I'm really too tired to read that big paragraph, but I just remembered something from the science class I'm taking right now. For the black hole to absorb light as well, it has to have enough mass for its escape velocity to be greater than the speed of light. At this point light bends into it because its not moving fast enough to escape.
If im wrong there its because we have really old books, although I think thats what the teacher said and not what the book said.
For the black hole to absorb light as well, it has to have enough mass for its escape velocity to be greater than the speed of light. At this point light bends into it because its not moving fast enough to escape. Your problem is you're confusing how it works. The gravitational force on an object is calculated by the following equation G - Gravitational constant m1, m2 - mass of the two objects your testing against r - radius between the two objects' center of mass F = G * m1 * m2 / (r^2) So there really is no limit to the amount of force two objects can exert on each other provided you can get them close enough. However the surface of the star or chunk of mass in question generally prevents you from getting close enough together to get insane enough forces to prevent really fast stuff like light from escaping. If you do some nasty integrals solving for the amount of energy required to get from the surface of the planet/star to infinity then set it equal to the kinetic energy equation and solve for the velocity you get the escape velocity equation which is: v = (2Gm1/r) ^ (1/2) If you substitute v with the speed of light and solve for r you can figure out the point at which it becomes impossible for light to escape. If r is smaller than the radius of the clump of mass then you don't have a black hole since light will hit and reflect off the edge of the surface before it gets to the point of no return. Otherwise if it's larger than this the radius will be the radius of the sphereical volume than you'll see no reflected light from. Also there are no minimum mass requirements for a black hole so if you smashed up something really tiny regardless of what it is you could form a mini black hole. Of course if you don't have enough mass you'll probably have some issues with the nuclear(strong and weak) forces when trying to compact the mass to be dense enough :). There really isn't any magic to it like some people want to believe. Though if you manage to get inside the material making up the black hole you'll experience no force what so ever from it :). | |
Actually, a star with mass enough to become a black hole isn't dense enough to prevent light from escaping it, even if the light started in the middle. Once you pass the surface, everything you've passed starts pulling you back, while everything you haven't pulls you forward. Once a star collapses into a black hole, it becomes a singularity and it'll always pull you in a single direction.
Additionally, one interesting thing to note is that light never actually slows down. It simply appears that way near a black hole because it has to travel further, because spacetime is bent. | |
No, actually, every law of physics is based off of observed phenomena.
Perhaps you are thinking of theories? | |
Actually, a star with mass enough to become a black hole isn't dense enough to prevent light from escaping it, even if the light started in the middle. Once you pass the surface, everything you've passed starts pulling you back, while everything you haven't pulls you forward. Yeah as I noted in another post when you're inside an object it no longer exterts a gravitation pull on you since the mass behind you cancels out the force exterted by the mass in front of you. Once a star collapses into a black hole, it becomes a singularity and it'll always pull you in a single direction. It doesn't have to be a singularity and in fact it probably isn't ever the case since you'd end up with all sorts of problems with infinite forces pushing outward and inward(which wouldn't even necessarily cancel out). And having a resulting outward force of infinite proportions would definitely be bad as you'd have chunks of mass being instantly propelled out to infinity. To have light be unescapable it just has to meet this criteria c < (2Gm1/r) ^ (1/2) I don't feel like doing all the math but if you solve that equation for r you can find the size of the black hole regardless of the density or shape of the mass inside as long as r is larger than the radius of the mass. Additionally, one interesting thing to note is that light never actually slows down. It simply appears that way near a black hole because it has to travel further, because spacetime is bent. This of course is still very theoretical as there isn't any reasonable way as of yet to get any kind of concrete proof on Einstiens special theories of relativity. | |
Theodis, you should be an Earth Science teacher. I understood much more clearly of what you were talking about much better then I did from my Earth Science teacher. And it seems like you sure know your stuff....
P.S. This short paragraph might be worded incorrectly. I typed it extremely, extremely fast cause I gotta' go. | |
As Stephen Hawking once told me, if you took all the heavy hydrogen atoms in the world (or oceans), and turned them into one big hydrogen bomb, the pressure on the matter in the middle of it all would be so much that it would be compressed into a black hole, causing the world (what's left of it) to be sucked in.
(maybe) | |
The point is that physics has no concrete laws. They're often called laws, but they're not. They're just theories.
Archimedes (I think it was him, anyway) thought that a constant force was required to keep an object moving. He pointed out that to push a rock over a flat surface, you have to keep applying force on it. As soon as you stopped applying force, the rock would stop moving. Therefore, he reasoned, the natural state of an object was to be at rest. Newton later reasoned that you actually had to apply a force to stop an object from moving as well, and that it was just as natural for an object to be moving as for it to be at rest. Does this make Archimedes' theory wrong? Well, sort of. Newton's theory is more useful because it encompasses a greater range of situations, but Archimedes' theory was entirely correct based on what he had observed. In that sense, it wasn't wrong. You could say that all of Newton's "laws" of motion are also in a sense wrong, because they don't take into account that time is relative and that space-time is curved by mass. That doesn't make them any less useful as theories. (Ever wonder why games claim to have an accurate Newtonian physics model as opposed to an accurate Einsteinian physics model?) But by no means are they laws. What's my point? Oh, yeah, my point. Right. =) My point is that you can't say "every law of physics is based off of observed phenomena", because there ARE no laws of physics. (It's also dubious grammar, but that's beside the point. =)) When Jon said "laws", he was using the quotation marks for a reason. | |
Have a read of any of these if you like. I don't have time right now to explain it to you myself.
http://www.geocities.com/thesciencefiles/theories/ inscience.html http://www.newton.dep.anl.gov/newton/askasci/1993/biology/ bio086.htm http://www.snopes.com/cgi-bin/ ultimatebb.cgi?ubb=get_topic;f=39;t=000688;p=1 | |
Garthor wrote:
No, actually, every law of physics is based off of observed phenomena.Heh. Bob's Law of Universal Gravitation: Matter tends to move towards other matter. There. A physics "law" that is not based on observed phenomena. I have observed things falling "down", but I haven't observed most things falling towards each other. If I place two pens on my desk a few centimetres apart, they do not just roll towards each other. Also, how does being based off observed phenomena make a so-called "law" not a theory? Theory. noun. : 1. A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena. | |
http://www.geocities.com/thesciencefiles/theories/ inscience.html People like this shouldn't be allowed to post a webpage. In the second paragraph he not only says to completely different things are equal. Then finishes it off with a faulty statement. He gets technically anal on the shape of the earth saying that it isn't really a sphere yet you could counter his truth by just adding more qualifiers. It's like measuring something and saying it's a foot in length only to have someone point out "No it's not it's a foot and 3/32nds of an inch in length!". Then my favorite part :). "Another example of a theory that is not perfect, but is mostly correct, is the simple set of equations that detemine how fast something is moving. This isn't any error in theory it's just this guy being an idiot once again mixing up definitions only to correct himself in the next half of the paragraph. " To find an object's speed, you divide the distance travelled by the time it took. For example, if it is 80 km to the nearest town, and it takes you 1 hour to get there, your average speed was 80 km/h. Now he's got it right by using the correct term average speed rather than speed. " This is so obvious, that most people would consider it to be universally true." Then he goes to start infering that it isn't true when the average is a mathematical term we defined so claiming that it's only a partial truth is just absrud since it contains all the turth it was ever intended to have! This guy seems to have set up an argument and forgot his punchline. It gets more nonsensical in his next paragraph but since he jumps all over the place with his meaning its hard to find his point to critisize. Then he finally gets to the point of the whole thing. "Do you see what we're getting at here? Just because a theory is not 100% correct, does not make it 100% wrong! In fact, most current theories in science that are decades or centuries old are probably mostly correct ... we just haven't finished them yet!" Of course he failed to mention all the theories that are 100% wrong like the ones about maggots being spontaniously created from filth or the good old original ideas on elements. Then I did some digging and found out that it was the science and math section for some high school :P. Which explains why its so bad. Until you get a real education they generally just gloss over topics and give you arm wave proofs since they assume you won't know any better which of course is for the most part right :P. | |
A law is an observation, a theory of an explanation. Thus, a law states "Given X and Y, Z happens," while a theory would state "Z happens because X interacts with Y in W way."
Also, it's not a law if you just make it up on the spot. I'm hoping that you'll put some thought into your next post before making yourself look like a fool. | |
The point is that physics has no concrete laws. They're often called laws, but they're not. They're just theories. There are no absolute truths but if you don't accept some things as fact to base other things off of you won't get anywhere. All your senses are subject to much error and since you have no way to judge them without your senses they could be absolutely wrong. And in the extreme they might not even exist at all since the only thing you can be certain of is that you are concious because if you weren't you wouldn't be able to have that thought :). Laws aren't defined as absolute truths. Generally laws are weel known, have been around for a long while, have many examples of it working, and have no known counter examples. | |
Garthor wrote:
A law is an observation, a theory of an explanation. Thus, a law states "Given X and Y, Z happens," while a theory would state "Z happens because X interacts with Y in W way." Congratulations. You just completely failed to make any meaningful distinction between a law and theory. The two terms are pretty much interchangeable for the most part. Also, it's not a law if you just make it up on the spot. And why not, pray tell? I'm hoping that you'll put some thought into your next post before making yourself look like a fool. Oh the irony! And in response to your entire post - what does any of it have to do with Bob's post? You haven't refuted anything he said, yet you seem to think that you have. | |
Theodis wrote:
http://www.geocities.com/thesciencefiles/theories/ inscience.html I assume you mean "theory" and "theorem". How are those completely different? If you want to get technical (which, ironically, you accuse that webpage of doing below), then yes, they're not exactly the same. The distinction is, however, not worth bothering over when discussing science. Then finishes it off with a faulty statement. He gets technically anal on the shape of the earth saying that it isn't really a sphere yet you could counter his truth by just adding more qualifiers. That's the whole point! The theory that the Earth is a sphere is mostly correct. The theory that it's slightly flattened is slightly more correct. You could continue to describe the Earth's shape in more and more exacting geometrical terms. Does that mean that the Earth isn't a slightly flattened sphere? Of course not. At the macro level, it IS a slightly flattened sphere. There are anomalies, like mountain ranges, but if you're talking on the level of the solar system then those anomalies are so minor that you can ignore them completely. If you're referring to ground level, it's obviously not true; but it's useful to take it as true. If you need more information, you get more detailed. Then my favorite part :). There is an error in the theory. But as I said above, you can discount it for most (though not all) practical purposes, so it's still useful. What definition is he mixing up? There's no faulty definition there. " To find an object's speed, you divide the distance travelled by the time it took. For example, if it is 80 km to the nearest town, and it takes you 1 hour to get there, your average speed was 80 km/h. Geez, come on! You're the only one being "technically anal" here! If people could be crucified for leaving out a word because they didn't want to feel like they were repeating themselves, then we'd all be dead. " This is so obvious, that most people would consider it to be universally true." Congratulations; once again, you COMPLETELY missed the point. Did you even READ the paragraph after that? "What it does not explain properly is motion that is very fast ... at speeds approaching the speed of light." He's not disputing the definition of "average" at all! Then he finally gets to the point of the whole thing. Once again, you are wrong. He did mention incorrect theories. Quote: "For example, a long time ago, most people believed the theory that the earth was flat. This is obviously an incorrect theory." In any case, the paragraph you just quoted doesn't say anything about completely incorrect theories. It only refers to partly incorrect theories. Sigh. People like this shouldn't be allowed to post <s>a webpage</s>. | |
Well, he was right about the Earth not being a perfect sphere. I learned about that in Earth Science (doesn't mean it's right, but saying the Earth is not a perfect sphere even though it looks like one, must mean they did some pretty hefty experiments).
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All of the "laws" of physics and such are just theories. Good theories that have worked so far, but theories none the less. That's a pretty semantic definition, though. For our purposes, laws are unequivocally true. We've never seen them get disproved despite considerable experimentation, ergo, we hold them as proven. Sure, there is no absolute certainty that a ball you let go of will fall to the ground, because we can't fathom the whole of the universe to actually know that the law of gravitation is true... but based on our experiments under ideal conditions, there is a 100% probability that it will occur. | |
Congratulations; once again, you COMPLETELY missed the point. Did you even READ the paragraph after that? "What it does not explain properly is motion that is very fast ... at speeds approaching the speed of light." He's not disputing the definition of "average" at all! Uhh... you said Garthor missed the point. Now you're saying Theodis missed the point? =P | |
(Ever wonder why games claim to have an accurate Newtonian physics model as opposed to an accurate Einsteinian physics model?) Games use Newtonian/Galilean physics for three reasons: 1) Newtonian physics do not hold matter to a speed limit, thereby allowing an object to travel faster than the speed of light. 2) Newtonian physics are simpler, physically possible to simulate, and more appealing to the comprehension of the human brain. 3) Einstein's theories of General Relativity and Special Relativity are widely accepted in the scientific community, but there are still many people who strongly disbelieve in them. In my own opinion, I think the theories of relativity are absolute bull. The theories claim that space time is curved and provide extremely limited experimentation as proof. But I think the experiments are inherently flawed: for example, I feel that it's the acceleration causing the resonance of the particles to deviate, not the velocity. Perhaps the thing that I disagree with the most is the idea that two objects travelling at light speed towards one another are only travelling at light speed in total, and not two times light speed. It defies mathematical logic. While I'm not a mathematical sort, there is one thing I consider to be true, and that's that I believe that mathematical operations can never change. The same operation applied to two different vector or scalar quantities is, in my belief, invariable. 2 * 297,000 km/s is 594,000 km/s, without exception. | |
Well it doesn't need to be infinitely small since the speed of light isn't infinitely fast :). But it does have to be pretty dense. Of course if it were infinitely small you could get within an infintesimal distance and reach a singualrity where you have an infinite amount of force acting on you from an undefined direction luckily though this shouldn't be physically possible.
You're mistaking gravity for escape velocity. The gravitational pull is exactly the same as it was before it collapsed since the amount of mass has not changed and its effect on everything that was nearby it hasn't changed at all. You only start getting to greater forces when you travel beyond what the initial radius of the star was because the force of gravity(like all the other forces) is inversely proportional to the distance between the two objects squared. Since the surface of the object usually prevents you from getting near enough to the center of mass of an object light can freely hit the surface and leave before it gets to this point, but if the object is dense enough this isn't the case. Also if you're within a large gravitational body you experience no gravitational pull from it which also alleviates any extreme forces before a star collapses.