Is light heavy

[Deverebond]

My question is, is light heavy. Ive tried asking in other forums but don't get any good answers.

I've been told photons are massless but have momentum (a product of mass and velocity) so that doesn't make sense.

Matter is transformed into energy so if there is light in the universe is it getting less massive. If yes what runs out first energy or matter?

[Mordred]

The answer you should have gotten is light has no rest (invariant mass) but has relativistic (inertial mass). via

 

[latex] e^2=pc^2+(m_oc^2)^2 [/latex]

 

Matter is irrelevant in the case of photons as it is a boson and only fermions count as matter.

 

The total particle count in the universe maintains at roughly 10^90 particles. Your question on which runs out first has little meaning as all particles have decay rates (though some have incredibly long decay rates ie longer than the age of the universe) so particles do regularly change into other particles provided the decay follows numerous conservation rules

Edited April 27, 2017 by Mordred

[Bender]

As far as I know, protons and electrons have never been observed to decay, so we don't know whether they have a decay rate.

Edited April 27, 2017 by Bender

[Mordred]

As far as I know, protons and electrons have never been observed to decay, so we don't know whether they have a decay rate.

They are still theorized to have a decay rate. Just so incredibly long that we will never observe them decay. Though the electron afiak can't decay further as there is no particle of less mass that it can decay into.

https://en.m.wikipedia.org/wiki/Proton_decay

 

However there is research into electron decay even then

 

https://arxiv.org/abs/hep-th/0312325

Edited April 27, 2017 by Mordred

[Strange]

I've been told photons are massless but have momentum (a product of mass and velocity) so that doesn't make sense.

 

 

Momentum is only the product of mass and velocity for particles with mass. It is just an intrinsic property of photons.

[Sriman Dutta]

momentum of photons = hf/c, f is the frequency, c is the speed of light and h is Planck's constant.

[mistermack]

I have to say that light IS heavy. If you define heavy as something that responds to gravity.

 

In a black hole, photons are too heavy to escape.

[swansont]

I have to say that light IS heavy. If you define heavy as something that responds to gravity.

 

 

 

Which is not the definition.

[mistermack]

Which is not the definition.

But what's the official definition?

 

Wikipedia says "In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co-exist and find use in their various contexts.^[2]"

 

If an apple is hanging from a tree, it's heavy. If it's in free fall, it's weightless. So it depends what it's doing.

 

I remember reading somewhere that if you trapped a photon between two perfect mirrors, the system gains rest mass, until the photon escapes. In inertial motion through curved space, the photon would be weightless and in free fall, but so would the apple.

[swansont]

But what's the official definition?

 

Wikipedia says "In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co-exist and find use in their various contexts.^[2]"

 

If an apple is hanging from a tree, it's heavy. If it's in free fall, it's weightless. So it depends what it's doing.

 

I remember reading somewhere that if you trapped a photon between two perfect mirrors, the system gains rest mass, until the photon escapes. In inertial motion through curved space, the photon would be weightless and in free fall, but so would the apple.

 

 

Photons have no mass. They do not have to be traveling on a null geodesic for that to happen.

 

Using your definition, an electron is heavy, since it responds to gravity. All things would be heavy, according to you, which makes the definition useless.

[mistermack]

 

 

Photons have no mass. They do not have to be traveling on a null geodesic for that to happen.

 

Using your definition, an electron is heavy, since it responds to gravity. All things would be heavy, according to you, which makes the definition useless.

A definition is of use, if it more clearly explains what people mean, by a certain word or expression.

And that can vary depending on who's talking, and the context. Hence the debate about defining weight.

 

Do gravitons respond to gravity?

[Silvestru]

A definition is of use, if it more clearly explains what people mean, by a certain word or expression.

And that can vary depending on who's talking, and the context. Hence the debate about defining weight.

 

Do gravitons respond to gravity?

 

Gravitons, if proved to exist have no mass. So we go back to what SwansonT said

[swansont]

A definition is of use, if it more clearly explains what people mean, by a certain word or expression.

And that can vary depending on who's talking, and the context. Hence the debate about defining weight.

 

The word under scrutiny is "heavy"

[mistermack]

 

The word under scrutiny is "heavy"

According to Wikipedia, "heavy" is a way of measuring weight.

and again, "the weight of an object is usually taken to be the force on the object due to gravity"

 

 

 

Gravitons, if proved to exist have no mass. So we go back to what SwansonT said

So you are defining "heavy" as having mass?

That's simple enough. Not sure if it's accurate though.

[studiot]

But what's the official definition?

 

Wikipedia says "In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co-exist and find use in their various contexts.^[2]"

 

If an apple is hanging from a tree, it's heavy. If it's in free fall, it's weightless. So it depends what it's doing.

 

I remember reading somewhere that if you trapped a photon between two perfect mirrors, the system gains rest mass, until the photon escapes. In inertial motion through curved space, the photon would be weightless and in free fall, but so would the apple.

 

I have to say that I understand and agree with the sentiment expressed here, although I find the exposition a trifle short.

 

 

I remember at school getting into trouble following a BBC educational programme aabout bouyancy.

 

The official explanation was

 

"Object float if they are lighter than water and sink if they are heavier"

 

and I was censured for daring to suggest that in fact objects denser than water sank.

 

Roll on a few years after I left school and some astronomy had enetered the physics curriculum; pupils are now taught that a given object weighs more on Earth than the Moon.

The heavier than water explanation is still common use, especially in primary schools however.

 

I come back to that victorian puzzle

 

Which weighs more a pound of feathers or a pound of lead?

 

Which has more mass?

 

Weight varies with location, mass does not.

 

So no, I would not define heavy as having mass.

[swansont]

According to Wikipedia, "heavy" is a way of measuring weight.

"According to wikipedia" is not a particularly rigorous response. It's on a disambiguation-type page, and it's wrong. Heavy is a way of comparing weight; it's a relative term. One thing can be heavier than another. One thing is heavy because it is heavier than some arbitrarily-chosen reference. You have provided no reference to be able to say that photons are heavy. In essence, you have defined the standard to be zero. Anything with energy is heavy. That definition differentiates nothing. It is useless.

 

Weight is generally defined as the gravitational force on an object. In reality, like when using a scale, it's the normal force required to be on an object at rest to oppose gravity.

 

None of that would let you say a photon has weight, since it has no mass. It also can't be at rest due to some normal force. In GR, which you invoke when mentioning curvature, gravity is not a force.

[EdEarl]

good discussion.

Light heavy is an oxymoron.

[Silvestru]

good discussion.

Light heavy is an oxymoron.

 

And Oxymoron is anagram for Onyx Room but I still really dont understand OP's initial question

 

Matter is transformed into energy so if there is light in the universe is it getting less massive. If yes what runs out first energy or matter?

 

Can you please rephrase?

[mistermack]

good discussion.

Light heavy is an oxymoron.

Tell that to Andre Ward.

 

Rather you than me !!

Edited May 19, 2017 by mistermack

[StringJunky]

My question is, is light heavy. Ive tried asking in other forums but don't get any good answers.

I've been told photons are massless but have momentum (a product of mass and velocity) so that doesn't make sense.

Matter is transformed into energy so if there is light in the universe is it getting less massive. If yes what runs out first energy or matter?

Momentum can be distinct from mass, as illustrated in the form of radiation pressure. When a photon is reflected or absorbed, momentum is transferred to that surface and can push the object if there's enough. Solar sails exploit the phenomenon.

 

 

 

 

More info: https://en.wikipedia.org/wiki/Solar_sail