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galacsi
2008-Dec-07, 12:06 PM
I know some think that EM energy or light can act like mass and have a gravity effect.

It come from the famous formula : E = Mc2 taken as face value.

If E is the energy of some photons which can also expressed as E = h*nu you can compute a mass equivalent of light.

So light must attract matter , even if so lightly.

My question is : Is there any proof of that or is it a mathematical fantasy ?

Hornblower
2008-Dec-07, 12:51 PM
I know some think that EM energy or light can act like mass and have a gravity effect.

It come from the famous formula : E = Mc2 taken as face value.

If E is the energy of some photons which can also expressed as E = h*nu you can compute a mass equivalent of light.

So light must attract matter , even if so lightly.

My question is : Is there any proof of that or is it a mathematical fantasy ?I would say inference, not fantasy.

Absence of evidence is not necessarily evidence of absence. If a theory is in good agreement with phenomena that can be observed, and it predicts something that is too slight to be observed, I would invoke Occam's Razor and accept the prediction unless someone comes along with a finer instrument that can refute it. Then it would be back to the drawing board to revise the theory.

JohnD
2008-Dec-07, 12:58 PM
If any particle with mass is accelerated to c, then it acquires infinite mass.
So the photon is assumed to have zero mass.

But see: http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html
which discusses this better than I can. And Google for "photon mass" for manyother discussions.
JOhn

galacsi
2008-Dec-07, 02:31 PM
I would say inference, not fantasy.

Yes it is better worded.

Absence of evidence is not necessarily evidence of absence.

Can I use this citation ? In an other part of this forum ? :)

If a theory is in good agreement with phenomena that can be observed, and it predicts something that is too slight to be observed, I would invoke Occam's Razor and accept the prediction unless someone comes along with a finer instrument that can refute it. Then it would be back to the drawing board to revise the theory.

So no confirmation ?

galacsi
2008-Dec-07, 02:35 PM
If any particle with mass is accelerated to c, then it acquires infinite mass.
So the photon is assumed to have zero mass.

But see: http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html
which discusses this better than I can. And Google for "photon mass" for manyother discussions.
JOhn

Thanks for the link. It confirm what I knew on the subject of photon mass.

But this is not my question . Is light or EM energy has or has not a gravitational action ?

alainprice
2008-Dec-07, 02:55 PM
Firstly, E=mc2 applies to a single particle at rest.

If we use E2=p2c2 + m2c4 , we can apply it to a particle at rest or a particle which moves at c, where m is the rest mass of the particle and p is the linear momentum. This formula can be applied to any particle with any speed.

Secondly, do you mind explaining what differences would exist if light did not create a warping/stressing of spacetime? Are you curious or do plan to apply an idea?

cjameshuff
2008-Dec-07, 03:03 PM
Not EM, but analogous: the quarks of which protons are composed, which we can identify when we break protons apart in particle accelerators, add up to about 0.05 proton masses. 95% of the mass of a proton is in the binding energy holding the proton together, and the amount of mass agrees with what theory predicts that binding energy to be.

galacsi
2008-Dec-07, 03:06 PM
Firstly, E=mc2 applies to a single particle at rest.

If we use E2=p2c2 + m2c4 , we can apply it to a particle at rest or a particle which moves at c, where m is the rest mass of the particle and p is the linear momentum. This formula can be applied to any particle with any speed.

Secondly, do you mind explaining what differences would exist if light did not create a warping/stressing of spacetime? Are you curious or do plan to apply an idea?

Yes I am more than just curious. Well it is an ATM idea I got reading posts about black holes in this forum.So this is not the place.
I am reluctant to post about in the ATM subforum. You know the rules of this forum are from the wild west ,if you post an idea in the ATM forum , it is like a challenge to the mainstream who cannot let it go. You have to fight for it , answers all questions or be banned. Phew !

galacsi
2008-Dec-07, 03:08 PM
Not EM, but analogous: the quarks of which protons are composed, which we can identify when we break protons apart in particle accelerators, add up to about 0.05 proton masses. 95% of the mass of a proton is in the binding energy holding the proton together, and the amount of mass agrees with what theory predicts that binding energy to be.

Interesting , I did not know . Thanks !

grant hutchison
2008-Dec-07, 04:39 PM
Thanks for the link. It confirm what I knew on the subject of photon mass.

But this is not my question . Is light or EM energy has or has not a gravitational action ?It has. A box of photons masses more than an "empty" box. (Scare quotes on the "empty", since even an empty box will contain equilibrium radiation.)
We know that energetic photons are produced when matter and anti-matter annihilate. The photons contain the mass-energy of the original matter and anti-matter, and therefore would produce the same gravitational effect, if they could be suitably confined.

Grant Hutchison

mugaliens
2008-Dec-07, 08:12 PM
Is light or EM energy has or has not a gravitational action ?

Yes! Here's how (and towards the end, how much):

E=mc2 you already know, where E is the energy, m is rest mass, and c is the speed of light in a vacuum.

However, since a photon's rest mass = 0, does that mean that a photon has no gravitational attraction?

Not at all. It's rest mass may be 0, but a photon isn't at rest, is it!

Let's examine another equation, this one from quantum theory, specifically, Planck's theory of black-body radiation that explained the observed spectrum correctly. He determined that a photon has an energy, E, proportional to it's frequency, f:

E=hf

where h is Planck's constant. Since f=c/λ, where λ is the wavelength, the following holds true:

E=hc/λ

Let's go back to Einstein's equation and set these two equations equal to one another:

hc/λ=mc2

Solving for m, we get:

m=hc/λc2, or m=h/λc

Thus, a photon's "equivalent mass" is equal to Planck's constant divided by the product of of its wavelength and the speed of light.

Before you cry "Eureka!" however, let's put that into perspective. Very little mass was converted to energy for the Tsar Bomba blast - only a few pounds, at best. Yet that was the largest nuclear explosion ever detonated by mankind, and it was equivalent to the total energy output of the Sun for 1.4 seconds.

Thus, doing this in reverse, if we were to take the total energy output of the Sun for 1.4 seconds, and convert it to matter, you may have a couple of pounds. However, gravity is so pathetically weak, that the couple of pounds wouldn't get you very far with respect to all that photonic energy's gravitational effect on another body.

Let's upscale that to the Sun's photonic output for an entire year, which is 22.5 million times as much. Now you have a mass equivalent of about 50 million pounds, or 25,000 tons, which is the size of your average ocean-going freighter. If we put two of those puppies next to one another in the open reaches of space, with a distance of 100 m between their centers of mass, the force pulling them together would be given by:

F=Gm1m2/r2

Thus, F=6.6742e-11 * 22.680e6^2 / 100^2 = 3.4 kg.

About 7-1/2 lbs. That's how much gravitational attraction our Sun's photonic output for entire year would exert if it could be bottled up and set about 100 m away from an equivalent mass.

Bring your oven mitts...

galacsi
2008-Dec-08, 02:02 PM
Yes! Here's how (and towards the end, how much):

E=mc2 you already know, where E is the energy, m is rest mass, and c is the speed of light in a vacuum.

However, since a photon's rest mass = 0, does that mean that a photon has no gravitational attraction?

Not at all. It's rest mass may be 0, but a photon isn't at rest, is it!

Let's examine another equation, this one from quantum theory, specifically, Planck's theory of black-body radiation that explained the observed spectrum correctly. He determined that a photon has an energy, E, proportional to it's frequency, f:

E=hf

where h is Planck's constant. Since f=c/λ, where λ is the wavelength, the following holds true:

E=hc/λ

Let's go back to Einstein's equation and set these two equations equal to one another:

hc/λ=mc2

Solving for m, we get:

m=hc/λc2, or m=h/λc

Thus, a photon's "equivalent mass" is equal to Planck's constant divided by the product of of its wavelength and the speed of light.

Before you cry "Eureka!" however, let's put that into perspective. Very little mass was converted to energy for the Tsar Bomba blast - only a few pounds, at best. Yet that was the largest nuclear explosion ever detonated by mankind, and it was equivalent to the total energy output of the Sun for 1.4 seconds.

Thus, doing this in reverse, if we were to take the total energy output of the Sun for 1.4 seconds, and convert it to matter, you may have a couple of pounds. However, gravity is so pathetically weak, that the couple of pounds wouldn't get you very far with respect to all that photonic energy's gravitational effect on another body.

Let's upscale that to the Sun's photonic output for an entire year, which is 22.5 million times as much. Now you have a mass equivalent of about 50 million pounds, or 25,000 tons, which is the size of your average ocean-going freighter. If we put two of those puppies next to one another in the open reaches of space, with a distance of 100 m between their centers of mass, the force pulling them together would be given by:

F=Gm1m2/r2

Thus, F=6.6742e-11 * 22.680e6^2 / 100^2 = 3.4 kg.

About 7-1/2 lbs. That's how much gravitational attraction our Sun's photonic output for entire year would exert if it could be bottled up and set about 100 m away from an equivalent mass.

Bring your oven mitts...

Thanks for this long answer.

So it all depend if this mass equivalent is something actually existing. From your computation it is clear we have no way of testing it.

Black holes may give a way to test it if one consider matter inside one is destroyed and transformed in radiation.

That was my idea. If matter is transformed in radiation and radiation has no gravitational effect then may be the black hole cannot make it to the singularity point. It can reach an equilibrium or oscillate between different states or densities.
At a point , the more it eat the more it is lighter so to speak and it must burp the excess.
It may explain some behaviour of the monster !

If you are right there is no way it is possible . Too bad I like my pet idea !

JohnD
2008-Dec-08, 04:01 PM
That was my idea. If matter is transformed in radiation and radiation has no gravitational effect then may be the black hole cannot make it to the singularity point. It can reach an equilibrium or oscillate between different states or densities.
At a point , the more it eat the more it is lighter so to speak and it must burp the excess.
It may explain some behaviour of the monster !

If you are right there is no way it is possible . Too bad I like my pet idea !

Then from your previous posts, you imply that a black hole may lose mass by radiation.
Hawking got there before you, I fear, but the amount of mass lost by Hawking Radiation (HR) is inversely proprotional the BH mass and the radius of the event horizon. The bigger the BH, the less is lost, and the time for even a 'normal' BH (not a galaxy core one, nor a micro-BH) to decay by HR is more than the likely age of the Universe.

Are you thinking ogf the considerable energy release from the accretion disk of a BH? That's falling in, but not part of the BH yet, so can't be considered as BH radiation.

John

mugaliens
2008-Dec-08, 05:21 PM
...the amount of mass lost by Hawking Radiation (HR) is inversely proprotional the BH mass and the radius of the event horizon..

I keep seeing this - someone somewhere must have mistated it in a very public way. But it's not quite right.

The correct statement is that the time it takes a black hole to dissipate is proportional to the cube of it's mass. Since a black hole's mass is proportional to its radius, the dissipation time is also proportional to the cube of it's radius.

Thus, as the mass of a black hole increases, the rate of dissipation also increases, but, it does so disproportionately less than the mass. The result is that a black hole that's twice as massive will take eight times longer to dissipate.

On the flipside, when they have about 1 second left to go, they have a mass of 2.28E5 kg (half a million pounds) and an energy equivalence of 5 million megatons of TNT. That's 5 teratons, or 100,000 Tsar Bombas!

Quite a wallop for something that's nothing but a tiny speck...

grant hutchison
2008-Dec-08, 05:52 PM
Temperature is the thing that varies as inverse mass.

Grant Hutchison

galacsi
2008-Dec-08, 08:39 PM
Then from your previous posts, you imply that a black hole may lose mass by radiation.
Hawking got there before you, I fear, but the amount of mass lost by Hawking Radiation (HR) is inversely proprotional the BH mass and the radius of the event horizon. The bigger the BH, the less is lost, and the time for even a 'normal' BH (not a galaxy core one, nor a micro-BH) to decay by HR is more than the likely age of the Universe.

Are you thinking ogf the considerable energy release from the accretion disk of a BH? That's falling in, but not part of the BH yet, so can't be considered as BH radiation.

John

Not exactly. It is an ATM idea so I just want to answer you once and stop there.

I imply , if and it is a big if , that if light i.e EM energy has no gravitational impact then when the matter inside the black hole is transformed in energy then it ,the black hole ,see its gravity decreased. To push it to the max It could just for an instant reach gravity zero.
Anyway when gravity is small enough it explode or release EM and matter ,then behaving like a white hole. May be the two role can be enacted in the same time.
In this idea the black hole is not a true one it never reach the singularity.

it is kind of recycler or matter and energy.

But if what Mugaliens wrote is true my idea is just fantasy.

Galacsi.

JohnD
2008-Dec-09, 01:42 PM
mugaliens,
Thank you for the correction. Of course the factor that actually affects Hawking radiation is the deviation of the curvature of the event horizon from a flat plane. Or the radius of that curvature, that will vary as the cube of the mass. Hence duration of decay varies as the cube of the mass?
Thnaks to to Grant, for rigour as always.

galacsi,
I'm sorry - this fourm is like a barroom conversation, or if you like a debating society. If you ask a question, you cannot stipulate the nature of the answer!

I take it your question is directed at some SF concept, to further a story?
"if light i.e EM energy has no gravitational impact then when the matter inside the black hole is transformed in energy then it ,the black hole ,see its gravity decreased. To push it to the max It could just for an instant reach gravity zero."

As I said, Hawking got there first. Hawking radiation reduces the mass of the BH, and will do so to the point of the BH mass being zero, I presume when its diameter is less than one Plank length. It just takes a very long time to get there.
Once it has done so, there is nothing to drive the mass up again. So how could it "just for an instant reach gravity zero."?

If you wnat an answer, you must express your idea more clearly.
If you cannot, how can you expect your readers to appraciate it?

JOhn

grant hutchison
2008-Dec-09, 02:06 PM
Given that temperature varies with inverse mass, we can see how the lifetime dependency on mass cubed works out.

Radiant exitance (watts per square metre) varies with temperature to the power four, making it proportional to the inverse fourth power of mass. Surface area of the event horizon depends on radius squared, which is proportional to mass squared. The total power output of the black hole is radiant exitance times surface area, making power dependent on the inverse mass squared.

Rate of mass loss is proportional to power, via E=mc2. So the lifetime to complete evaporation is proportional to mass divided by power, or mass cubed.

Isn't dimensional analysis grand? :)

Grant Hutchison

JohnD
2008-Dec-09, 06:31 PM
Thanks, Grant, not the way I was thinking but MUCH more rigourous!
JOhn

mugaliens
2008-Dec-09, 06:56 PM
mugaliens,

Thank you for the correction.

Anytime - you've heard the best way to learn is by teaching...? I learn a lot, here!

Hence duration of decay varies as the cube of the mass?

...

Thnaks to to Grant, for rigour as always.

Exactly - and in that custom, he addressed your question about decay duration.

this fourm is like a barroom conversation, or if you like a debating society

More like a barroom brawl sometimes, but I like it, as we're among friends.

As I said, Hawking got there first. Hawking radiation reduces the mass of the BH, and will do so to the point of the BH mass being zero, I presume when its diameter is less than one Plank length. It just takes a very long time to get there.

Since the rate of radiation per unit of mass increase as the mass gets smaller, as time goes on, each moment in time sees a greater proportion of the BH's mass radiated away. As mentioned, 1 second before all of it has been radiated away, it still weighs 250 tons, all of which is converted to energy during that last second. The last Planck dimension is radiated away in Planck time or less.

Isn't dimensional analysis grand?

Grant Hutchison

It was almost an afterthought when I was in school. When a prof finally showed it to me, a lightbulb flickered to life, and it's been a good friend ever since (using dimensional analysis, not the light bulb).

galacsi
2008-Dec-09, 07:52 PM
galacsi,
I'm sorry - this fourm is like a barroom conversation, or if you like a debating society. If you ask a question, you cannot stipulate the nature of the answer!

Sorry if I gave this impression , but that was not my intention.

I take it your question is directed at some SF concept, to further a story?
Not at all , no bad novel in preparation !

If you wnat an answer, you must express your idea more clearly.
If you cannot, how can you expect your readers to appraciate it?

I don't know sir , may be the language barrier ? Let's try an other time :

I mean when matter is crushed inside the black hole , it is transformed in radiation. Then there is less and less matter as we know it and more and more EM energy inside. So the question was ; has EM energy a gravitational impact ? Because if it has not , the black hole having less and less matter inside see a decrease in its gravity. To the limit if at a given instant all matter is in the form of energy , it should have a null gravity.

Do you see the picture ? This is the motivation of my question about gravity of light.

JOhn[/QUOTE]

Hornblower
2008-Dec-09, 09:37 PM
I don't know sir , may be the language barrier ? Let's try an other time :

I mean when matter is crushed inside the black hole , it is transformed in radiation. Then there is less and less matter as we know it and more and more EM energy inside. So the question was ; has EM energy a gravitational impact ? Because if it has not , the black hole having less and less matter inside see a decrease in its gravity. To the limit if at a given instant all matter is in the form of energy , it should have a null gravity.

Do you see the picture ? This is the motivation of my question about gravity of light.

JOhnMy bold for reference. Yes, yes, a thousand times yes, if Einstein and his successors are right. It always has been my understanding that E = mc2, unconditionally. I do not expect the transformation of what we commonly call matter into another form of energy, while keeping it bottled up, to make its gravitational signature to go away.