll try again.

Quote from: Matrix on February 11, 2009, 01:18:06 PM
1) You can transfer into a flat spacetime frame in a gravitational field... All you have to do is not apply any additional forces to yourself as you jump off a roof and as far as you're concerned there is no gravitational interaction going on at all, despite being in what would normally be considered 'curved' spacetime to an external observer (assuming, of course, that your own mass is negligible and that you can be treated as a pointlike object).  Einstein himself said that this was "the happiest thought of his life", when he realised that inertial observers do not experience gravitation.  All experiments performed by inertial observers must agree according to relativity, so therefore none of them can feel anything that the others do not - the only valid solution is that they all feel nothing.

So in other words someone watching someone else jump off a roof would see the same thing on RE and FE, therefore this experiment is invalid as proof of either?

Quote from: Matrix on February 11, 2009, 01:18:06 PM
3) A general distinction between 'gravity' and 'gravitation' is that gravity refers to the Newtonian concept of 'invisible springs' pulling bodies together, wheres gravitation is more usually applied when talking about GR/curved spacetime (I make the distinction in the latter since GR is not the only theory of gravitation that utilises curved spacetime).

Fair enough, but I stick by my definition on the previous page for the noob wanting the simplest possible differentiation.  Either way, I agree that Newton never bothered about why gravitation occurred, only concerning himself with observing its effects.

Quote from: Matrix on February 11, 2009, 01:18:06 PM
4) It's nice to be missed.

Aye, I've missed insulting Yorkshire...
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"The Zetetic Astronomy has come into my hands ... if it be childish, it is clever; if it be mannish, it is unusually foolish."

A Budget of Paradoxes - A. de Morgan (pp 306-310)
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bowler

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Re: Clarification on Gravity
« Reply #948 on: February 11, 2009, 02:26:19 PM »
I'm not denying that gravity can be viewed as a fictitious force, that is the most common interpretation used today. I still don't think that gravity can always be removed by a simple frame change, though I think you can show this by applying a rotating frame to the minkowski metric. Though thats a small point anyway. My bigger issue is the one of interpretation. Strictly we can't tell the difference between gravity and a fictitious force. Obviously for everyday this makes no difference. But as far as fundamental physics is concerned it is of crucial importance. Is this true for all forces at some level? Kaluza and Klein did this for electromagnetism.

Im interested in BSM (Beyond Standard Model) physics and for this the nature of gravity at a more fundamental level, I guess I'd say im trying to discuss how we'll see gravity at the end of the 21st century not at the end of the 20th century because we know it isn't complete. I must confess some ignorance to gravity i've not studied GR beyond undergrad level so I can't really prove much more than that GR shows that gravity cannot be distinguished from a fictitious force. Im more interested in weak interactions which about as far from gravity as you can get (though it is a regime where GR will not work). Though its important to remember that the equivalence principle means that gravity can be seen as a fictitious force, doesn't mean it is one, not that it matters if it is. Another perfectly valid way of looking at this is that Einstein has just opened up the definition of force to debate. Really the choices are endless, i'm not trying to answer a question, I'm simply trying to open the thread to the depth of the question.
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Dr Matrix

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Re: Clarification on Gravity
« Reply #949 on: February 11, 2009, 02:40:54 PM »
Quote from: niceguybut on February 11, 2009, 02:25:00 PM
So in other words someone watching someone else jump off a roof would see the same thing on RE and FE, therefore this experiment is invalid as proof of either?

Correct :)

Bloody northerners... ;)

Quote from: bowler on February 11, 2009, 02:26:19 PM
My bigger issue is the one of interpretation. Strictly we can't tell the difference between gravity and a fictitious force.

This was the point I was making before, possibly in another thread - you can tell the difference with GR, you just have to make a very, very sensitive experiment and work very, very hard to get a detectable signal.  Frame dragging and things like the optical Aharonov-Bohm effect are examples of things that cannot be explained by the 'fictitious force' analogy.

Quote from: bowler on February 11, 2009, 02:26:19 PM
Im interested in BSM (Beyond Standard Model) physics and for this the nature of gravity at a more fundamental level, I guess I'd say im trying to discuss how we'll see gravity at the end of the 21st century not at the end of the 20th century because we know it isn't complete [...] Really the choices are endless, i'm not trying to answer a question, I'm simply trying to open the thread to the depth of the question.

I think you said it best - there are endless possibilities that only good experiments and open debate can guide us through.  Why do you think I argue for the side of FET these days?
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Quote from: Arthur Schopenhauer
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
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hyppolito

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Re: Clarification on Gravity
« Reply #950 on: February 11, 2009, 02:42:55 PM »
Quote from: Matrix on February 11, 2009, 02:23:54 PM
Quote from: hyppolito on February 11, 2009, 02:08:15 PM
A twat Lord Kelvin may be, but it does not invalidate his statement.  There is certainly a place for intuition as a starting point, but without math it's just not science.  Also, I'm not buying it on faith that flat earthers also happen to be really good at tensor analysis.    

His being a bit of a twat - he wasn't that bad - isn't what I took objection to.  That fact is more the result of his dismissal of the importance of a physical intuition.  Maths is important in formulating theories and making predictions, but in terms of actually generating new ideas it is useless.  Maths is a tool, not a means unto itself - without a physical interpretation it is a cold, meaningless abstraction of nature that will leave you numerically correct, but no wiser.

I've argued this point many times with theorists and mathematicians who place maths at the top of the 'league table' of science in terms of 'purity'... typically maths-physics-chemistry-biology.  Maths can be a very interesting pursuit, but I maintain that as a science in its own right it will never describe the Universe in any meaningful way without a physical interpretation.  As a result, it is a tool - a very beautifully crafted, infinitely intricate and versatile swiss army knife for the physicist to use when MacGuyvering humanity's view of the Universe.

Kelvin did not dismiss intuition, he saw it as a first step towards understanding.  For example, he developed his electrostatic water drop experiment and it had to be on intuition because the theory of charge was not sufficiently developed to predict a behavior like that at the time.   However, he was not content to leave it at a qualitative observation. 
Do you see math as an invention?  That seems to be what you are suggesting, and I have questions if that's the case.
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niceguybut

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Re: Clarification on Gravity
« Reply #951 on: February 11, 2009, 02:50:22 PM »
Quote from: Matrix on February 11, 2009, 02:40:54 PM
Bloody northerners... ;)

Southern fairies :P

Quote from: bowler on February 11, 2009, 02:26:19 PM
My bigger issue is the one of interpretation. Strictly we can't tell the difference between gravity and a fictitious force.

I refer the honourable gentlemen to the simplistic definition I gave earlier, that gravitation is the cause, and gravity is the effect.  As I say, I'm not a physicist, so am only trying to get the layman interpretation of what's happening.  I can build from there.
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"The Zetetic Astronomy has come into my hands ... if it be childish, it is clever; if it be mannish, it is unusually foolish."

A Budget of Paradoxes - A. de Morgan (pp 306-310)
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Dr Matrix

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Re: Clarification on Gravity
« Reply #952 on: February 11, 2009, 02:53:18 PM »
Quote from: hyppolito on February 11, 2009, 02:42:55 PM
Kelvin did not dismiss intuition, he saw it as a first step towards understanding.  For example, he developed his electrostatic water drop experiment and it had to be on intuition because the theory of charge was not sufficiently developed to predict a behavior like that at the time.   However, he was not content to leave it at a qualitative observation. 
Do you see math as an invention?  That seems to be what you are suggesting, and I have questions if that's the case.

I didn't say he dismissed it, I said he dismissed its importance. There is a subtle but important difference there.

As for maths, I don't view it as an invention, I view it as something that seems fundamental in its nature, but being fundamental does not mean that if you knew all of maths that you would "Know the mind of God", to quote Einstein.  I see maths as a means to an end, not the end in its own right.
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Quote from: Arthur Schopenhauer
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
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hyppolito

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Re: Clarification on Gravity
« Reply #953 on: February 11, 2009, 03:11:36 PM »
Quote from: Matrix on February 11, 2009, 02:53:18 PM
Quote from: hyppolito on February 11, 2009, 02:42:55 PM
Kelvin did not dismiss intuition, he saw it as a first step towards understanding.  For example, he developed his electrostatic water drop experiment and it had to be on intuition because the theory of charge was not sufficiently developed to predict a behavior like that at the time.   However, he was not content to leave it at a qualitative observation. 
Do you see math as an invention?  That seems to be what you are suggesting, and I have questions if that's the case.

I didn't say he dismissed it, I said he dismissed its importance. There is a subtle but important difference there.

As for maths, I don't view it as an invention, I view it as something that seems fundamental in its nature, but being fundamental does not mean that if you knew all of maths that you would "Know the mind of God", to quote Einstein.  I see maths as a means to an end, not the end in its own right.

The example covers either interpretation.  If he dismissed the importance of intuition, he wouldn't be using it.  What does "fundamental in its nature" mean? Fundamental in itself?
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TheEngineer

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Re: Clarification on Gravity
« Reply #954 on: February 11, 2009, 03:13:56 PM »
Quote from: cbarnett97 on February 11, 2009, 12:19:45 PM
A pound is a unit of weight now?
It has been for some time now...
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niceguybut

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Re: Clarification on Gravity
« Reply #955 on: February 11, 2009, 03:19:39 PM »
Quote from: TheEngineer on February 11, 2009, 03:13:56 PM
Quote from: cbarnett97 on February 11, 2009, 12:19:45 PM
A pound is a unit of weight now?
It has been for some time now...

Only in the US, where not everyone in the world lives...
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"The Zetetic Astronomy has come into my hands ... if it be childish, it is clever; if it be mannish, it is unusually foolish."

A Budget of Paradoxes - A. de Morgan (pp 306-310)
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TheEngineer

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Re: Clarification on Gravity
« Reply #956 on: February 11, 2009, 07:47:56 PM »
Sucks for them.
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cbarnett97

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Re: Clarification on Gravity
« Reply #957 on: February 11, 2009, 07:51:20 PM »
Quote from: TheEngineer on February 11, 2009, 03:13:56 PM
Quote from: cbarnett97 on February 11, 2009, 12:19:45 PM
A pound is a unit of weight now?
It has been for some time now...
So if you write a report you write that you started with 2 kilograms which weghed 19.6 kilograms?  ::)
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TheEngineer

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Re: Clarification on Gravity
« Reply #958 on: February 11, 2009, 07:54:20 PM »
Sorry, but me and the butcher are not having a scientific discussion.  I know that to him, pound means pound force.  To me, a pound of porterhouse means a pound force of buttery deliciousness.
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        -- Bob Hudson
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TheEngineer

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Re: Clarification on Gravity
« Reply #959 on: February 11, 2009, 07:55:25 PM »
Quote from: cbarnett97 on February 11, 2009, 07:51:20 PM
Quote from: TheEngineer on February 11, 2009, 03:13:56 PM
Quote from: cbarnett97 on February 11, 2009, 12:19:45 PM
A pound is a unit of weight now?
It has been for some time now...
So if you write a report you write that you started with 2 kilograms which weghed 19.6 kilograms?  ::)
It would be nice if you could keep your units straight.  Maybe that is why all your arguments suck so badly...
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"I haven't been wrong since 1961, when I thought I made a mistake."
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