'nothing, not even light'

[nokhor]

one of my greatest pet peeves is that whenever i read an astronomical article that invovles black holes they almost always have to use the stock phrase "nothing, not even light, can escape" its gravitational pull.

i don't understand, is it mandatory to use that phrase? do writers get penalized by their editors if they don't use it? is there a pro plagiarism commitee that enforces using the phrase? its never 'black holes, one way traffic' or 'black holes, what goes in doesn't come out'. its always "nothing, not even light" as if they hadn't reminded me, i might not have realized that light is something and not nothing. or when i think of 'nothing' i usually consider light one of its attributes.

[R'as al Ghul]

LOL.
I know what you mean. Isn't light generally considered to have no mass?
Not sure but this could be meant to emphasize the gravitational pull.
But I agree with you.
Didn't Stephen Hawking lately say that in fact there's a
remaining radiation emitting from the black holes? He revised his own theory
that nothing could escape. I think two jets of energy are propelled into space?

[nokhor]

yeah its called hawking radiation, but it's just that overused phrase that bugs me.

[Duke of Gloucester]

To escape the gravitational field of an object such as a planet or star, you need to be travelling at a certain minimum speed, or eacape velocity. IIRC the escape velocity at the surface of the earth is about 11 km/s. The escape velocity of a black hole is greater than the speed of light. Since nothing can move faster than light nothing can escape from a black hole.

According to the Theory of Relativity, light does have mass and is affected by gravitational fields. Light cannot escape from a black hole. It would actually be more accurate to say no electromagnetic radiation can escape. Hawking radiation is emitted from the space around a black hole.

[Louis VI the Fat]

:laugh4:
This is so very true!
And to make matters worse, it appears to be some form of global conspiracy:

Rien, pas même la lumière, ne peut s'échapperYou can't read about a black hole in French without the above phrase turning up. It translates word by word as: 'nothing, not even light, can escape'.

So who did invent this phrase anyway?

[English assassin]

Didn't Stephen Hawking lately say that in fact there's a
remaining radiation emitting from the black holes?

As the duke says its not from actually within the black hole. Quantum fluctuations produce pairs of virtual photons very close to the event horizon, one falls into the black hole leaving the other to carry on into real space as radiation "from" the black hole. He has recently published something more on it, something to do with a problem of infinite red shift or something. its all a bit beyond me.


Rien, pas même la lumière, ne peut s'échapper

I will now memorise this as a useful french phrase, and use it to appear enigmatic in France. It is a great step forward from Ou se trouve la gare?

So what ought to be replacing

[Ironside]

According to the Theory of Relativity, light does have mass and is affected by gravitational fields. Light cannot escape from a black hole. It would actually be more accurate to say no electromagnetic radiation can escape. Hawking radiation is emitted from the space around a black hole.

From what I know light doesn't have a mass but does act as it had one in several aspects. If light does have mass, then the Theory of Relativity says that this mass is unlimited and that would create a huge black hole that consumes the hole universe. :laugh4:

And IIRC Hawking radiation never really escapes the black hole. It's a radom creation of 2 particles on the exact edge of the black hole. One escapes and the other is getting drawn into the black hole. It also prevents the particles to destroy eachother as they usually do.

And I've found a source that didn't use 'nothing, not even light, can escape' in Swedish :2thumbsup:

[Ronin]

From what I know light doesn't have a mass but does act as it had one in several aspects. If light does have mass, then the Theory of Relativity says that this mass is unlimited and that would create a huge black hole that consumes the hole universe. :laugh4:

And IIRC Hawking radiation never really escapes the black hole. It's a radom creation of 2 particles on the exact edge of the black hole. One escapes and the other is getting drawn into the black hole. It also prevents the particles to destroy eachother as they usually do.

And I've found a source that didn't use 'nothing, not even light, can escape' in Swedish :2thumbsup:


I remember an old experient in physics class back in high-school that would prove that light has mass.....

it consisted of a glass container that was in a vacuum situation, in this container there was this device that kinda looked like a top, it was set in an axil that allowed it to spin, now...one of the sides of this thing was reflective, with the oposite side was black......when sun light shined on this device the little top thing inside spun around.....I can´t remember the name of the bloody thing in portuguese let alone in english...but if i can find a picture i´ll post it.:wall: :juggle2:

[Duke of Gloucester]

From what I know light doesn't have a mass but does act as it had one in several aspects. If light does have mass, then the Theory of Relativity says that this mass is unlimited and that would create a huge black hole that consumes the hole universe.

Light does have mass. The mass of a given photon is hf/c^2 where h is Plancks constant, c is the speed of light and f is the frequency of the photon. E=mc^2 tells us that mass and energy are basically the same thing, and since photons have energy, they must have mass.

The equipment Ronin describes is called a Crooke's radiometer, but in spite of what some school teachers tell you, it does not rotate because it is being knocked by photons. It rotates because the black sides are hotter than the silver sides. See the link:
http://www.physics.brown.edu/physics/demopages/Demo/thermo/demo/4d2010.htm

[Beirut]

~:cheers:
one of my greatest pet peeves is that whenever i read an astronomical article that invovles black holes they almost always have to use the stock phrase "nothing, not even light, can escape" its gravitational pull.

i don't understand, is it mandatory to use that phrase? do writers get penalized by their editors if they don't use it? is there a pro plagiarism commitee that enforces using the phrase? its never 'black holes, one way traffic' or 'black holes, what goes in doesn't come out'. its always "nothing, not even light" as if they hadn't reminded me, i might not have realized that light is something and not nothing. or when i think of 'nothing' i usually consider light one of its attributes.

I've had exactly the same thought for years! ~:cheers:

[Big_John]

photons are considered to have no "rest mass".. but since they never rest, it's ok to treat them as massive particles. ~;)

also, there's a bit more to hawking radiation than disassociated particle pairs.. QM allows for particles "within" the black hole to momentarily acquire enough energy to overcome the event horizon. iirc, it's a situation similar to quantum tunneling. i think that's still a rather speculative theory, and i'm not sure if QM is even supposed to hold at event horizons.. but i think that is thought to be another way that we can learn about the inner workings of black holes (along with the quantum entanglement of particle pairs).

[Duke of Gloucester]

photons are considered to have no "rest mass".. but since they never rest, it's ok to treat them as massive particles.

It is "ok" if "ok" can be used as a synonym for "correct"~;)

[Seamus Fermanagh]

Is this yet another phrase for which we should exhume Carl Sagan and beat the bejeebers out of him -- or does it predate that eminent MC of physics?

[Big_John]

It is "ok" if "ok" can be used as a synonym for "correct"~;)#5
:elephant:

http://dictionary.reference.com/search?q=ok

[Duke of Gloucester]

OK, your use of OK is obviously OK!~;)

[Papewaio]

Light does have mass. The mass of a given photon is hf/c^2 where h is Plancks constant, c is the speed of light and f is the frequency of the photon. E=mc^2 tells us that mass and energy are basically the same thing, and since photons have energy, they must have mass.


Photons do not have a mass, all the mass is in the form of energy. They do however have momentum.

If they had any mass then they would have infinite mass at the speed of light.

As for the light being bent by gravity, it is the very fabric of space being warped that causes that. The effect would be stronger if photons had a tiny mass... and the amount that the light bends due to gravity would change dependent on the mass... since they all have zero rest mass, the light is all bent by the same amount.

If photons had different masses then gravitational lensing would cause chromatic dispersion.

[Duke of Gloucester]

Sounds convincing, Pape, but I don't think any of your post is correct.


Photons do not have a mass, all the mass is in the form of energy. They do however have momentum.

Special relativity tells us that mass and energy are the same thing, so if photons have energy, they must have mass. Momentum is the product of mass and velocity, so if they have momentum, they must have mass. However, as Big John says, they have zero rest mass. Of course they cannot exist at rest so whenever photons exist, they have mass.



If they had any mass then they would have infinite mass at the speed of light.

This is not quite right. If they had any rest mass, they would have infinite mass at the speed of light.


As for the light being bent by gravity, it is the very fabric of space being warped that causes that. The effect would be stronger if photons had a tiny mass... and the amount that the light bends due to gravity would change dependent on the mass... since they all have zero rest mass, the light is all bent by the same amount.

You seem to be distinguishing between gravity and the bending of space/time, but gravity is the bending of space time. The bending of space time is what causes you to return to earth and the planets to orbit the sun as well as bending the paths of photons. As for the interesting notion of chromatic aberation with gravitational lensing effects, a moment's consideration will tell you that this is not correct. A red photon has less mass than a blue one, but it also has less inertia, and therefore its deflection by a gravtiational field is the same. The same argument applies to the hammer and feather dropped on the moon. The curvature of space/time is a different way of explaining the same thing both for the blue and red photons and the hammer and feather.

[Papewaio]

Special relativity tells us that mass and energy are the same thing, so if photons have energy, they must have mass. Momentum is the product of mass and velocity, so if they have momentum, they must have mass. However, as Big John says, they have zero rest mass. Of course they cannot exist at rest so whenever photons exist, they have mass.

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html


If the rest mass of the photon was non-zero, the theory of quantum electrodynamics would be "in trouble" primarily through loss of gauge invariance, which would make it non-renormalizable; also, charge-conservation would no longer be absolutely guaranteed, as it is if photons have vanishing rest-mass. However, whatever theory says, it is still necessary to check theory against experiment.

http://www.everything2.com/index.pl?node=photon


Photon Mass
Mass is a confusingly misused term. We all know Einstein's rather famous mass-energy equivalence, E=mc², and it's fairly obvious that photons have energy, so they must have mass, right? Well, no. The correct way to interpret E=mc² is to use it define the energy of an object when it is not moving, or rest energy, E0, in terms of a fixed quantity, it's mass. This is sometimes emphasised by calling this value the rest mass, but this isn't helpful, a particle only has one mass, it may have variable energy depending on how fast it is travelling, but mass is constant.

When a particle is moving the total energy is given correctly by, E² = m²c4 + p²c², where p is momentum. You can see if the object is at rest then p²c²=0, and the equation reduces back to E0=mc². In the case of a massless, but moving, particle then it reduces to E=pc. This means that a particle can have energy without mass. You can't stop photons so they always have momentum.

Theoretically, if photons did have mass we would see deviations from the Coulomb inverse square law. It is photons that transfer the electromagnetic force, they are gauge bosons. If they are massless then they can have infinite range and the 1/r² law holds true, if they have mass, they become limited in their range so the 1/r² rule will not hold anymore. Experimental tests for photon mass concentrate on finding such deviations. The upper limit for photon mass so far stands at 3x10-27 eV, which is about 10-46 kg.

[Divinus Arma]

The gravitational field is so strong that the escape velocity near it exceeds the speed of light. This implies that nothing, not even light, can escape its gravity, hence the word "black."
http://www.crystalinks.com/black_holes.html


Formed in one of three main processes, they exert so much gravitational force that nothing - not even light - can escape their pull.
http://home.cwru.edu/~sjr16/stars_blackhole.html


Black holes are places in space where the force of gravity is so strong that nothing, not even light, can escape
http://news.nationalgeographic.com/news/2005/05/0524_050524_blackholes.html


By a score of 135 to zero, scientists using NASA's Rossi X-ray Timing Explorer have compared suspected neutron stars and black holes and found that the black holes behaved as if each one has an event horizon, the theoretical border from beyond which nothing, not even light, can escape.
http://www.physorg.com/news9693.html


If a star, for example, collapses beyond some critical radius, Rc, the gravitational forces at the surface will be so great that the escape velocity of any object will be greater than the speed of light. According to Einstein, then, once this critical radius is reached, nothing, not even light will be able to escape from the surface of the star.
http://theory.uwinnipeg.ca/mod_tech/node61.html


A black hole's immense gravity accelerates nearby matter and energy, which spirals inward and eventually reaches the speed of light. At that speed, the incoming stuff crosses a so-called "event horizon," a sphere beyond which events cannot be seen because nothing, not even light, comes back out.
http://www.space.com/scienceastronomy/astronomy/desktop_blackhole_010123.html


A team of astronomers from MIT and Harvard have observed that a certain kind of explosion seen on neutron stars is never seen coming from black holes. This is strong evidence for the existence of a black hole's event horizon; the point at which nothing, not even light, can escape from its grasp.
http://www.universetoday.com/am/publish/event_horizon_measured.html


Black holes are celestial objects with gravity so intense that nothing, not even light, can escape from them once past their boundary, called the event horizon.
http://www.gsfc.nasa.gov/topstory/20020626bhlight.html


One way to make a black hole, theorists agree, is to explode a very massive star. In one of these supernova events, outer portions of the star are flung into space. Some material falls back, however, and collapses into a sphere so dense that nothing, not even light, can escape.
http://www.space.com/scienceastronomy/blackhole_birth_030319.html

It had to be done. The list of google returns creates an event horizon and goes on for eternity until nothing, not even light, can escape.

LOL:laugh4:

Custom user title worthy!!!

[Duke of Gloucester]

Thanks Pape. You turn your back for two decades and suddenly your degree is out of date. Sounds as if I was a bit short with DJ as well. My apologies. Saying it is ok to regard photons as having mass sounds generous in view of Pape's links. Mind you I think that it takes a theortical physicist to say that a photon has momentum, inertia and experiences gravity but does not have any mass. This probably explains why Stephen Hawking uses mass to mean relativistic mass in his popular works. Just goes to show are never to old to learn something new.

[The_Mark]

I remember an old experient in physics class back in high-school that would prove that light has mass.....

it consisted of a glass container that was in a vacuum situation, in this container there was this device that kinda looked like a top, it was set in an axil that allowed it to spin, now...one of the sides of this thing was reflective, with the oposite side was black......when sun light shined on this device the little top thing inside spun around.....I can´t remember the name of the bloody thing in portuguese let alone in english...but if i can find a picture i´ll post it.:wall: :juggle2:
It's a radiometer, but it doesn't prove that light has a mass. The experiment proves that the gas molecules inside (the thing doesn't contain a complete vacuum) take heat off the black side, expanding the gas on the black side of the squares, resulting in differences of pressure (pushing the black side a bit) and resulting in a flow of gas molecules around the little squares from the colder side to the warmer, giving the spinning thing more speed.

[Sardo]

This thread has put so much pressure on my brain, that nothing, not even light can get into it anymore.

:dizzy2:

[Papewaio]

Thanks Pape. You turn your back for two decades and suddenly your degree is out of date. Sounds as if I was a bit short with DJ as well. My apologies. Saying it is ok to regard photons as having mass sounds generous in view of Pape's links. Mind you I think that it takes a theortical physicist to say that a photon has momentum, inertia and experiences gravity but does not have any mass. This probably explains why Stephen Hawking uses mass to mean relativistic mass in his popular works. Just goes to show are never to old to learn something new.

As for the second bit about the hammer + feather analogy you are correct, the mass of the orbiting object cancels out when calculating the accelaration of it.

[Louis VI the Fat]

When a particle is moving the total energy is given correctly by, E² = m²c4 + p²c², where p is momentum. You can see if the object is at rest then p²c²=0, and the equation reduces back to E0=mc².Yes, I was about to bring that up.






Ok, so I was not.

So which is it. Does light escape or not? :dunce:

[Papewaio]

Photons not being able to escape black holes is a consequence of relativity. Photons being massless means that gravity has to warp space... if it was just a force of attraction between two masses then photons would ignore gravity.

The very definition of a black hole is a star which has such a huge gravity that light cannot escape. Making something that would otherwise produce massive amounts of light a black hole. The escape velocity for a black hole is faster then the speed of light. As light is the maximum speed that objects can travel by saying that not even light can escape means that nothing can escape from within the event horizon at all.

The concept was first talked about by John Mitchell (http://en.wikipedia.org/wiki/John_Michell) in 1784. Where he discussed the size of a star needed to be greater then the escape velocity of light.

[Uesugi Kenshin]

So why do we have a term for tachyonic particles? (faster than light)

Is there absolutely no factual basis for such things and it is mere sci-fi with not even a dedicated lunatic fringe talking about them in as real?

Just curious.

[Papewaio]

A tachyon is as of yet hypothetical... if they do exist they would always travel faster then light...

[Uesugi Kenshin]

That's what I figured. Well it still makes for great sci-fi. :2thumbsup:
Thanks Pape.