Photons and Gravitons

[questor]

how is a photon created? how is a graviton created? in order for gravity to move at the speed of light, the mass must be no more than that of a photon. groups of photons can be seen with the naked eye, not so with gravitons. as far as we know gravity exists in all parts of the universe, light only emanates from clumps of matter. if there is a graviton, how did it instantaneously fill the universe after BB ? we can see light from objects as old as the birth of the universe, why can't we detect ancient gravitons?

[Erasmus00]

how is a photon created? how is a graviton created? in order for gravity to move at the speed of light, the mass must be no more than that of a photon. groups of photons can be seen with the naked eye, not so with gravitons. as far as we know gravity exists in all parts of the universe, light only emanates from clumps of matter. if there is a graviton, how did it instantaneously fill the universe after BB ? we can see light from objects as old as the birth of the universe, why can't we detect ancient gravitons?

 

First, no one is sure if gravitons even exist. They are postulated because in quantum field theory, all the forces are mediated by particles. In the attempt to unify gravity with quantum, we expect something with a particle nature.

 

Now, the reason your eye can detect photons is that it is designed to see photons, you don't have an organ designed to "see" gravity, though your inner ear might do the trick in a pinch.

 

Now, gravity and light emanate from matter. I don't know why you feel that gravity doesn't. Both gravity and light also "fill the universe" as you say. (the photon bath we are all sitting in is called the cosmic microwave background CMB).

 

We can't actually detect light from as old as the birth of the universe, the CMB is from the time when the universe first became transparent to light. The hope is that once we figure out how to detect gravitational waves, we will be able to probe back even further, because the universe should have been transparent to gravity waves before it was transparent to light.

-Will

[CraigD]

how is a photon created?

A photon is created when a fermion such as an electron or one of the 3 quarks making up a proton[/url], looses energy. Nearly all photons of visible light are produced when electrons change from one atomic orbital to another.

 

Photons are bosons. They’re not the only bosons that fermions emit and absorb, but they are the strongest, at anything but very close (<10^-15 m) ranges.

how is a graviton created?

Presumably, much like photons, but involving much (10^28 times) less exchange of energy.

 

I say “presumably”, because gravitons are still a very tentative and speculative addition to the Standard Model of particle physics. Unlike photons, which have been superbly useful in resolving many riddles of Physics, gravitons have proved difficult and troubling to include in the Standard Model, raising many theoretical problems and objections.

in order for gravity to move at the speed of light, the mass must be no more than that of a photon.

This statement matches my understanding of the current scientific consensus of some of the properties of the graviton.

groups of photons can be seen with the naked eye, not so with gravitons.

Photons or visible light are “seen” by their interaction with the electrons in the tissues of our eyes, and a complicated cascade of resulting neurochemical activity. Other photons, such as those in the infrared spectrum, are “felt” by their interaction with other nerves in our bodies, such as the peripheral nerves in our skin. Conducted heat is felt by these same nerves via the interaction of photons of magnetic interaction. We can indirectly “feel” other photons, such as ultraviolet or microwaves, the our nervous systems reaction to the trauma they cause our tissues.

 

In similar, indirect fashion, we feel the interactions of gravitational force with the atoms of our bodies, via both our kinesthetic nervous system, and the more sensitive equilibrioceptive system centered in our inner ears.

 

So, while gravitions and different kinds of photons are detected by different tissues in our bodies, it really not accurate to say we sense them in essentially different, or less direct, ways.

 

An important distinction between our ability to detect photons and gravitons is noteworthy: It is currently possible (with existing photomultiply technology – not quite with the naked eye), to accurately detect single photons of visible light. At 10^-28 times the energy of a typical photon, a technology capable of detecting a single graviton is unlikely to be created anytime soon, if ever. This is unfortunate, since such a capability could offer direct confirmation of their existence, in the same way that the photoelectric effect offered direct confirmation of the existence of photons.

as far as we know gravity exists in all parts of the universe, light only emanates from clumps of matter. if there is a graviton, how did it instantaneously fill the universe after BB ? we can see light from objects as old as the birth of the universe, why can't we detect ancient gravitons?

To the best of my knowledge, the universe is as full of gravity as it is of light, and the gravity and light from the most distant object we observe equally ancient. According to both the tentative extensions of particle physics describing the graviton and the classical theory of General Relativity, gravity did not instantaneously fill all of space, or fill it in any way significantly differently than light (due to the early opacity of the universe predicted by the Big Bang theory, one could argue that it got a 379,000 year head start, which is not very much for a 13,700,000,000 year-old universe)

 

I’m pretty sure gravitons will be a source of excitement, puzzlement, and controversy for many years to come.

[questor]

interesting replies. thanks. if a photon is ''created'' by a loss of energy, and energy is mass, what is left after the creation of the photon? photons move in waves and are easily detected by human observance as well as photometers of different kinds. not so for gravitons. does a graviton have energy? i guess if it has mass, it does, but why do we assume it travels in waves . maybe it doesn't travel at all. there is no evidence of gravity having reached us from a distant star.

[Erasmus00]

interesting replies. thanks. if a photon is ''created'' by a loss of energy, and energy is mass, what is left after the creation of the photon? photons move in waves and are easily detected by human observance as well as photometers of different kinds. not so for gravitons. does a graviton have energy? i guess if it has mass, it does, but why do we assume it travels in waves . maybe it doesn't travel at all. there is no evidence of gravity having reached us from a distant star.

 

First, keep in mind neither gravitons nor photons would be expected to have mass.

 

Now, the reason we believe gravity can travel in waves is because the best theory of gravity we have right now (general relativity) predicts that gravitational waves are possible. These waves would travel at the speed of light. We have a number of observations of binary stars that suggests that they are emitting gravitational waves, we just need to build devices sensitive enough to measure these waves.

-Will

[questor]

Erasmus,

'' First, keep in mind neither gravitons nor photons would be expected to have mass. ''

 

if there is no mass what is there and why does gravity bend rays of light?

[questor]

if photons are composed of particles, particles have mass, albeit small. if photons are composed of energy lost from a fragmenting nucleus, e= mc2, so at c there should be some mass equivilant ? don't all leptons, bosons have some mass?

[Erasmus00]

Erasmus,

'' First, keep in mind neither gravitons nor photons would be expected to have mass. ''

 

if there is no mass what is there and why does gravity bend rays of light?

 

The bending of light is a tricky problem of tremendous historical interest (it was one of the first confirmations of general relativity). To figure out how massless particles react to gravity, you need the full force of general relativity. In this theory, the paths through space that objects take are properties of the curved space time they travel through. Everything is affected by the curved space, not just things with mass. Consider in Newtonian theory, the acceleration of a body under gravity doesn't depend on its mass.

-Will

[Erasmus00]

if photons are composed of particles, particles have mass, albeit small. if photons are composed of energy lost from a fragmenting nucleus, e= mc2, so at c there should be some mass equivilant ? don't all leptons, bosons have some mass?

 

Photons are't composed of energy lost from a fragmenting nucleus. E=mc^2 applies to rest mass and rest energy, so if a photon has no rest mass, it has no rest energy. If you work out the relativistic formula for kinetic energy, you'll find that a particle traveling at c has inifinite energy, unless it has no rest mass

 

Now, all leptons have mass, but not all bosons. Photons, phonons, perhaps gravitons do not. W and Z bosons do. Any particle that travels at c must have a 0 rest mass.

-Will

[CraigD]

…if a photon is ''created'' by a loss of energy, and energy is mass, what is left after the creation of the photon?

The fermion – usually an electron – with slightly less mass (but never less than its rest mass)

photons move in waves and are easily detected by human observance as well as photometers of different kinds. not so for gravitons. does a graviton have energy?

Yes. The energy transferred by a single graviton, however, is tremendously (10^28 time) less than a typical photon

i guess if it has mass, it does,

Gravitons are postulated to have 0 mass.

 

According to the Standard Model, some bosons have mass, others don’t. Of the 5 elementary bosons (not including the graviton, which isn’t yet really an accepted part of the Standard Model), 2 – the photon and the gluon - have 0 mass, while the other 3 have mass >0.

 

While they have no rest mass, photons, which always travel at the speed of light, have momentum and energy, making it possible to consider them to have a sort of pseudo-mass. This is really a sort of illustrative make-believe, however – if a photon had any rest mass, no matter how small, then, according to Special Relativity, traveling at exactly the speed of light, it would have infinite energy, which they obviously do not.

but why do we assume it travels in waves .

In Quantum Mechanics, on which the Standard Model is based, every particle, lightspeed-traveling boson or slower moving fermion, is associated with a quantum wave function, allowing them to exhibit wave properties, yet, when an observer performs measurements to detect their presence in specific regions of space at specific intervals of time, to exhibit particle properties

maybe it doesn't travel at all. there is no evidence of gravity having reached us from a distant star.

There’s pretty good evidence that galaxies interact with one another gravitationally just as moons interact with planets, plants with stars, and stars with one another within galaxies. The structure of clusters of galaxies, which we have pretty good maps of, appear to show them orbiting, and on occasion being attracted to and colliding, with one another.

 

Note that this observational data is strong evidence that gravity works at an effectively unlimited distance, but not that it must be due to a boson, the graviton. There’s no guarantee that the graviton will ultimately become an accepted part of the Standard Model – a better theory may ultimately arise to explain gravity.

[questor]

i think certain bosons can travel thru dense objects such as the earth. why can't a photon do this? if there are partcles smaller than a photon, why can't they have more speed?

if a photon emanates from an object, what is the source of its propulsion, and how far will that photon travel?

[CraigD]

i think certain bosons can travel thru dense objects such as the earth. why can't a photon do this?

I think you’re thinking of the electron neutrino. Like the electron, it’s a lepton, meaning a fermion that isn’t a quark, but it has no charge, so can only interact via the 3 bosons of the weak nuclear force. Practically speaking, this means it is so likely to interact that most (but not quite all) neutrons can through a space full or other fermions, such as the quarks and electrons in the ordinary matter of the Earth without exchanging any bosons (interacting) at all. It makes them very difficult to detect, requiring setups like giant tanks of ultra-pure dry cleaning fluid (CCl4) deep underground, and years of watching, with most of your finds thrown out because they’re actually due to high-energy cosmic ray photons (which you’ve got to detect, so you don’t get false neutrino finds).

if there are partcles smaller than a photon, why can't they have more speed?

’Cause they’re not smaller than a photon.

 

Electron neutrinos, the least massive and most numerous kind, have very little mass, less that 1/100000 that of an electron, but that’s still much more mass than a photon’s 0. According to Relativity and the Standard Model, if a particle has any mass, it must move slower than the speed of light. If it has 0 mass, it must move exactly at the speed of light.

if a photon emanates from an object, what is the source of its propulsion, and how far will that photon travel?

Particle physics are quantum mechanical theories. Terms like “propulsion”, which are very useful for describing systems using big objects consisting of huge numbers of fundamental particles, such as cars and rockets, aren’t very useful when describing single fundamental particles. A photon can’t be still. It can only move at the speed of light. So speaking of “propelling” them doesn’t make sense.

 

What allows photons to be emitted by fermions, is a minute (or, sometimes, not so minute) changes in the fermion’s mass, which, in quantum mechanical terms, means a minute change in its wave function. It’s a very different way of thinking about matter, energy, space, time, and reality, but essential to understanding quantum mechanical theories.

 

A photons can travel forever (literally – they’re fundamental particles, so will never decay into a more fundamental particle), or until it interacts with another particle.

 

:) The basic terminology and concepts of the Standard Model are like a grand and beautiful jigsaw puzzle. The interaction of particles emitting, absorbing, and transforming into other particles is precisely defined by a collection of precise but difficult rules. Like a jigsaw puzzle, it can be very enjoyable or very frustrating to learn. While I’ve been vaguely aware of its existence for a couple of decades, I never formally studied it in school (I was a Math major, with an interest in Physics, but, in the 1980s, even Physics undergraduates were unlikely to have a class covering the Standard Model), and only began a serious effort to understand it earlier about 6 months ago. In the spirit of playing a fascinating game, I’d like for others in a situation similar to mine to join me in my studies, using scienceforums as a forum.

 

The wikipedia article “Standard model” (with pretty poster, suitable for printing and hanging) seems a good starting place. :eek:

[steelengineer]

the concept of a photon travelling at speed of light has changed over the past few years, try looking at the Scientific American articles on 'frozen light'.

Also, I have a feeling that if the concept of gravitons is established firmly enough, the interactions between gravitons and photons may give rise to an ether-like idea!!

[CraigD]

the concept of a photon travelling at speed of light has changed over the past few years, try looking at the Scientific American articles on 'frozen light'.

I’ve been a faithful SciAm reader for the past couple of decades. It’s good to meet another regular reader (or at least an effective researcher), in the person of steelengineer. Welcome!

 

Hau’s research, and his 7/2001 SciAm article, are amazing Physics, but don’t appear to challenge the Standard Model’s prediction that photons travel at exactly the speed of light in a vacuum.

 

Hau and other “frozen light” researchers are slowing light to nearly 0 by having the photons interact with the electrons in a cloud of atoms cooled to near absolute zero. These electrons absorb each photon, then reemit an identical photon. The time required for these 2 interactions is responsible for the photon crossing a distance in more time than a non-interacting photon requires.

 

There’s nothing unprecedented about this. The effective speed of light through ordinary high-refractive index materials is substantially reduced. Diamond, for instance, reduces it by about a factor of 2.4, without changing the photons’ frequencies or direction - that is, without scattering – them. What’s amazing about the condensed atom clouds in frozen light experiments is that they reduce the effective speed of light not by a factor of 2.4 or less, but by factors of 10,000,000 or more!

 

While its interactions with the supercool atoms are very slow, the actual speed of the photon from atom to atom is exactly the speed of light in a vacuum. All aspects of the phenomena are predicted by the Standard Model and the quantum mechanical model of the atom.

Also, I have a feeling that if the concept of gravitons is established firmly enough, the interactions between gravitons and photons may give rise to an ether-like idea!!

I think that most people are expecting the successful inclusion of gravitons into the Standard Model to make predictions of graviton-photon interactions consistent with Relativity. The idea of an luminescent ether in a absolute inertial frame, or “dragged” frames related to nearby masses have a lot of problems – they’re difficult to get to predict the observed behaviour of light (Eg: the Michelson-Morley experiment)

 

My feeling is that getting gravitons to make sense is going to be quite a challenge, and may require profound revisions to the Standard Model. How, when, or even if it will be resolved, is hard to guess.

[steelengineer]

My feeling is that getting gravitons to make sense is going to be quite a challenge, and may require profound revisions to the Standard Model. How, when, or even if it will be resolved, is hard to guess.

 

I think the problem, once again, is with our fundamentals. we assign a 2-D model to a wave that actually exists in 3-D, when we categorize the electromagnetic waves as being sinosoidal. I think if we give them a helix-like form, the different forms of energy: the strong, weak, electromagnetic, and gravitational energy can be transformed into the wave-form and hence combined. what do you think?

 

also, look at my posting regarding the convergence of dimensions.