Can Concentrated Light Create Gravity by Warping Space-Time?

[anantchowdhary]

Light is energy.Also light has photons as energy carriers.So,if large amount of light is concentrated on a small area to an extent that the energy has effect of significantly large mass,would it create gravity as energy also warps space-time?

 

[Hootenanny]

Yes, photons do produce curvature in space-time. As you correctly say, energy curves space-time. However, as I have said in previous threads I strongly disagree that photons have 'mass' so much in as I strongly disagree with the use of 'relativistic mass' which is not real. So I would prefer if we do not discuss that photons 'in effect' have mass.

 

[disregardthat]

No, at least not the way I see it. The photon have 0 mass, and there is no number you can muliply it with to get more than 0.
Anyway, the 'evidense' that the photon has zero mass, is because it moves at einsteins constant 'c', I think.

 

[anantchowdhary]

Hmm.Mass and energy have the same effects if I am not mistaken!

 

[disregardthat]

This makes me confused, if energy equals mass, how can zero mass be energy at all :S. the photon have energy all right, but I thought it was in a 'preserved medium' that it didn't have any mass. Guess it was wrong...

 

[anantchowdhary]

Sorry.Mass is a form of energy.When mass energy is converted to any other form of energy E=mc^2 can be useful in calculating only the AMOUNT of energy.A photon has effects of mass as it caries energy

 

[anantchowdhary]

@Hootenanny

Why do forms of energy differ at all?

 

[Hootenanny]

Jarle: What is a preserved medium?

To all: This is why I dislike the use of relativistic mass, it only results in confusion.

 

[Hootenanny]

Why do forms of energy differ at all?

They differ in the way they are defined. For example gravitational potential energy is defined as the potential energy per unit mass of an object in a gravitational field. Thermal energy is defined as internal energy of a system.

 

[cristo]

I agree with Hootenanny: using the relativistic mass leads to confusion. The relativistic mass is not "real" in the sense that, with the correct choice of inertial frame, the relativisitic mass of a particle will be zero.

However, the mass of a particle is invariant under transformations between inertial frames, and thus this is a "real" quantity.

 

[anantchowdhary]

Then why are their effects different in nature?

 

[Hootenanny]

Then why are their effects different in nature?

What do you mean by 'their effects'?

 

[ranger]

Guys as I've come to realize, thanks to hootenanny, its better to speak of momentum and energy as it relates to velocity rather than "how mass increases". Introducing relativistic mass will only add confusion.

http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html

 

[anantchowdhary]

heat energy has the heating effect,electrical energy causes motion of electrons.Why isn't it say,the other way round?

 

[cristo]

@Hootenanny

Why do forms of energy differ at all?

Anantchowdhary: I recall a few days ago, you asking the same question, to which russ_waters replied and gave you a link to a site describing different forms of energies. Here is the link to that thread: https://www.physicsforums.com/showthread.php?t=150002
Did you read the webpage?

 

[anantchowdhary]

Yea surely i did as the thread was made by me.But still i haven't got any clear answer.Zap was wrong as what he was trying to say was lik saying if u stack up shoes ull get a house.That was not what i meant

 

[ranger]

heat energy has the heating effect,electrical energy causes motion of electrons.Why isn't it say,the other way round?

Electrical energy doesn't bring about the motion of electrons, rather its the energy made available by the flow of electric charge in a conductor.

 

[Hootenanny]

Then what do you mean, because I for one am pretty confused as to what you're asking if that previous thread didn't answer your question.

 

[anantchowdhary]

I read the thread as i made it.But still I've got no clear answer

 

[cristo]

Yea surely i did as the thread was made by me.But still i haven't got any clear answer.Zap was wrong as what he was trying to say was lik saying if u stack up shoes ull get a house.That was not what i meant

With all due respect, I suggest you read up on the fundamentals of energy. Then come back with a specific question with respect to a point that you are not clear on, since, at present, you are just waffling!

 

[notknowing]

Yes, photons do produce curvature in space-time. As you correctly say, energy curves space-time. However, as I have said in previous threads I strongly disagree that photons have 'mass' so much in as I strongly disagree with the use of 'relativistic mass' which is not real. So I would prefer if we do not discuss that photons 'in effect' have mass.

It seems that a lot of people get quit emotional about relativistic mass . The concept of relativistic mass is a DEFINITION which can be looked up in many books, so the concept is real enough (even if some dislike it).

Consider however the following thought experiment. Take a box with perfect mirrors on the inside and weigh the box on a very precise balance (for instance at the surface of the earth). Then, inject a large number of photons into this box (which continue bouncing inside the box since we have assumed perfect mirrors). I'm very sure that the photon-filled box will weigh now more then the empty box. This proves that photons have mass (while the invariant mass is of course zero).

 

[Chris Hillman]

Say "kinetic energy", not "relativistic mass"

The concept of relativistic mass is a DEFINITION which can be looked up in many books, so the concept is real enough (even if some dislike it).

This is just a (very misleading) synonym for kinetic energy (in relativistic kinematics).

I'm very sure that the photon-filled box will weigh now more then the empty box. This proves that photons have mass (while the invariant mass is of course zero).

Photons do not have mass. But they carry energy, which gravitates.

Here's an easier conundrum: suppose you have an isolated object in deep space and you someone heat it up. Does it now have a larger gravitational mass?

 

[Littlepig]

Here's an easier conundrum: suppose you have an isolated object in deep space and you someone heat it up. Does it now have a larger gravitational mass?[/QUOTE]

larger gravitacional mass don't think so. but who am I? but what happens to its spacetime curvature?? increases?

 

[Hootenanny]

Chris Hillman has answered the technical points of your post, so I won't repeat what has already been said. However, I would still like to comment on something

It seems that a lot of people get quit emotional about relativistic mass . The concept of relativistic mass is a DEFINITION which can be looked up in many books, so the concept is real enough (even if some dislike it).

True, I do disagree with the notion of relativistic mass (as Einstein*), since the actual definition, is somewhat misleading and as Chris Hillman said, it is much better to consider it kinetic energy in SR. However, another reason I disagree with its use is that it usually only serves to complicate problems (especially conceptual ones), as this thread exemplifies. For example, a common 'definition' of 'relativistic mass' is, as I'm sure you know;

m=\gamma m_{0} = \frac{m_{0}}{\sqrt{1-\beta}}

Using this definition, how can you claim that a photon has relativistic mass?

\hline[/itex]<br /> *And before the replies come flying in, no I am not comparing myself to Einstein.

 

[jtbell]

I'm very sure that the photon-filled box will weigh now more then the empty box. This proves that photons have mass (while the invariant mass is of course zero).

Only if you require that mass be an additive quantity.

 

[pervect]

Only if you require that mass be an additive quantity.

Let me expand on this a bit.

Relativistic mass, being usually defined as a synonym for energy, is an additive quantity in special relativity - one finds the total energy of a system by adding together the sum of the energies of the part. However, the relativistic mass of a system is not independent of the observer.

The invariant mass of a system in special relativity is not an additive quantity. One finds the total energy of a system, E, by addition, and also the total momentum, P, of the system by addition. One then computes the invariant mass from these two quantities (the energy, E, and the magnitude of the total momentum vector).

While it is apparently more complicated to compute the invariant mass of a system, it has the very useful property that it is independent of the obsever - at least for isolated systems.

Philosphies vary, but I for one view observer indpendent quantites as easier to work with and "more fundamental" than observer dependent quantities. So just as the Lorentz interval is observer independent while distance is not, invariant mass is observer independent while relativistic mass is not.

 

[Jimmini]

Light is energy.Also light has photons as energy carriers.So,if large amount of light is concentrated on a small area to an extent that the energy has effect of significantly large mass,would it create gravity as energy also warps space-time?

I have upset people over mentioning that about all equations of potential or force as they require mass. Including h/mc.
Einstein has postulated that any energy has its' own gravitational effect.
It is possible because of his e=mc^2 idea. If a mass travels at linear velocity c, where does the angular potential come from ? It's equal gravitational effect ? Or, as mass has velocity, it has a gravitational effect equal to its' linear potential which is considered as angular potential ?

 

[pervect]

Here's an easier conundrum: suppose you have an isolated object in deep space and you someone heat it up. Does it now have a larger gravitational mass?

larger gravitacional mass don't think so. but who am I? but what happens to its spacetime curvature?? increases?

Heat and/or kinetic energy does contribute to the mass of a system. Thus the correct answer to the above question is that heating up a body does increase its mass. In GR, "gravitational mass" is actually rather redundant - because of the equivalence principle there is only one sort of mass.

The best reference I know of is http://arxiv.org/abs/gr-qc/9909014, while the paper itself is quite technical, the abstract of the paper is pretty clear on this point:

According to the general theory of relativity, kinetic energy contributes to gravitational mass. Surprisingly, the observational evidence for this prediction does not seem to be discussed in the literature. I reanalyze existing experimental data to test the equivalence principle for the kinetic energy of atomic electrons, and show that fairly strong limits on possible violations can be obtained. I discuss the relationship of this result to the occasional claim that ``light falls with twice the acceleration of ordinary matter.''

In special relativity, this should be clear from the defintion of mass (invariant mass).

The invariant mass of the system is proportional to sqrt(E^2 - p^2). In many cases it is convenient to study a system in a frame where the total momentum of the system is zero. In this case, m = E/c^2 as per Einstein's famous equation, so that increasing the energy of a system by increasing its temperature should obviously increase its mass.

 

[Rudi Van Nieuwe]

Chris Hillman has answered the technical points of your post, so I won't repeat what has already been said. However, I would still like to comment on something

True, I do disagree with the notion of relativistic mass (as Einstein*), since the actual definition, is somewhat misleading and as Chris Hillman said, it is much better to consider it kinetic energy in SR. However, another reason I disagree with its use is that it usually only serves to complicate problems (especially conceptual ones), as this thread exemplifies. For example, a common 'definition' of 'relativistic mass' is, as I'm sure you know;

m=\gamma m_{0} = \frac{m_{0}}{\sqrt{1-\beta}}

Using this definition, how can you claim that a photon has relativistic mass?

\hline[/itex]<br /> *And before the replies come flying in, no I am not comparing myself to Einstein.

<br /> You are not using the correct definition of relativistic mass. The relativistic mass is defined by dividing its (total) energy by c^2 (see <a href="http://en.wikipedia.org/wiki/Relativistic_mass" target="_blank" class="link link--external" rel="nofollow ugc noopener">http://en.wikipedia.org/wiki/Relativistic_mass</a> ). So, if you divide the energy of the photon (given by h * frequency) by c^2, you obtain its relativistic mass.

 

[Rudi Van Nieuwe]

This is just a (very misleading) synonym for kinetic energy (in relativistic kinematics).

No, the relativsitic mass correspond to the rest mass PLUS the kinetic energy (converted to mass). I also do not understand why this is misleading.

Photons do not have mass. But they carry energy, which gravitates.

Since when is E not anymore equal to M c^2 ? If photons have energy (which is 100 % sure), then they also have (relativistic) mass.

 

[Hootenanny]

This thread began with the question "Do photons curve space-time?" (or something to that effect). Let us not turn this into a discussion of Invariant vs. Relativistic mass.

 

[anantchowdhary]

So finally is it possible to create a black hole in an arbit situation with the use of just light?

 

[ranger]

So finally is it possible to create a black hole in an arbit situation with the use of just light?

Read this:
http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_fast.html

You should think of a black hole as mass concentrated into a signle point rather than your orbit situation.

 

[Chris Hillman]

Vaidya thought experiments

Hi, anantchowdhary,

So finally is it possible to create a black hole in an arbit situation with the use of just light?

Let me rephrase your question: electromagnetic radiation with random polarizations can be treated in gtr as a "null dust". So, is it possible to create a black hole using only the energy contained in a collapsing spherical shell of null dust?

The answer is "yes", as can be seen from the Vaidya null dust, an exact null dust solution which generalizes the Schwarzschild vacuum. In fact, it is well worth studying some scenarios in detail since you can learn much about black holes this way. In particular, we can clearly see the "teleological" nature of the event horizon. See Frolov & Novikov, Black Hole Physics, Kluwer.

 

[SF]

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