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Pushing gravity


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Showing 1-25 of 37 posts in this discussion
Initial post: Jan 13, 2013, 4:28:19 AM PST
[Deleted by the author on Mar 28, 2013, 2:37:05 PM PDT]

Posted on Jan 13, 2013, 5:01:24 AM PST
tom kriske says:
What, in your view, is wrong with the theory of gravity that we have?

The author of the above linked book: Matthew R. Edwards studied biology, biochemistry and plant ecology at McMaster University, York University and the University of Saskatchewan. Since 1983 he has been at the Gerstein Science Information Centre of the University of Toronto. He has diverse research interests and has been the author of several articles on cosmology and the origin and early evolution of life.

Yes, he seems to be eminently qualified to write a scholarly treatise on gravitational physics. As for the 'Gerstein Science Information Center' -- It's a library!!

Posted on Jan 13, 2013, 5:11:11 AM PST
[Deleted by the author on Mar 28, 2013, 2:37:11 PM PDT]

In reply to an earlier post on Jan 13, 2013, 5:35:41 AM PST
tom kriske says:
You asked if anyone has looked into any alternative theories of gravity, and I asked what's wrong with the one we have. So, grifter, what is wrong with the one we have?

In reply to an earlier post on Jan 13, 2013, 6:21:14 AM PST
Actually a quantum theory of gravity, one which would model gravity as a quantum field, would be one in which gravity acts via exchange of gravitons, spin-2 bosons, and these would pervade space. However, no one has been able to figure out how to do that in a way which can be experimentally confirmed. It remains one of the biggest unsolved problems in physics.

In reply to an earlier post on Jan 13, 2013, 6:22:41 AM PST
The theory of gravity we have now, general relativity, works fine as far as we know in every situation but two: during the Planck era of the Big Bang, and inside black holes. In each case a realm is encountered in which gravity can no longer be ignored on the microscopic scale because of very high energy density, requiring a quantum theory of gravity to accurately describe what's going on.

In reply to an earlier post on Jan 13, 2013, 6:40:41 AM PST
tom kriske says:
arp, why are you explaining this to me?

In reply to an earlier post on Jan 13, 2013, 8:06:02 AM PST
Because you asked another poster what in his view was wrong with the theory of gravity we already have.

In reply to an earlier post on Jan 13, 2013, 9:19:23 AM PST
tom kriske says:
yes, the operative phrase being 'another poster', and what was 'his' view. But while we're on it, what's your take on the mathematics underlying the canonical quantization of general relativity? Specifically, there is every reason to suspect that the correct quantization procedure needs to be background independent, but the existence of spin 2 gravitons is a purely background dependent, quantum field theoretical notion. Any insights?

In reply to an earlier post on Jan 13, 2013, 9:37:42 AM PST
Jeff Marzano says:
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In reply to an earlier post on Jan 13, 2013, 12:41:11 PM PST
You've officially exceeded my level of comprehension.

In reply to an earlier post on Jan 13, 2013, 12:42:06 PM PST
It's quite straightforward in principle. One either drastically reduces or drastically increases the mass of the object generating the gravitational field. Voila!

In reply to an earlier post on Jan 13, 2013, 12:55:37 PM PST
for one thing the current model does not work

In reply to an earlier post on Jan 13, 2013, 12:55:58 PM PST
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In reply to an earlier post on Jan 13, 2013, 12:56:28 PM PST
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In reply to an earlier post on Jan 13, 2013, 1:21:57 PM PST
Doctor Who says:
No, its irrelevant. Gravity is about 35 orders of magnitude smaller than electromagnetism.

"Irrelevant" is not the same as "fails"

In reply to an earlier post on Jan 13, 2013, 1:25:53 PM PST
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In reply to an earlier post on Jan 13, 2013, 1:26:18 PM PST
Doctor Who says:
How do you get that? There are no observations that contradict GR. We know Theoretically that it breaks down at the beginning of the universe and with massive quantum objects, however there is no experimental evidence that it actually does break down. This is probably an artifact due to a poor choice of math used to express the theory. When Newton's law of gravity was expressed as tensor calculus, you got GR. When GR is expressed in some type of field theory, you get a quantum theory of gravity. They only difference would occur at singular points in the current theory, not rewrite the current theory.

Remember, we have no trouble sending people to the moon, or even probes to Pluto, using the current model.

In reply to an earlier post on Jan 13, 2013, 1:28:00 PM PST
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In reply to an earlier post on Jan 13, 2013, 1:31:32 PM PST
Last edited by the author on Jan 13, 2013, 2:04:05 PM PST
Doctor Who says:
As I said before, it does not fail. It is irrelevant. You can use gravity in nuclear physics. It is just irrelevant since it is too weak to effect the physics.

"Anything less than exactly perfect is a FAIL"

This is completely wrong. I have some homework for you. I want to take an ordinary ruler and measure a CD case or something 10 times. Use an independent measurement each time, ie, don't force yourself to get the same answer. Is your result exactly the same? Or a better method: have 10 people do the same experiment and only compare notes at the end.

Spoiler: of course it isn't. An exact measurement is impossible. Any theory about CD cases could only be checked to within you ability to measure. Physics is an experimental science. If you can't measure it, it does not really matter.

EDIT: some numbers!
Proton mass: 1.67 e-27 kg
Electron mass: 9.109 e-31 kg
elemental charge: 1.602 e-19 coulombs

Assume a distance of 1 Bohr radius: 53 pm or 5.3 e −11 m

E&M attraction:

|F(E&M) | = k e^2 / r^2 = - 8.211 e-8 N
|F(G)| = G mM/r^2 = -0.0 N (I need a better calculator for this!) => |F(G)| = 3.5 e-51

So the electromagnetic force is about 10^40 times stronger. That is a 1 followed by 40 zeros, or 10 000 000 000 000 000 000 000 000 000 000 000 000 000 times smaller. Since its only possible to get 5 or 6 precise digits, who cares? You can't measure it. (by the way, this clearly gets worse for lighter particles)

In reply to an earlier post on Jan 13, 2013, 1:38:22 PM PST
Doctor Who says:
One possibility: string theory. All string theories in all formulations are forced to include a spin 2 boson that acts as a gravititon. What is more interesting, the theory has a known classical limit. This limit is GR exactly as one might expect.

A "limit", by the way, is a process of removing quantities that are too small to measure. For example, if I where to remove a nano meter from your CD case, your previous measurements would be unaffected. Since we can't measure any corrections string theory might add, we neglect them and say that within that limit GR is the correct theory.

A second possibility is quantum loop gravity, but has not yet produced a description of flat space. This is a problem.

You see, we have been working on this.

In reply to an earlier post on Jan 13, 2013, 2:14:43 PM PST
tom kriske says:
horse, please give us a specific example where general relativity has failed. In particular, give an example where the model made a prediction, and subsequent experiment failed to find said result.

In reply to an earlier post on Jan 13, 2013, 3:34:18 PM PST
General relativity predicts a point of infinite energy density at the "start" of the Big Bang and in the center of black holes. This is probably not correct.

In reply to an earlier post on Jan 13, 2013, 3:43:39 PM PST
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In reply to an earlier post on Jan 13, 2013, 3:54:01 PM PST
tom kriske says:
These 'predictions' though aren't meant to be predictive in the usual sense; they are meant to signal the point at which the theory no longer makes physical sense. In other words, those realms that are plagued by singularities are not within the domain of the model's purview, but rather serve to define its boundary. Interestingly though, those regions of spacetime that you mentioned are, quite possibly, not directly communicable to any external observers, and so represent...what...a place where the very act of experimentation fails to serve as an arbiter of scientific efficacy?
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Discussion in:  Science forum
Participants:  8
Total posts:  37
Initial post:  Jan 13, 2013
Latest post:  Jan 15, 2013

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