black holes and light

Shrykull · Post by **Shrykull** » 2003-03-07 08:43pm

If weight is the response of mass (and yes, what is mass? I thought it was the amount of matter an object contains, but I saw something on this site about "moles" being the measurement unit) to the pull of gravity and light(like all other EM radiation) mass, how can it be pulled into a black hole?

Cap'n Hector · Post by **Cap'n Hector** » 2003-03-07 08:46pm

Light, as a particle, has mass. It's not much mass, to be sure, but it has a low mass.

Moles are a measurement of the number of molocules in a certain volume. Can't recall what the volume is ATM.

kojikun · Post by **kojikun** » 2003-03-07 08:59pm

light has no real mass but it has virtual mass equivalent to the energy in the photon.

Xenophobe3691 · Post by **Xenophobe3691** » 2003-03-07 09:04pm

If you think of space as a grid, light follows the lines in the grid.

Objects bend the grid towards them, light still follows the lines in the grid, but they are bent towards the object.

With a black hole, the lines are severely curved. Inside the event horizon, the Lines actually circle back to the singularity. All straight paths lead back to the black hole. Therefore, even though light has negligible mass, it still gets pulled in.

I hope this helps...

SyntaxVorlon · Post by **SyntaxVorlon** » 2003-03-07 10:27pm

Notably it has been found that light can escape from black holes, and thus is probably traveling just as fast relative to the bh as it does to us in normal space, but because of the extreme curvature of the skein it travels far slower than regular c.

Mad · Post by **Mad** » 2003-03-07 10:28pm

Cap'n Hector wrote:Light, as a particle, has mass. It's not much mass, to be sure, but it has a low mass.

Light has no mass. It has momentum, but no mass. If it had mass, then it wouldn't be able to travel at c, as any particle with mass would require infinite energy and mass to travel at lightspeed.

Wicked Pilot · Post by **Wicked Pilot** » 2003-03-07 10:33pm

For those of you unfamiliar with moles:

Mass is a measure of matter. A mole is the measurement of the number of atoms in a substance made of one element. Specifically defined, one mole is the number of atoms in a 12g sample of carbon-12. There are 6.02x10^23 particles per mole. This ratio is known as "Avogadro's Number". To find the number of particles in a known mass, you simply take the mass, devide it by the atomic weight of the element, and that will give you your moles. Multiply that by Avogrado's number, and you know the total amount of atoms in the sample.

For example, we have a 112g block of iron (56Fe), and we want to determing how many iron atoms are in it. We simple take 112g, and devide it by the atomic weight of 56Fe, and that will give us our moles in the sample:

112g / 56g/mol = 2 moles.

To get our atom count, we simply multiply the number of moles by Avogadro's number, and presto, you get an answer:

2 moles * 6.02*10^23 atoms/moles = 1.42*10^24 atoms.

kojikun · Post by **kojikun** » 2003-03-07 10:49pm

how many atoms, or how many molecules, etc. one mole of water, for instance, contains 1 mole oxygen and 2 moles hydrogen (every particle of water has two hydrogen, remember)

Wicked Pilot · Post by **Wicked Pilot** » 2003-03-07 10:53pm

kojikun wrote:how many atoms, or how many molecules, etc. one mole of water, for instance, contains 1 mole oxygen and 2 moles hydrogen (every particle of water has two hydrogen, remember)

I could be wrong, but I'm quite sure it's 6.02*10^23 water molecules. And it would have a mass of 18g.

Darth Servo · Post by **Darth Servo** » 2003-03-07 11:21pm

kojikun wrote:how many atoms, or how many molecules, etc. one mole of water, for instance, contains 1 mole oxygen and 2 moles hydrogen (every particle of water has two hydrogen, remember)

You take the molecular mass instead of the atomic mass. Then multiply by Avagadros number to get the number of molecules. Then if you want the number of actual atoms, you can multiply by the number of atoms per molecule, in the case of water, 3.

18 g of H2O is one mole.

Post by **Darth Wong** » 2003-03-07 11:37pm

Mad wrote:
Cap'n Hector wrote:Light, as a particle, has mass. It's not much mass, to be sure, but it has a low mass.
Light has no mass. It has momentum, but no mass. If it had mass, then it wouldn't be able to travel at c, as any particle with mass would require infinite energy and mass to travel at lightspeed.

Light does not have mass in the traditional sense, but it has a mass-equivalent. A sufficiently large quantity of pure energy would create gravitational attraction just like a large mass, with a ratio defined by the famous equation E=mc^2.

Shrykull · Post by **Shrykull** » 2003-03-08 12:32am

Darth Wong wrote:
Mad wrote:
Cap'n Hector wrote:Light, as a particle, has mass. It's not much mass, to be sure, but it has a low mass.
Light has no mass. It has momentum, but no mass. If it had mass, then it wouldn't be able to travel at c, as any particle with mass would require infinite energy and mass to travel at lightspeed.
Light does not have mass in the traditional sense, but it has a mass-equivalent. A sufficiently large quantity of pure energy would create gravitational attraction just like a large mass, with a ratio defined by the famous equation E=mc^2.

I'm guessing by pure energy you mean "disembodied energy" energy without regular mass, like photons vs the kinetic energy in a baseball, say you could "roll" a bunch of gamma rays into a ball, it would have gravity?

Kuroneko · Post by **Kuroneko** » 2003-03-13 03:51am

Shrykull wrote:I'm guessing by pure energy you mean "disembodied energy" energy without regular mass, like photons vs the kinetic energy in a baseball, say you could "roll" a bunch of gamma rays into a ball, it would have gravity?

Well... yes. Individual photons contribute gravitational mass; there is even no need to "roll them up" (though of course, their individual effect is negligible).

Darth Wong wrote:Light does not have mass in the traditional sense, but it has a mass-equivalent.

You're correct, but it should be pointed out that the confusion arose from a kind of equivocance. There are two distinct things that are are both called mass--properly distinguished as "rest mass" and "relativistic mass". Most commonly the unqualified term "mass" (in topics where both are accessible--relativity) refers to the former rather than the latter.

Darth Wong wrote:A sufficiently large quantity of pure energy would create gravitational attraction just like a large mass, with a ratio defined by the famous equation E=mc^2.

Perhaps you were too hasty to use the phrase"just like". Parallel (co-directional) light beams do not attract, while antiparallel (parallel, only opposing direction) do so at twice the rate that Newtonian physics would give for their 'mass-equivalents'.

Of course, if photons weren't picky on whether (and how much) to attract depending on direction they're going, any two parallel light beams would eventually collapse into a single one. Luckily, that does not happen.