Does a shadow have mass?

[Guest MacPhee]

phision, a shadow is the absence of something, a shadow can be made by almost anything, but the shadow it's self is the absence of what ever is making it not the presence of it. Photons, electrons, protons, magnetic fields, a positive or negative charge, atoms, dust, meteors, wind or even ocean waves can cast a shadow of sorts, to say a shadow has mass is some what misleading to say the least. It might be correct to say that a barrier to particles of some sort is needed to cast a shadow but they do not add mass to the shadow.

 

That's the point - there's no such "thing" as a shadow. As Boersun said in #32.

 

"Shadow" is only a word humans have invented. To describe what we see (or rather, don't see), when light gets blocked by something. When the light is blocked off, there's an absence of light. Which we call a "shadow" or "darkness". These words are just abstract nouns.

 

So to ask whether a "shadow" has mass, is like asking whether "darkness" has mass.

 

It's a meaningless question. (Or is it? Given the meaningless of modern theoretical Physics, could "Darkons" be the next fashionable idea after "Higgs" :( )

[phision]

Objects that have shadows have greater mass than identical objects that have no shadow! It seems obvious what that means!

[Moontanman]

Objects that have shadows have greater mass than identical objects that have no shadow! It seems obvious what that means!

 

 

Can you support that with some evidence?

[Aethelwulf]

I don't think there's such a thing as negative mass but that's what the absence of mass would be if it existed. Mathematically you could probably use imaginary mass but I doubt the results would have any meaning.

 

Back it up a second. Light does not have a mass.

[Aethelwulf]

That's the point - there's no such "thing" as a shadow. As Boersun said in #32.

 

"Shadow" is only a word humans have invented. To describe what we see (or rather, don't see), when light gets blocked by something. When the light is blocked off, there's an absence of light. Which we call a "shadow" or "darkness". These words are just abstract nouns.

 

So to ask whether a "shadow" has mass, is like asking whether "darkness" has mass.

 

It's a meaningless question. (Or is it? Given the meaningless of modern theoretical Physics, could "Darkons" be the next fashionable idea after "Higgs" :( )

 

 

I agree with what you said, but a shadow is not the absence of mass. Even when a shadow is the absence of photons, that shaded area always has matter in it. There is no such thing as empty space, nor is a shadow ''completely'' absent of photons.

[sunshaker]

Could a shadow be antiphotons, moving back in time causing an absense of light?

 

Plus shadows tend to be black and black is a mixture of certain colours.

photons and antiphotons are the same photons but have different properties at the quantum level, opposite values ie colour charge.

Edited November 26, 2012 by sunshaker

[CraigD]

Back it up a second. Light does not have a mass.

Though a physics purist would take me to task for the explanations that follow, according to best accepted theory, the photon has, and is experimentally shown to have, invariant mass zero, but this does not mean that light does not have mass.

 

When a single photon is emitted by an electron of an atom in one body and absorbed by an electron in an atom of another body, the mass of the emitting body decreases, and the mass of the absorbing body increases. A single photon passing an ordinary body, such as a planet, exerts a very gravitational force on it, slightly accelerating it. By nearly any practical definition, thus, an individual photon has a mass. The effective, or relativistic, mass of a photon is proportional to its frequency. (see this wikipedia section for more)

 

Because photons are bosons, they don’t follow Fermi-Dirac statistics, including the Pauli exclusion principle, so there is no limit to how closely photons can be “packed”, and thus no limit to the effective density of a volume of space containing them. An extreme consequence of this is that it’s theoretically possible to make a black hole out of photons only, a never-observed or predicted object known as a kugelblitz.

 

Since relativistic mass can be considered invariant mass times Lorentz factor ([math]\left(1 - \left(\frac{v}{c}\right)^2 \right)^{-\frac12}[/math]), I like to whimsically consider the well defined, finite relativistic mass of a photon to be an example of multiplying zero and infinity to get a finite number. :)

[CraigD]

Could a shadow be antiphotons, moving back in time causing an absense of light?

Not by any physics of which I’ve ever heard!

 

Per best accepted present day theory, and any I can imagine, the photon is its own antiparticle, so there simply is no such thing as an antiphoton.

 

Plus shadows tend to be black and black is a mixture of certain colours.

photons and antiphotons are the same photons but have different properties at the quantum level, opposite values ie colour charge.

Can you back up these bizarre claims with links or references? I’m nearly certain you cannot!

 

Your paragraph appears a litany of classical art and modern physics misconceptions, sunshaker! Light of many colors are perceived by human and other animal eyes and brains as the color white. The absence of visible light is perceived as the color black. As noted above, there’s no such thing as an antiphoton. In QCD, color charge is a property of quarks and gluons related to their strong interaction, in no way related to visible color, but rather, along with red, green, and blue, convenient terms to use for a three-kind property.

[phision]

Can you support that with some evidence?

I shall try...

 

When a single photon is emitted by an electron of an atom in one body and absorbed by an electron in an atom of another body, the mass of the emitting body decreases, and the mass of the absorbing body increases. A single photon passing an ordinary body, such as a planet, exerts a very gravitational force on it, slightly accelerating it. By nearly any practical definition, thus, an individual photon has a mass. The effective, or relativistic, mass of a photon is proportional to its frequency. (see this wikipedia section for more)

 

CraigD's post seems to fly in the face of your earlier post...

Some shadows are not generated by blocking but by bending the particles around the object, how does this figure into your idea? Photons impacting an object would not add mass to it , I think your idea of shadows having mass is busted.

 

and lend credence to my earlier post!

objects that have shadows, have greater mass, as they are being struck by, energy waves or partical streams. shadows indicate mass being added to the shading element! the mass being added, is the mass of the shadow. equal to mass~energy of the waves/particals being blocked.

 

So CraigD's post quoted above and the meaning of shadow, in post #26, as, "cast... by a body intercepting light.", it follows that post#36 seems to be factually accurate.

[Aethelwulf]

Could a shadow be antiphotons, moving back in time causing an absense of light?

 

Plus shadows tend to be black and black is a mixture of certain colours.

photons and antiphotons are the same photons but have different properties at the quantum level, opposite values ie colour charge.

 

 

No, because photons are their own antiparticles.

[Aethelwulf]

Though a physics purist would take me to task for the explanations that follow, according to best accepted theory, the photon has, and is experimentally shown to have, invariant mass zero, but this does not mean that light does not have mass.

 

When a single photon is emitted by an electron of an atom in one body and absorbed by an electron in an atom of another body, the mass of the emitting body decreases, and the mass of the absorbing body increases.

 

Yes... there are two main reasons however we don't tend to think a photon has a mass - well actually three.

 

The first comes from gauge invariance. Photons are well tested that they are actually massless and fits well into gauge theory when charge conservation is considered. The second reason is that if the photon did have a mass, it would be ridiculously small, something like [math]10^{-51}kg[/math]. The third reason is because of special relativity and how it treats mass moving at the speed of light. Taking into account that [math]\beta = \frac{v}{c}[/math], we know there is a fundamental speed limit on systems with mass using [math]\gamma^{-2} = \sqrt{1 - \beta^2}[/math]. Correcting velocities up to the speed of light one will find that a system requires an infinite amount of energy just to try and reach the value of the speed of light. So if the photon did actually have a mass, it's mass would be infinite.

Edited November 27, 2012 by Aethelwulf

[Aethelwulf]

ow Fermi-Dirac statistics, including the Pauli exclusion principle, so there is no limit to how closely photons can be “packed”, and thus no limit to the effective density of a volume of space containing them. An extreme consequence of this is that it’s theoretically possible to make a black hole out of photons only, a never-observed or predicted object known as a kugelblitz.

 

 

 

Sure, yes, energy can make matter no doubt about it. Have enough photon energy and you can make particles and antiparticles.

[Aethelwulf]

You know, you might also hear people tell you that matter is a property of energy. This statement isn't exactly correct.

 

http://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence

 

''In physics, in particular special and general relativity, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. In this concept, mass is a property of all energy, and energy is a property of all mass, and the two properties are connected by a constant.''

 

 

It is true that energy and matter are simply different forms of each other, but not all systems made from energy has a property of mass. [math]E=Mc^2[/math] is a non-relativistic formula, it does not work for particles of photons. [math]E=Mc^2[/math] is an approximation for slow moving systems. Photons are demonstrated from

 

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

 

Since their mass is zero then

 

[math]E^2 = p^2c^2[/math]

 

which can reduce to simply

 

[math]E = pc[/math] for a photon. So even the wiki article after me looking at it does not explain it very well. A photon adds mass to system because it contributes to the overall energy of the system. Energy is related to inertia in this sense, ''giving mass'' to a system by increasing it's energy content, keeping in mind inertia and mass are the same thing in relativity through the weak equivalence principle.

Edited November 27, 2012 by Aethelwulf

[Aethelwulf]

As I said, they are two forms of each other, matter and energy. Matter is in fact just a concentrated form of energy, whilst energy is in fact a diffused form of matter.

[Urod]

Dear Group,

 

I know it sounds like a foolish question but ..... is really a discussion about the mass of shadows.

 

We can see shadows, we can measure their area, observe their outlines..but we cannot 'weigh' a shadow, as shadows are illusions of light that have no mass ...

 

 

 

You are good ! It's so easy to atract attention with a good title .

 

Since 'shadow' is only a Name to designate the phenomenon of opaque bodies obstructing light , shadows are abstract hence non-material therefore they do not physically exist .

Hence the tricky question of the thread is " Does something that does not exist has mass ? " . :) And people did respond plus over 10,000 views !!!

 

And so the Anonymous Tester had its proof ... Good job !

 

 

But here is a bonus : the previous poster ' Aethelwulf ' said :

 

" E>2 = p>2 c>2 // >2 is Squared , didn't copy/paste properly from above reply .

 

which can reduce to simply

 

E = pc

 

for a photon. " , end quote .

 

This is a typical example of manipulating Math without taking in consideration the Physics behind it .

E Squared it is NOT the same as E , threfore the first formula whith Squared members it is NOT the same as the formula with the non-squared members !! It's so obvious ! Higher energy Physics are NOT the same as lower energy phenomenon , no ???

 

 

 

And last , for posterity , the thread questioning if nothing has mass was accepted in the Astronomy/Cosmology while my UPN proving logically what Volovik and Huang proved with formulas , a SuperFluid Universe , is still in the Crazy section !

Edited November 27, 2012 by Urod

[LaurieAG]

Mirror matter-type dark matter was covered in a paper by Robert Foot in 2004.

 

http://arxiv.org/abs/astro-ph/0407623

 

The purpose of this article is to provide an up-to-date and pedagogical review of this dark matter candidate.

 

And Charles Dodgson covered a similar area in 1871.

 

http://en.wikipedia.org/wiki/Through_the_Looking-Glass

 

Alice is playing with a white kitten (whom she calls "Snowdrop") and a black kitten (whom she calls "Kitty")—the offspring of Dinah, Alice's cat in Alice's Adventures in Wonderland—when she ponders what the world is like on the other side of a mirror's reflection. Climbing up on the fireplace mantel, she pokes at the wall-hung mirror behind the fireplace and discovers, to her surprise, that she is able to step through it to an alternative world. In this reflected version of her own house, she finds a book with looking-glass poetry, "Jabberwocky", whose reversed printing she can read only by holding it up to the mirror.

 

At least Charles Dodgsons stories go from and return back to reality at the end.

[Aethelwulf]

 

But here is a bonus : the previous poster ' Aethelwulf ' said :

 

" E>2 = p>2 c>2 // >2 is Squared , didn't copy/paste properly from above reply .

 

which can reduce to simply

 

E = pc

 

for a photon. " , end quote .

 

This is a typical example of manipulating Math without taking in consideration the Physics behind it .

E Squared it is NOT the same as E , threfore the first formula whith Squared members it is NOT the same as the formula with the non-squared members !! It's so obvious ! Higher energy Physics are NOT the same as lower energy phenomenon , no ???

 

 

 

Actually, there is a lot of physics behind it, even though it is pure math.

 

It is true we had

 

[math]E^2= p^2c^2[/math]

 

I said this can reduce to

 

[math]E = pc[/math]

 

Instead of saying

 

[math]E = \sqrt{p^2c^2}[/math]

 

the reason why we can reduce it to

 

[math]E = pc[/math]

 

Is because there is no such thing as a negative momentum. Pure physics without superfluous mathematics.

Edited November 28, 2012 by Aethelwulf