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Gravitational Constant Same Over Time

slo1
Posts: 4,316
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3/25/2014 10:03:12 AM
Posted: 2 years ago
Exploding stars prove Newton's law of gravity unchanged over cosmic time
http://www.sciencedaily.com...


Australian astronomers have combined all observations of supernovae ever made to determine that the strength of gravity has remained unchanged over the last nine billion years. Newton's gravitational constant, known as G, describes the attractive force between two objects, together with the separation between them and their masses. It has been previously suggested that G could have been slowly changing over the 13.8 billion years since the Big Bang. But researchers have now analyzed the light given off by 580 supernova explosions in the nearby and far Universe and have shown that the strength of gravity has not changed.
slo1
Posts: 4,316
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3/25/2014 10:13:05 AM
Posted: 2 years ago
I need some help on this one. I don't quite have a grasp of how this conclusion comes together.

How are we measuring the mass of the supernova at the point it explodes to know that G is the same then as now?

I assume if G was weaker it would require more mass or if it were stronger it would require less mass to generate the explosion. Is that right?
Subutai
Posts: 3,172
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3/25/2014 11:12:10 AM
Posted: 2 years ago
At 3/25/2014 10:13:05 AM, slo1 wrote:
I need some help on this one. I don't quite have a grasp of how this conclusion comes together.

How are we measuring the mass of the supernova at the point it explodes to know that G is the same then as now?

I assume if G was weaker it would require more mass or if it were stronger it would require less mass to generate the explosion. Is that right?

The force of the supernova is greater than the force of gravity, meaning that everything flies apart. The force of gravity is given by F = (Gm1m2)/r^2, where m1 and m2 are two separate objects with a specified mass, and G, of course, is the gravitational constant. A non-equilibrium sum of forces (meaning the forces to not add to zero) mean that there is some sort of acceleration on the body, because F=ma.

You can predict where the remnants of a supernova would end up by putting all of these values into an astronomical model. The only thing that supposedly varies is G, so by taking different values of G, they found that all the supernovae across most of the universe's history experienced a force proportional to that constant, and that it hasn't changed.

If G was weaker, the force of gravity would be weaker, and the supernovae would be further apart. Conversely, if G was stronger, the force of gravity would be stronger, and the supernovae would be closer together.
I'm becoming less defined as days go by, fading away, and well you might say, I'm losing focus, kinda drifting into the abstract in terms of how I see myself.
Subutai
Posts: 3,172
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3/25/2014 11:18:15 AM
Posted: 2 years ago
At 3/25/2014 11:12:10 AM, Subutai wrote:
At 3/25/2014 10:13:05 AM, slo1 wrote:
I need some help on this one. I don't quite have a grasp of how this conclusion comes together.

How are we measuring the mass of the supernova at the point it explodes to know that G is the same then as now?

I assume if G was weaker it would require more mass or if it were stronger it would require less mass to generate the explosion. Is that right?

The force of the supernova is greater than the force of gravity, meaning that everything flies apart. The force of gravity is given by F = (Gm1m2)/r^2, where m1 and m2 are two separate objects with a specified mass, and G, of course, is the gravitational constant. A non-equilibrium sum of forces (meaning the forces to not add to zero) mean that there is some sort of acceleration on the body, because F=ma.

You can predict where the remnants of a supernova would end up by putting all of these values into an astronomical model. The only thing that supposedly varies is G, so by taking different values of G, they found that all the supernovae across most of the universe's history experienced a force proportional to that constant, and that it hasn't changed.

If G was weaker, the force of gravity would be weaker, and the supernovae would be further apart. Conversely, if G was stronger, the force of gravity would be stronger, and the supernovae would be closer together.

Also, after a cursory reading of the article, I found this:

"...assumed that these supernova explosions happen when a white dwarf reaches a critical mass or after colliding with other stars to 'tip it over the edge'. This critical mass depends on Newton's gravitational constant G..."

I think the above still holds as well.
I'm becoming less defined as days go by, fading away, and well you might say, I'm losing focus, kinda drifting into the abstract in terms of how I see myself.
Sswdwm
Posts: 1,398
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3/25/2014 11:28:12 AM
Posted: 2 years ago
At 3/25/2014 11:12:10 AM, Subutai wrote:
At 3/25/2014 10:13:05 AM, slo1 wrote:
I need some help on this one. I don't quite have a grasp of how this conclusion comes together.

How are we measuring the mass of the supernova at the point it explodes to know that G is the same then as now?

I assume if G was weaker it would require more mass or if it were stronger it would require less mass to generate the explosion. Is that right?

The force of the supernova is greater than the force of gravity, meaning that everything flies apart. The force of gravity is given by F = (Gm1m2)/r^2, where m1 and m2 are two separate objects with a specified mass, and G, of course, is the gravitational constant. A non-equilibrium sum of forces (meaning the forces to not add to zero) mean that there is some sort of acceleration on the body, because F=ma.

You can predict where the remnants of a supernova would end up by putting all of these values into an astronomical model. The only thing that supposedly varies is G, so by taking different values of G, they found that all the supernovae across most of the universe's history experienced a force proportional to that constant, and that it hasn't changed.

If G was weaker, the force of gravity would be weaker, and the supernovae would be further apart. Conversely, if G was stronger, the force of gravity would be stronger, and the supernovae would be closer together.

Actually it's a bit more complicated than that:

The supernova investigated ate type 1a supernova, which result when a white dwarf accumulates mass which pushes it beyond the Chandrasekhar limit, reigniting fusion in an explosive manner. (and exceptionally uniform manner, making them good standard candles) http://en.wikipedia.org...

This limit is determined by the pressure inside of the white dwarf, in the same manner our sun gradually gets brighter as the core slowly collapses in on itself.

Therefore, the greater the G constant, the greater the internal pressure of the star/white drarf, the brighter stars will be and also the lower the Chandrasekhar limit will be.

.... At least that's the theory i think, I don't quite understand how they verified that G didn't change. It looks like they made some assumptions regarding the vacuum energy constant, but hopefully someone can double check this.

Older paper with better explanation in the intro:
http://link.springer.com...
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Vis13
Posts: 27
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3/27/2014 3:17:00 PM
Posted: 2 years ago
At 3/25/2014 11:12:10 AM, Subutai wrote:
At 3/25/2014 10:13:05 AM, slo1 wrote:
I need some help on this one. I don't quite have a grasp of how this conclusion comes together.

How are we measuring the mass of the supernova at the point it explodes to know that G is the same then as now?

I assume if G was weaker it would require more mass or if it were stronger it would require less mass to generate the explosion. Is that right?

The force of the supernova is greater than the force of gravity, meaning that everything flies apart. The force of gravity is given by F = (Gm1m2)/r^2, where m1 and m2 are two separate objects with a specified mass, and G, of course, is the gravitational constant. A non-equilibrium sum of forces (meaning the forces to not add to zero) mean that there is some sort of acceleration on the body, because F=ma.

You can predict where the remnants of a supernova would end up by putting all of these values into an astronomical model. The only thing that supposedly varies is G, so by taking different values of G, they found that all the supernovae across most of the universe's history experienced a force proportional to that constant, and that it hasn't changed.

If G was weaker, the force of gravity would be weaker, and the supernovae would be further apart. Conversely, if G was stronger, the force of gravity would be stronger, and the supernovae would be closer together.

Only if we suppose the classic limit, in the general theory of relativity, the gravity is discribe like the curvature of the space-time caused by the presence of mass in the local region.
Moreover, in quantum theory of field, the gravity would be the flow of many virtual particles. But this hypothesis isn't really verified...
Ragnar_Rahl
Posts: 19,297
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3/27/2014 5:21:52 PM
Posted: 2 years ago
I don't claim to understand. Therefore, I refer to a proxy consideration I can understand. Did they hypothesize that they would get this result before they did anything?
It came to be at its height. It was commanded to command. It was a capital before its first stone was laid. It was a monument to the spirit of man.