Why Doesn't a Photon's Energy Knock Us Out?

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In summary, photons have zero rest mass, but they do have momentum. When they reach the speed of light, the energy they take to get there causes them to gain mass until they reach a point where the energy it takes to overcome light speed would be infinite.
  • #1
CBR600RR
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Let me preface this question by saying that it might be silly because I might have the facts wrong, but I'll ask anyway.
If a photon is a "little packet/bundle of energy", the photon (energy) should contain some mass, even if it is tiny, since Einstein stated mass and energy are interchangeable. Now when this mass is accelerated toward the speed of light it needs energy to "push" it to a higher speed. When the photon starts getting closer to the speed of light, the energy that it takes to get it there starts to cause the particle to gain mass until it reaches a point where the energy it takes to overcome light speed would be infinite.
My question is that if the photon has so much energy how come when a photon hits a human it doesn't "knock him/her out cold"?

Like I said this may be a stupid question. I think I am just missing something really easy that I should know, so feel free to rip my statement apart and add any new info I am missing.
 
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  • #2
Photons have zero rest mass. Photons travel at the speed of light from the time they are born. They do not speed up from a slower speed. You cannot think of them as small masses being speeded up. They do not have "infinite" energy, or anything close to it.
 
  • #3
What causes them to travel at the speed of light. Are you saying that they go from zero to 180,000 miles per second in an instant?

P.S. I am not questioning you to be stubborn, I'm just trying to get the answer :approve:
 
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  • #4
CBR600RR said:
What causes them to travel at the speed of light. Are you saying that they go from zero to 180,000 miles per second in an instant?

P.S. I am not questioning you to be stubborn, I'm just trying to get the answer :approve:

Photons never speed up, or slow down. They travel at 'c' from the instant they are created.

The situation in a physical media gets a bit tricky. One of the best ways of thinking about it is that the photon travels at 'c', always, even in a media, but occasionally gets absorbed and re-emitted.

Note that the speed of energy transmission through a media thus can be slower than 'c', due to the photons being absorbed, held for a very short while, then re-emitted.
 
  • #5
CbR

Depending on the frequency and interaction with different electromagnetic waves, photons "can knock you out cold "
 
  • #6
who said that photons don't hit the humans?!

photons have momentum, since they have mass.

but the problem is in the misunderstanding of the nature of the photons mass.Photons have relativestic mass, but not a rest mass.

even though, it still has momentum, and that was proven..
 
  • #7
Photons do not have mass. They do have momentum. Only massless particles are permitted to travel at c, in fact, they are forbidden to travel at any other speed.
 
  • #8
I thought that photons do have mass since a gravitational field "bends" them when they encounter it. How does gravity attract/affect something with a zero mass?
 
  • #9
Since a photon is generated by an electron, they're both right.
 
  • #10
CBR600RR said:
I thought that photons do have mass since a gravitational field "bends" them when they encounter it. How does gravity attract/affect something with a zero mass?
Gravity bends space. Photons always travel the shortest distance between two points [a straight line]. In curved space, the shortest distance between two points is a geodesic [a curved line].
 
  • #11
CBR

All in all your question is actually a brilliant question. Physicists argue if photons are EM or just a wave duality of a particle without mass.
There is no consclusive answer as of today.
 
  • #12
CBR600RR said:
I thought that photons do have mass since a gravitational field "bends" them when they encounter it. How does gravity attract/affect something with a zero mass?

The general relativity gravity couples to energy density, not just mass. Light does not have mass, but it does have energy, and thus it gravitates.
 
  • #13
Would the rest mass of photons actually be non zero, then the theory of quantum electro-dynamics would have to be re-written :confused:
 
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  • #14
Virtually all of existing physics would have to be rewritten for the photon to have mass. Simply put, every experiment ever done to date would not have have worked if the photon actually had mass.

- Warren
 
  • #15
One of my friends told me that photons would have to have mass or they couldn't exist. I told him that if they did have mass a photon would knock you on your arse and turning on a light would cost you a fortune when your power bill arrived.
 
  • #16
UNLESS, the entire light theory as we know it is reversed.
What IF photons are constantly in the air, but connect to an electron the moment it is energized - it connects to it at the speed of light ...when it becomes visible, or not, depending on frequency.
 
  • #17
CBR600RR said:
I thought that photons do have mass since a gravitational field "bends" them when they encounter it. How does gravity attract/affect something with a zero mass?

Photons are affected by a gravitational field. But in GR, energy generates the gravitational field, not mass. To be more precise, it's the stress-energy-tensor that generates the gravitatioanl field - under most circumstances, however, only the component T_00 of this tensor, which represents energy density, is important.
 
  • #18
whydoyouwanttoknow said:
One of my friends told me that photons would have to have mass or they couldn't exist. I told him that if they did have mass a photon would knock you on your arse and turning on a light would cost you a fortune when your power bill arrived.
Your friend is incorrect. A photon has no mass, merely momentum. He is, however, right about the power bill.
 
  • #19
Chronos said:
Your friend is incorrect. A photon has no mass, merely momentum. He is, however, right about the power bill.

I said the power bill would cost you a fortune. That'd be correct right propelling a particle with mass to the speed of light.
 
  • #20
Oops said:
CBR

All in all your question is actually a brilliant question. Physicists argue if photons are EM or just a wave duality of a particle without mass.
There is no consclusive answer as of today.
That question has already been answered. As far as I can see. The fact you have a computer that works is pretty compelling evidence.
 
  • #21
whydoyouwanttoknow said:
I said the power bill would cost you a fortune. That'd be correct right propelling a particle with mass to the speed of light.
If the particle had mass, it could never be propelled to the speed of light, even if the power company had access to all the energy in the universe ... of course, if the particle were an electron, and the power company allowed you to have as much power as a small city (and you could covert the energy to making the electron go faster efficiently), your electron would be moving very close to the speed of light :wink:

Do you know how to calculate how close to the speed of light it would go?
 
  • #22
Nereid said:
If the particle had mass, it could never be propelled to the speed of light, even if the power company had access to all the energy in the universe ... of course, if the particle were an electron, and the power company allowed you to have as much power as a small city (and you could covert the energy to making the electron go faster efficiently), your electron would be moving very close to the speed of light :wink:

Do you know how to calculate how close to the speed of light it would go?
My guess would be very close to c. I am curious, nereid, why you waited so long to jump in?
 
  • #23
'long'? The thread only began after 22:00 on the 17th!

Will you miss me if I'm away for three weeks then? :wink:
 
  • #24
My bad, of course I would. The injections of reasonable thought is sorely missed here these days.
 
  • #25
The way I explain the photon to myself to account for the fact it has no mass is to bear in mind that it is a wave in an electric field. The properties of an electric field are such that it propagates all disturbances to it at one speed only, c, no faster, no slower and while it can transfer the energy of a disturbance from one location to another, no mass whatever accompanies that transference, just energy. The field is real, but its reality is limited, somehow, to the function of a potential direction for the travel of its waves. The photon has no mass because the medium that carries it, the electric field, has no mass. The photon is the energy of a small, intense disturbance to the position of the electron, traveling away from the electron via its electric field, at the only speed the field is capable of propagating such disturbances.
 
  • #26
Nereid said:
If the particle had mass, it could never be propelled to the speed of light, even if the power company had access to all the energy in the universe ... of course, if the particle were an electron, and the power company allowed you to have as much power as a small city (and you could covert the energy to making the electron go faster efficiently), your electron would be moving very close to the speed of light :wink:

Do you know how to calculate how close to the speed of light it would go?

I told him to get a particle with mass to the speed of light you'd need infinite energy and that would cost you. :rofl:

I don't know how to calculate anything with this stuff. I just read this stuff for fun. :eek:
 
  • #27
whydoyouwanttoknow said:
I told him to get a particle with mass to the speed of light you'd need infinite energy and that would cost you. :rofl:

I don't know how to calculate anything with this stuff. I just read this stuff for fun. :eek:

Read the rules for posting.
 
  • #28
zoobyshoe said:
The way I explain the photon to myself to account for the fact it has no mass is to bear in mind that it is a wave in an electric field.
Not entirely, it is a dual wave-particle thing. That is hard to conceptualize, but it is the best known description.

The properties of an electric field are such that it propagates all disturbances to it at one speed only, c, no faster, no slower and while it can transfer the energy of a disturbance from one location to another, no mass whatever accompanies that transference, just energy.
Technically, that is not a property of an 'electric field'. It is a property of all massless particle. That distinction is important.
The field is real, but its reality is limited, somehow, to the function of a potential direction for the travel of its waves. The photon has no mass because the medium that carries it, the electric field, has no mass. The photon is the energy of a small, intense disturbance to the position of the electron, traveling away from the electron via its electric field, at the only speed the field is capable of propagating such disturbances.
Field effects are not limited and there is no 'medium that carries' it. To say otherwise implies 'aether'. A photon is emitted when an electron falls to a lower energy level [which normally only occurs after it receives energy from an incoming photon]. After that, the photon is on its own.
 
  • #29
Chronos said:
Not entirely, it is a dual wave-particle thing. That is hard to conceptualize, but it is the best known description.
The way this was explained to me the other day in another thread was that all EM energy is essentially waves but that at a certain point the waves become so short and compact that they begin to interact with everything else as particle-like packets of energy. This made a lot of sense and no one came along and objected to it.
Technically, that is not a property of an 'electric field'.
Not quite sure if you mean it's not exclusively the property of the elecric field or if you mean nothing propagates in an electric field at c?
It is a property of all massless particle. That distinction is important.
I had no idea there were any other massless particles besides photons. Which are they ?
Field effects are not limited and there is no 'medium that carries' it. To say otherwise implies 'aether'.
I'm not suggesting that there is a medium for the electric field. It is its own thing, and isn't the aether. The electric field, to the best of my knowledge, is the medium for EM energy.
A photon is emitted when an electron falls to a lower energy level [which normally only occurs after it receives energy from an incoming photon]. After that, the photon is on its own.
The other day someone suggested things to the effect the photon wasn't "on it's own". I had actually previously thought it was. The question came up when I asked where the transition from EM "wave" in a field to independent photon occurred in the EM spectrum. This person said there was no actual transition, it was all the same thing, but that the waves become short enough at some point to exhibit exclusively "particle-like" behaviours in interactions.
 
  • #30
zoobyshoe said:
I had no idea there were any other massless particles besides photons. Which are they ?
AFAIK, the only one we know of today would be the neutrino. All three types - electron, mu, tau - have no measurable mass, in the best experiments to date (though the mass of tau possible within experimental limits is still huge). For quite some time many thought that all neutrinos were massless. However, in the last decade it's become clear that neutrinos are sneaky little things - they 'oscillate' between 'flavours'; different mixtures of flavours give each of the types we observe. Unless there's some really new physics involved that we are quite unaware of, this behaviour means that at least one neutrino flavour has mass, and possibly all three (I'm not so sure of this last point).

In the theoretical physicists' zoo, there are many a new particle waiting to be found - it depends on how the Standard Model is extended, modified, or supplanted. As there are no solid observations to guide one around this hypothetical zoo, one is free to consider any - or none - of them seriously. No doubt someone else will make a post about their favourites, including any that are massless (the graviton, for example).
 
  • #31
Thanks, Nereid. Those neutrinos sound like a fine can of worms to try to sort out.
 
  • #32
Nereid, the gluons, which of course are not observed, are also massless, along with the photon. These are all bosons. The neutrinos, before the recent discoveries, were regarded as the only massless fermions.
 
  • #33
selfAdjoint said:
Nereid, the gluons, which of course are not observed, are also massless, along with the photon. These are all bosons. The neutrinos, before the recent discoveries, were regarded as the only massless fermions.
Oops, :redface: Clearly my coffee wasn't strong enough (or last night's wine too good).

So the carriers of two of the forces are massless, and the carriers of one quite massive (and the graviton is hypothetical), with all force carriers being bosons.

Does the gluon travel at c?
 
  • #34
Nereid said:
Does the gluon travel at c?

Necessarily it does, since it's massless, and the standard model obeys special relativity, because the Lorentz transformations require that for a massless body.
 
  • #35
Neutrinos are flavorful, gluons are colorful.

"In quantum chromodynamics (QCD), today's accepted theory for the description of the strong nuclear force, gluons are exchanged when particles with a color charge interact. When two quarks exchange a gluon, their color charges change; the gluon carries an anti-color charge to compensate for the quark's old color charge, as well as the quark's new color charge. Since gluons thus carry a color-charge themselves, they can also interact with other gluons, which makes the mathematical analysis of the strong nuclear force quite complicated and difficult. Even though there are theoretically nine unique colour combinations for gluons, (r-ar, r-ag, r-ab, g-ar, g-ag, g-ab, b-ar, b-ag, and b-ab) in reality there are only eight."


Gluon
Address:http://www.fact-index.com/g/gl/gluon.html
 
<h2>1. Why don't photons knock us out?</h2><p>Photons are particles of light that have energy, but they do not have mass. This means that they do not have the ability to physically interact with our bodies and cause us harm, such as knocking us out. Additionally, the energy of a single photon is very small and not enough to cause any noticeable effects on our bodies.</p><h2>2. What determines the energy of a photon?</h2><p>The energy of a photon is determined by its wavelength or frequency. The shorter the wavelength or the higher the frequency, the more energy the photon has. This is why high energy photons, such as X-rays and gamma rays, can be harmful to our bodies.</p><h2>3. Can photons cause any harm to our bodies?</h2><p>While photons themselves do not have the ability to knock us out, they can still cause harm to our bodies through their energy. High energy photons, such as those found in X-rays and gamma rays, can damage our cells and DNA, leading to potential health issues.</p><h2>4. How do our bodies interact with photons?</h2><p>Our bodies interact with photons through a process called absorption. When photons come into contact with our bodies, they can be absorbed by atoms and molecules, causing them to vibrate and release heat. This is how we are able to feel the warmth of sunlight on our skin.</p><h2>5. Are there any other factors that affect how photons interact with our bodies?</h2><p>Yes, there are several other factors that can affect how photons interact with our bodies. These include the intensity of the light, the duration of exposure, and the type of tissue or material that the photons are interacting with. These factors can determine the amount of energy that is absorbed by our bodies and can impact the potential harm that photons can cause.</p>

1. Why don't photons knock us out?

Photons are particles of light that have energy, but they do not have mass. This means that they do not have the ability to physically interact with our bodies and cause us harm, such as knocking us out. Additionally, the energy of a single photon is very small and not enough to cause any noticeable effects on our bodies.

2. What determines the energy of a photon?

The energy of a photon is determined by its wavelength or frequency. The shorter the wavelength or the higher the frequency, the more energy the photon has. This is why high energy photons, such as X-rays and gamma rays, can be harmful to our bodies.

3. Can photons cause any harm to our bodies?

While photons themselves do not have the ability to knock us out, they can still cause harm to our bodies through their energy. High energy photons, such as those found in X-rays and gamma rays, can damage our cells and DNA, leading to potential health issues.

4. How do our bodies interact with photons?

Our bodies interact with photons through a process called absorption. When photons come into contact with our bodies, they can be absorbed by atoms and molecules, causing them to vibrate and release heat. This is how we are able to feel the warmth of sunlight on our skin.

5. Are there any other factors that affect how photons interact with our bodies?

Yes, there are several other factors that can affect how photons interact with our bodies. These include the intensity of the light, the duration of exposure, and the type of tissue or material that the photons are interacting with. These factors can determine the amount of energy that is absorbed by our bodies and can impact the potential harm that photons can cause.

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