light has inertia?

[Sedit]

[math]E^2 = m^2c^4 + p^2c^2[/math]

 

^{[math]E = mc^2[/math]} assumes a particle at rest.

 

rodger that load and clear captian thank you

 

Has anyone ever tryed an experiment to test for weight change in a system that absorbes photons or materials that light moves slower in?

[Tom Vose]

The weight of a photon, or the mass rather, lies between 10^50 and 10^51. If it has a mass that is.

 

It might have a mass, and if it does, it will have a weight, and if it has a weight, one of Einsteins propositions will be shown wrong.

[swansont]

rodger that load and clear captian thank you

 

Has anyone ever tryed an experiment to test for weight change in a system that absorbes photons or materials that light moves slower in?

 

Yes. An isomer (long-lived excited state) of iron was discovered because its mass is different than the ground state.

 

http://blogs.scienceforums.net/swansont/archives/278

[D H]

The weight of a photon, or the mass rather, lies between 10^50 and 10^51. If it has a mass that is.

That doesn't make sense since you didn't specify units. It makes even less sense with units. It makes even less sense as you specified a range for the photon mass.

 

A rest mass of zero is within experimental error in every experiment to date to assess the mass of a photon. The experimentally ascertained upper limit on the photon mass is dropping as experimental techniques improve.

 

You are probably referring to experiments by Jun Luo and his associates, described in http://www.aip.org/pnu/2003/split/625-2.html

A new limit on photon mass, less than 10

^-51

grams or 7 x 10

^-19

electron volts, has been established by an experiment in which light is aimed at a sensitive torsion balance; if light had mass, the rotating balance would suffer an additional tiny torque.

 

Note the difference. The report specifies a number along with units, and specifies that the result is an upper limit. The lower limit is zero.

 

 

It might have a mass, and if it does, it will have a weight, and if it has a weight, one of Einsteins propositions will be shown wrong.

Careful, now. There are three distinct meanings of the word "weight".

1. Legally and colloquially, weight is a synonym for mass and has units of mass. In this sense, yes, if a photon has mass it has weight.
   
2. In pre-university and some lower level university classes, and to airplane designers, weight is gravitational acceleration times mass (units of force). This is not a very useful definition as there is no way to measure this definition of weight. In this sense, if a photon has mass, it has weight, but only if it is under the influence of an (observable) gravitational field.
   
3. In some undergraduate physics classes and almost all general relativity classes, weight is what an ideal spring scale weighs. In classical physics, this is the net non-gravitational force acting on an object; in general relativity, this is the net force acting on an object (gravity is a pseudo-force and doesn't count). Even if a photon does have mass, it has no weight per this definition. As soon as something acts on a photon it ceases to exist.

Bottom line: Scrape the idea of weight. If a photon has non-zero mass there are a whole lot of things in physics that need to be patched up.

[Severian]

The weight of a photon, or the mass rather, lies between 10^50 and 10^51. If it has a mass that is.

 

Where do these crackpots come from? What attracts them to science? Do you think they really believe the things they say (is it a mental health problem)? Or are they just deliberately trying to mislead and confuse?

[Tom Vose]

Where do these crackpots come from? What attracts them to science? Do you think they really believe the things they say (is it a mental health problem)? Or are they just deliberately trying to mislead and confuse?

 

You little shit.

 

Oh and DH, you want me to reply, don't worry. You want me define, a subject which seems so carelessly defined as it is...

 

That doesn't make sense since you didn't specify units. It makes even less sense with units. It makes even less sense as you specified a range for the photon mass.

 

A rest mass of zero is within experimental error in every experiment to date to assess the mass of a photon. The experimentally ascertained upper limit on the photon mass is dropping as experimental techniques improve.

 

You are probably referring to experiments by Jun Luo and his associates, described in http://www.aip.org/pnu/2003/split/625-2.html

A new limit on photon mass, less than 10

^-51

grams or 7 x 10

^-19

electron volts, has been established by an experiment in which light is aimed at a sensitive torsion balance; if light had mass, the rotating balance would suffer an additional tiny torque.

 

Note the difference. The report specifies a number along with units, and specifies that the result is an upper limit. The lower limit is zero.

 

 

 

Careful, now. There are three distinct meanings of the word "weight".

1. Legally and colloquially, weight is a synonym for mass and has units of mass. In this sense, yes, if a photon has mass it has weight.
   
2. In pre-university and some lower level university classes, and to airplane designers, weight is gravitational acceleration times mass (units of force). This is not a very useful definition as there is no way to measure this definition of weight. In this sense, if a photon has mass, it has weight, but only if it is under the influence of an (observable) gravitational field.
   
3. In some undergraduate physics classes and almost all general relativity classes, weight is what an ideal spring scale weighs. In classical physics, this is the net non-gravitational force acting on an object; in general relativity, this is the net force acting on an object (gravity is a pseudo-force and doesn't count). Even if a photon does have mass, it has no weight per this definition. As soon as something acts on a photon it ceases to exist.

Bottom line: Scrape the idea of weight. If a photon has non-zero mass there are a whole lot of things in physics that need to be patched up.

 

What units? These units by any chance..?

 

W=gm...

 

Which would be m=w/g?

 

 

As for the rest, for what i have read... ''yes''.

 

Oh right... the units... i missed them concerning the lower mass of the photon...

 

 

, here, what units do you think they have? (Just out of interest).. I DEFINE it as grams

Edited December 17, 2008 by Tom Vose
multiple post merged

[Severian]

If light has mass, how do you explain the inverse square law of electromagnetism?

 

(We have had this discussion before, by the way. So you might find a quick search helps you answer that one.)

[D H]

You little shit.

No need for that. Severian replied the way he did because, based on the post both he and I quoted, you gave every appearance of being a crackpot (of which we have more than our fair share at this site and at this time of year). Specifically,

• You specified a range for the photon mass which excludes zero. That made it appear that you think photons have a non-zero mass. That photons having a non-zero rest mass is one of the more common crackpot conjectures. How you use words is important.
  
• You specified a mass without specifying units. Crackpots are notoriously sloppy with units.
  
• You missed a negative sign on the exponent, assuming you meant grams. Crackpots are notoriously bad with scientific notation.

 

Some advice: Stop being so flip, take the chip off your shoulder, and please a bit more careful in what you say.

[Sedit]

ok here is me trying not to sound like a crack pot my self

 

But my question is light has momentum correct

which is a measure of g-cm/sec

 

and that momentum can be imparted on contact with and object

(like the radiometer bulbs <- if i got that name right(and the principle for that matter))

 

but since something increases in mass as it approches the speed of light wouldnt that make the already apprently small amount of mass that may be present in a photon a very small fraction of the moment of inertia that is being measured all ready?

 

Also wouldnt that seem to state that like everyday mass wouldnt the amount of energy to go the speed of light be infinite?

 

The about questions is what happends when a laymen tryed to teach himself science since he was little. The classic laws get butcherd:D

[swansont]

but since something increases in mass as it approches the speed of light wouldnt that make the already apprently small amount of mass that may be present in a photon a very small fraction of the moment of inertia that is being measured all ready?

 

Post #24. Mass doesn't change with speed; all of that energy shows up in the kinetic term, p^2c^2

[Tom Vose]

I never said light had inertia. I said that if light [[had]] a mass..

 

And by the way, a moving object has more mass than a stationary object, so yes, mass does change with speed.

 

No need for that. Severian replied the way he did because, based on the post both he and I quoted, you gave every appearance of being a crackpot (of which we have more than our fair share at this site and at this time of year). Specifically,

• You specified a range for the photon mass which excludes zero. That made it appear that you think photons have a non-zero mass. That photons having a non-zero rest mass is one of the more common crackpot conjectures. How you use words is important.
  
• You specified a mass without specifying units. Crackpots are notoriously sloppy with units.
  
• You missed a negative sign on the exponent, assuming you meant grams. Crackpots are notoriously bad with scientific notation.

 

Some advice: Stop being so flip, take the chip off your shoulder, and please a bit more careful in what you say.

I am not a crackpot. I take science very seriously, and i know all the units before you make any conjectures on my ability to talk about science. It just so happens i missed it out, nothing more nothing less.

[ajb]

I never said light had inertia. I said that if light [[had]] a mass..

 

And by the way, a moving object has more mass than a stationary object, so yes, mass does change with speed.

 

 

I am not a crackpot. I take science very seriously, and i know all the units before you make any conjectures on my ability to talk about science. It just so happens i missed it out, nothing more nothing less.

 

 

Why does this keep coming up? There must be several threads on the topic of mass in special relativity.

 

Mass does not change with speed.

 

Severian has good credentials.

[Tom Vose]

Why does this keep coming up? There must be several threads on the topic of mass in special relativity.

 

Mass does not change with speed.

 

Severian has good credentials.

 

 

Explain then, because as far as i was taught, a stationary object has less mass than a moving object.

[swansont]

[math]E^2 = m^2c^4 + p^2c^2[/math]

 

The energy changes when an object is moving. The mass doesn't.

[D H]

And by the way, a moving object has more mass than a stationary object, so yes, mass does change with speed.

Relativistic mass changes with speed. Invariant mass (aka rest mass) does not. One can use relativity without invoking the concept of relativistic mass; it is merely a synonym for energy ([math]m=E/c^2[/math]) and is a completely unnecessary appendage (use energy instead). Invariant mass on the other hand is an essential characteristic of an object. When one talks about a photon having zero mass, the term obviously means invariant mass. Most physicists use the term "mass" without qualification to refer to invariant mass. When they do mean relativistic mass they generally say "relativistic mass".

 

Note: A photon does have non-zero relativistic mass given by [math]m=h\nu/c^2[/math], which results directly from the Planck relation and the relativistic mass–energy equivalence formula.

[Tom Vose]

That is the most trivial thing ever, for, a relativistic mass system does not have mass. This much must be clear that i was not talking about a pure energy system.

 

Again, i repeat, a system that moves has more mass than a stationary system. And no, one does not speak of a non-mass system here, for how can one?

 

Super trivial.

[D H]

Again, i repeat, a system that moves has more mass than a stationary system.

Again, I repeat, it does not. The invariant mass is invariant. The term mass usually refers to invariant mass, not relativistic mass.

 

You are being sloppy with words. For a particle with non-zero invariant mass, its relativistic mass of a particle, which does vary with velocity, is

 

[math]m_{\text{rel}} = m_0 \frac 1 {\sqrt{1+(v/c)^2}} = \frac E{c^2}[/math]

 

Note the [math]m_0[/math] in the above. That is the invariant mass (rest mass), and that quantity does not vary with speed. Hence the name, invariant mass. In the special case that the velocity is zero, the relativistic mass is equal to the invariant mass. Hence the alternate name for invariant mass, rest mass.

[Tom Vose]

yes, M=F/a does not necesserily change, under this math. However, it can with a change in momentum.

 

The relativistic mass changes, i agree. Would this solve this arguement?

[Klaynos]

That is the most trivial thing ever,

 

Not really, as it can cause significant confusion. Which is why I dislike the use of relativistic mass, especially when teaching people.

[Reaper]

I was WAY too caught up in classical thinking. The equations didn't help much (only they did make me realize that it's just they way nature behaves, and the equations describe nature, and the equations tell us that photons have momentum)... I was looking for something more intuitive.

 

[emphasis mine]

 

I guess that was the root of your problem then. Intuition counts for zilch in physics, and mathematics for that matter.

[iNow]

Yeah, and it sure didn't help that my basis for understanding momentum was based on a misconception.

[ajb]

Explain then, because as far as i was taught, a stationary object has less mass than a moving object.

 

I think other people here have explained it ok. Well, for sure well enough for now.

 

 

Note: A photon does have non-zero relativistic mass given by [math]m=h\nu/c^2[/math], which results directly from the Planck relation and the relativistic mass–energy equivalence formula.

 

Not sure I would quite say that. Really you mean it has momentum.

[Tom Vose]

Ajb, yes, i thought it was universally-known that the relativistic mass changes. It's just that i did not specify that, as i thought i didn't need to.

[swansont]

Ajb, yes, i thought it was universally-known that the relativistic mass changes. It's just that i did not specify that, as i thought i didn't need to.

 

On the contrary, mass is generally taken to mean invariant mass. You need to specify relativistic mass if you are going to use it.

[ajb]

I am with swansont on this one. Very rarely will anyone use mass to mean anything other than "invariant" mass, the "thing in the mass-shell condition".