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Black Holes In Question

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anwiii

I didn't bring religion into it other than an example of something that requies faith not evidence.


oh god. are you bringing your crappy talk and pointless arguements in this thread too? you don't have to repeat what i already said that i am not a physisist or a scientist but to go so far as to say i don't even have basic knowledge of science is pretty lame considering everyone who has ever gone through pre college and through college have had to take some forms of science classes. oh but no. we don't know 2 physists like you so that is reason enough to try to say someone doesn't know anything at all about science. i have better things to do than learn the mumbo jumbo. just like programming languages now. doesn't mean i don't have knowledge.

i also stated that i find this thread interesting so i would rather talk to people how i would normally talk. not in nerd talk. i think everyone can learn some interesting theories or possibilities in this thread so to limit people because you say they have no knowledge of science is ridiculous. if someone were to read what you just said, and don't have much knowledge of science, they would be afraid just to enter this conversation because you have stated you wont waste your time with those people here.

and btw- this is the third time you have double posted. stop wasting moderators time by having to merge your posts.

i think you owe a lot of people an appology if you are going to scare them off with your high and mighty talk that you know more and others shouldn't be allowed in this conversation because it would be a waste of YOUR time. i mean you brag about being a teacher but can't even teach in this thread unless someone knows the same or more than you do? get off your high horse pal.

Bikerman

a) I didn't double post.b ) I haven't a clue what you studied, but it wasn't science to anything above nursery level.c) I owe nobody an apology for pointing out that an ignorant person has nothing to say on the matter. If you had asked, rather than pontificated, then I would have been happy to explain.d) Why would I brag about being a teacher? Not exactly a high status job or the sort of thing one brags about.e) It is pointless trying to teach someone who is as opinionated as you are because you don't even know how much you don't know.


anwiii

ummm sorry bud. nursery school doesn't teach science. i studied it in college level but not a lot that had to do with knowing about black holes. you did double post. check again. you like trying to discredit me but it never works. i know you wont appologize. i only said you SHOULD. i said the comment about bragging you are a teacher because you keep talking about your credentials.TRUE! i don't know how much i don't know, but the same goes for you and everyone else. so what was your point in saying that? to just be intentionally offensive to me when it applies to everyone? and why would that dictate that it would be pointless to teach someone that doesn't know how much they don't know? are you trying to scare innocent people away from discussions again because they don't live up to your standards?i wanted to listen and talk about black holes. i didn't say i would agree with anything you had to say. see, i am just an average joe blow on this subject. why would we talk about black holes if we don't know if they exist? isn't it right to talk about if they even exist first? i mean, if they don't exist, what would be the point of even talking about them or having theories about them? i personally am not a believer that they exist, but i wont rule out the possibility since a couple of the theories which explain how they would be formed(if they do exist) make sense to me on my basic level of trying to understand the physics.


Bikerman

ummm sorry bud. nursery school doesn't teach science. i studied it in college level but not a lot that had to do with knowing about black holes. you did double post. check again. you like trying to discredit me but it never works. i know you wont appologize. i only said you SHOULD. i said the comment about bragging you are a teacher because you keep talking about your credentials.

I have never mentioned my credentials, and the references to being a teacher are in context of explaining a wider point, not bragging., as is again obvious when you read the postings.

TRUE! i don't know how much i don't know, but the same goes for you and everyone else. so what was your point in saying that? to just be intentionally offensive to me when it applies to everyone?

No, to point out that you share an unfortunately common fallacy with many others - the fallacy that science should be explicable to people without basic maths. Physics is not explicable without such maths for the reason that you illustrated earlier - 'normal' language is ambiguous and imprecise - that goes for ALL language except the one scientists actually use - mathematics. It is the only language we have with the necessary syntax and conceptual framework to frame the questions and understand the answers. If there is an ultimate designer, the language he/she uses is maths.
So when you ask can the existence of a Black Hole be proved (in fact it would be nice if you had actually asked, rather than assert that it cannot) then you don't have the equipment/understanding to even understand the question properly. That is why I took the time to explain how basic science works and why the notion of proof is not applicable. But your response was that you don't want to understand. Let's see, wow did you put it ?

nor will i ever try to understand them or talk like one. i am just not them. in fact, there are more important things in life than technical mumbo jumbo that explains absolutely nothing and proves absolutely nothing.

And there you sum-up the reason why you will learn nothing about physics.

and why would that dictate that it would be pointless to teach someone that doesn't know how much they don't know? are you trying to scare innocent people away from discussions again because they don't live up to your standards?

No, simply point out that people with delusions of adequacy, who think that mathematics is 'mumbo jumbo', have absolutely no chance of understanding the subject or understanding any answers they might be given. They might get a hazy and very imperfect hint about the science, but it is nursery level science.

i wanted to listen and talk about black holes. i didn't say i would agree with anything you had to say. see, i am just an average joe blow on this subject. why would we talk about black holes if we don't know if they exist? isn't it right to talk about if they even exist first? i mean, if they don't exist, what would be the point of even talking about them or having theories about them? i personally am not a believer that they exist, but i wont rule out the possibility since a couple of the theories which explain how they would be formed(if they do exist) make sense to me on my basic level of trying to understand the physics.

But as I said it doesn't really matter what you believe or don't believe since that belief is based on ignorance. Beliefs based on ignorance are, as I said in another thread, not worth a candle.
You expect the way the universe operates to be comprehensible to you, which is astonishingly presumptuous. You compound that by saying that the language used to frame the questions is mumbo-jumbo. You remind me of a stereotype of my own countrymen when travelling abroad. When confronted by a language they don't understand, they continue to speak English, but LOUDLY and s l o w l y, under the impression that the fault is with the foreigner for not understanding English, and completely oblivious to the fact that the fault is their own.

If you want to understand physics then learn the language. If you are content to have a brief overview explained in non-mathematical terms then fine, but don't criticise the account for being ambiguous and don't think it means you actually understand the concepts because you don't. What you believe is up to you, and matters not one jot. So when you pontificate about 'not ruling out the possibility', you should realise that you sound ridiculously pompous. YOU are not ruling out the possibility. Whoopie do. So what?

anwiii

you sure HAVE mentioned your creditials. not once, but several times. that to me is bragging. just to enlighten you. once is enough. people heard you the first time. ok?

who cares what scientists use. i am not a scientist. are you? i could care less if you know two physicists. if you actually knew what you were talking about, or could come up with something original, you'd be working in that field. don't talk to me about how science is is only explicable to those with basic math skills. science is a lot more than just physics and math and can be explained quite well to others without a WIT of math skills. fortunately, i DO have math skills. but does that enable me to know the physics behind all science? absolutely NOT. again, i do not care what scientist use to determine things. i am not an expert in that field so i will leave it up to those experts.

i never asked if the existance of a black hole can be proven. again, you are misunderstanding for some reason. my english is not that hard to understand. what i said was, SHOW evidence that a black hole exists. it was a statement. i want to be shown how a black hole exists. they say there is one in the middle of our galaxy but fail to even know where it is. this was the basis of my statement because i do not know how one can determine if there is a black hole in our galaxy if they can't even determine where it is. i do want to understand how the basic science works around proving if a black hole exists. what i DON'T want to understand is all the mumbo jumbo. i don't need to understand it. all i need is for someone to explain so i can research what is being said further. since i am not sure weather black holes exist or not, i like to take in all information and come up with my own conclusion whether i believe they exist or not.

so now it doesn't matter what i believe? now i am ignorant? hmmm. that's nice coming from a teacher. i wonder why your students are in your classroom to begin with. do you call them ignorant? do you tell them that their beliefs don't matter either? some teacher you are... your true colors come out in every thread you post in. can you please tell me what school you teach at so i can forward all the threads you replied to to them and allow them to determine if you are qualified to teach? if you don't tell me, i understand. i know you would be afraid of being found out....

i don't expect the universe to be comprehensible to me. did i imply that at all? no i did not. if i did, please state a direct qoute. again, you are confused with basic english when i stated clearly already that all i wanted to know more about are black holes, the theories and the possibilities. i will NEVER expect to understand the universe. i have a hard enough time understanding people and the deeper side of life. it's a rewarding challenge.

i stated that scientist use a bunch of mumbo jumbo to explain things. i think they try to be more technical than they have to be. how is it anyones fault if two people don't understand eachothers language? even though i think you are very technical in the language you choose to speak, i never critisized it once. if that is your way of speaking to people, then by all means, speak it that way. but if i don't understand something you said, then i wont hesitiate to tell you even if you are confused by my confusion. you have friends who go to other countries and speak like retards? loud and slow? what does that have to do with anything? you are comparing your friends to me because i am speaking a foreign language? hmmm

again, i do not want to better understand physics than i already do. there is no need for me to waste my time on a language i will never use in my every day life. what i believe and know is more than you will ever know about me. unlike you, i don't go bragging about my credetials when i am talking to someone. have you seen me do this when i am talking to you? no. you have done it several times like it should mean something. well i don't do it because it doesn't mean jack. i have known many people who seem to know alot because they read a bunch of books, but in actuality, know very little because they have little experience outside of their books.

so now let me give you one of my basic philosophies in life. if you aren't making mistakes, you aren't living. it's how we learn. i will be the first to admit i am a dummy. i always have been, but i will tell you one thing. i learn from my mistakes. by doing that i become more knowledgable and wiser. not be learning. by DOING and by QUESTIONING even if i am a dummy in the area in question. now if you have a problem with that or how i choose to live my own life, then that is ok. no skin off my back, but i will have to always disagree with you when you start making false assumtions in things you know abosultely nothing about. i will call you on it every time with your foot in your mouth only making you look stupid until you wise up and admit YOU don't know it all to say half the things you have said recently.

i sound ridiculous and pomous? to you maybe. to some others....maybe that is true too. at least i don't go starting arguements in every thread i am in and disrespect other peoples beliefs and opinions and questions. so again....maybe you should look in the mirror before judging others because again.....i think you are the pot calling the kettle black and i think you are in denial.

my beliefs in black holes or science may not matter one bit, i agree. i am not out to influence science or make a name for myself by coming up with a new theory. but are you? are you going to do anything but cite what you read or are you ever going to come up with something original? maybe whatever your belief in science is not worth a jot if all you are going to do is copy other peoples work for your own beliefs. there is a name for that. it's called a follower. a word i use to describe people who follow any specific religion and live by the rules that religion dictates. in some ways, science is a religion in and of itself....instilling strong beliefs in theories and hypothesES.

YOU are not ruling out the possibility. Whoopie do. So what?

you are REALLY a muture teacher, you know that? are the words "whooptie do" something you say when you cleary don't have the words to explain yourself because you are just utterly confused in how to communicate properly?

Bikerman

Again a mass of problems.

a) Misunderstanding.

you sure HAVE mentioned your creditials. not once, but several times.

If I have mentioned my credentials then please tell me what they are? What degrees do I have and from where? What postgrad training have I done and what recognised qualifications do I have outside my degrees?

A credential is an attestation of qualification, competence, or authority issued to an individual by a third party

b ) Contradiction.

i do want to understand how the basic science works around proving if a black hole exists.

i do not want to better understand physics than i already do.

The basic science IS physics.
c) Misconception.

science is a lot more than just physics and math and can be explained quite well to others without a WIT of math skills.

No, it can't. It can be analogised but analogy isn't the same as the thing being analogised. We can say 'it is like....' for some things, but all analogies break down eventually and most of physics isn't 'like' anything a human would have perceptual experience of. If I say an atom is like a miniature solar system then that gives a rudimentary picture but it doesn't give any real understanding and it is useless as a predictive model. If I say a black hole has a singularity then it means nothing because you have no reference model to compare it to.
d) Logical contradiction:

they say there is one in the middle of our galaxy but fail to even know where it is.

e) Red herring fallacy:

how is it anyones fault if two people don't understand eachothers language?

It isn't but that is not relevant since here we are talking about YOU not knowing the language of the question you ask. It isn't a case of physicists not knowing your language - I know plenty who speak great English. The fault, to the extent it is anyones, is yours.
f) Ad-hominem.

can you please tell me what school you teach at so i can forward all the threads you replied to to them and allow them to determine if you are qualified to teach?

No, they have enough cranks to deal with already without me pointing more at them. A bit of research should find me easily enough, I don't make any special efforts to conceal my identity on the web.
g) Lie.

i never asked if the existance of a black hole can be proven.

please give me resources that prove they exist and who proved it.


anwiii

what exactly does any of what you just said have to do with black holes? see not only have you bragged about a teacher several times like it supposed to mean something, but you told me specifically you are a moderator or used to be a moderator on more than one forum when you kept breaking the rules here quoting things without using quote tags, double posting, and now not speaking on topic. what does being a moderator on different forums mean if you can't even follow the rules of the forums you are in? as a moderator you should know better. as someone who has the credentials you brag about, you should know better. someone with any little bit of common sense should know better. just because you think you're better than everyone else doesn't meant he rules don't apply to you. every topic you are in, you portray a person you are talking to as a lower class person compared to yourself. but again, what does your last post have to do with black holes? or are you going to continue repeating yourself that since i don't know physics as much as certain experts do, i shouldn't have a voice here? i keep asking you what gives you the right to tell anyone that they cannot post their opinions and beliefs without those people being shot down as to not knowing anything? what gives you that right? what gives you the right to destroy someone elses topic that they started because they were interested in the theory of black holes just like i am? and even interested in coming up with theories of our own even if we aren't qualified under your standards? who is qualified to speak here about black holes, bikerman? you and bani only because you both showed an interest in physics? gimme a break.

there is no misunderstanding. you keep bragging about your credentials. you even did it in private pm with me. i am not going to go re read everything you said just to list everything you keep bragging about. that is stupid to even ask when you know you have been doing exactly what i have stated. i am not going to waste my time while you play stupid.

contradiction? there is no contradiction except for your own misconceptions. physics is NOT basic science! haha physics can be said to be a fundamental science but it doesn't define science! that statement you made is preposterous coming from a teacher. i really hope you aren't a science teacher.

you don't have to explain psychics to me. i took it in college. it was(in my opinion)one of my favorite classes. and plus, i think you just like to make up things as you go along....

if i post something irrelevant, who cares? i am not trying to debate anything with anyone even though you want to try and string me along to create an arguement. personally, i think a lot of what YOU say is irrelevant to to topic at hand in regards to black holes. instead of trying to discredit me, why don't you try to answer my basics thoughts on black holes instead of giviving everyone the run around as you are VERY good at doing with your mumbo jumbo.

it doesn't surprise me that you would want to try and hide the threads you post in here from the people who hired you as a teacher. i said from the start that i knew you would be afraid if the truth got out in who you really are. it's good to be in agreement on this. anyway, i already know you work at river*... so it's not like you would be telling me something i don't already know. again, i think the staff there will be VERY interested in how you are possibly teaching our future generation. but if you are not going to confirm, can you please confirm which forums you are a moderator on or have moderated? i want to verify that information too. but anyway, i know a lot about you. more than you probably want me to know. this is why i can accurately talk about you without being ignorant(as you would call me)

i never asked if the existence of a black hole can be proven.

that wasn't a lie.....

please give me resources that prove they exist and who proved it.

please tell me if you saw me ask a question in that last quote. was there a question mark? what i said was in form of a STATEMENT made. not a question. there is a HUGE difference but i am so glad you made it very easy for me to disprove you as a teacher once again and as a person here in the forum who tries so desperately to hide his ignorance and confusion. those two quotes were actually directed at bani, not you....so why are you even quoting me(and then misquoting me) as if i were talking to YOU?

now that i have adhered to your misc. and irrelevant babble, can we NOW get back to the discussion of black holes even if you don't like the way that *I* like to talk about them? your arguments against me are pointless and serve no purpose except to stop talking about black holes entirely.

Bikerman

Here's some observational evidence for black holes:

Posted Image

This is a Hubble image of galaxy NGC4261.

The white outer part is the stars in the centre of the galaxy. The brown disk in the middle is thought to be a Supermassive Black Hole.

How do we know? Well, like most galaxies this one is rotating around the centre. The only thing stopping the stars carrying on in a straight line, and thus flying apart from the galaxy, is the gravity at the centre pulling the stars inwards.

By observing a few stars over a period of some months it is possible to work out how fast they are rotating around the centre. From that we can calculate the gravity or the mass at the centre.

In this case the calculation shows that the centre must have a mass of 1.2 billion solar masses (1.2 billion times as massive as our sun), but it is only about the size of our solar system. When we plug these figures into a standard calculation, then we get a gravity of about 10^6 (1 million) times that of our sun. No matter can stand-up under that much pressure*.

 

Other observational evidence for black holes:

Posted Image

 

This shows an image from Hubble showing galaxy M87. You can see the spiral-shaped object highlighted. Again this was 'weighed' using rotation speed and found to have a mass 3 billion solar masses. The object isn't black because of the filters used to capture the image - it is black without them.

 

* As you pack matter together first it reaches a limit called the electron degeneracy limit. This is where the electrons around the atoms cannot be compressed anymore. The limit is set by Pauli's exclusion principle that states two fermions cannot occupy the same 'space' at the same time. As they are pulled harder and harder then the only way for an elecron to avoid being in the same place as another is to jump to the next quantum level around the nucleus. The pressure needed to overcome this can be calculated fairly simply - but you won't understand the calculation so you will just have to take my word for it. If the pressure (or gravitational pull) is higher than the electron degeneracy number, the mass marries on collapsing until there is just basically a gas of neutrons (the electrons combine with protons to form more neutrons) and the end result is a neutron star. Neutron stars form when a star 1.4 times the mass of our sun (or larger) 'dies' (ie it runs out of fusable hydrogen, fuses the helium, runs out of helium and fusion stops. At this point there is nothing 'pushing' against the gravitation of the star and it begins to collapse in on itself).

 

Next limit is the neutron degeneracy limit/number. This is a similar limit, but higher, since the force inside the nucleus, binding the protons and neutrons together, as well as binding quarks and gluons into protons and neutrons (the colour force) is stronger (100 times) than the force binding the electrons to the nucleus (the electromagnetic force).

Even so this has a limit and once the pressure/gravity passes that limit then the mass continues to collapse, the neutrons become 'degenerate' and we get a black hole.

There is one theoretical stage between the electron and neutron degeneracy - the quark degeneracy stage, but little is known about that because experimenting on quarks isn't possible (you need more energy to pull quarks apart than it is possible to generate, because colour force binding them together actually gets larger as the distance increases (unlike all the other forces).

 

So if the star is massive enough to overcome electron, neutron (and quark) degeneracy limits then nothing can hold the mass together and the entire mass of the star becomes 'degenerate' and since there is nothing keeping the neutrons collapsing into each other the process continues until we have a singularity.

 

A singularity is a hypothetical 'point' which has no length, breadth or width (ie no spatial extent at all). We cannot see a singularity because the gravity is so intense that a boundary is created as a sphere surrounding the singularity - the Event Horizon - and within that boundary gravity is large enough to stop anything escaping, including photons (light).

 

That is a black hole.


anwiii

great! that is what i am talking about. i like that detailed information and it's good to get back on track here.ok. so from this, we should all assume that black holes exist? i have read similar things in the past, but i am still not totally convinced that what you wrote about is a "black hole". sure, a black hole is defined and what we have observed in the past in following stars, and the gases or the light illuminating from the gases disappearing in blackness sort of goes along with the theory of what a black hole is, but we are only taking one scenario to say that this is proof?even YOU said that science tends to disprove rather than prove. but i didn't agree totally with that statement either since i know that science CAN prove things beyond a reasonable doubt over time. i say reasonable doubt because i do believe nature is unpredictable at times(the universe being part of nature in my definition) and science will never have the ability to prove everything.... just disprove SOME things.i am too tired to think right now. i will have to continue tomorrow. i just don't understand why light that "should" illuminate after a period of time, means that whatever was illuminated, entered a "black hole". i understand how a star can implode and create a gravitational pull. what i DONT understand is how something can become nothing unless the energy of that something is transformed making the original energy look like nothing.now again, i may be ignorant in this area, but i do like to exersize my simple mind once in a while....i am also curious about black holes in the sense of their density and mass. i think obviously, the more denser and massive, the more gravitational pull. but when something is so dense, how would one ever reach the center? if something was that dense and so massive that nothing can escape it, then it would be safe to assume that a black hole GROWS....yet there are theories that say black holes get smaller. if both are true, what is the final outcome of a black hole then? what does it leave behind? or does a black hole just recreate itself by imploding again just like the star did?anyway, food for thought for this simple mind who has been drinking tonight :) and thank you for allowing us to get back on topic. this topic has always fascinated me.....some of the mysteries of the universe....and what it all means and the purpose behind it....


Bikerman

ok. so from this, we should all assume that black holes exist? i have read similar things in the past, but i am still not totally convinced that what you wrote about is a "black hole". sure, a black hole is defined and what we have observed in the past in following stars, and the gases or the light illuminating from the gases disappearing in blackness sort of goes along with the theory of what a black hole is, but we are only taking one scenario to say that this is proof?

No, I only provided the two because I could get easy pictures. There have (last time I checked) been spectroscopic readings done on 750 plus galaxies and to date every one has shown a similar feature (ie stars in the centre spinning rapidly indicating a massive central black hole. It is now generally thought that all galaxies have a central super-massive black hole and that this is important in their formation.

even YOU said that science tends to disprove rather than prove. but i didn't agree totally with that statement either since i know that science CAN prove things beyond a reasonable doubt over time. i say reasonable doubt because i do believe nature is unpredictable at times(the universe being part of nature in my definition) and science will never have the ability to prove everything.... just disprove SOME things.

 

There are several ways to disprove it. Find a galaxy without a SMBH at the centre - that will disprove the theory that they are at the heart of every galaxy and it will cast doubt on the hypothesis that it is centrally important to galaxy formation

Alternatively find a better explanation for the speed of rotation in the centre of the galaxy.

i am too tired to think right now. i will have to continue tomorrow. i just don't understand why light that "should" illuminate after a period of time, means that whatever was illuminated, entered a "black hole". i understand how a star can implode and create a gravitational pull. what i DONT understand is how something can become nothing unless the energy of that something is transformed making the original energy look like nothing.

 

As material is drawn closer to the event horizon it accelerates rapidly and bumps around with other stuff. These collisions convert the kinetic energy of the 'stuff' into heat and the gas, rocks, plasma etc begins to get hot and starts to glow.

Once the material passes the event horizon then no photons can escape so you cannot see it any more.

If the source of gravity was not a BH then you would see a ring around it - as matter hit the surface of whatever it was then it would give a great burst of energy - like a heavy weight dropped to the ground. This would produce a very hot ring of glowing material all around the surface of the object. That is not what we see in the image....

i am also curious about black holes in the sense of their density and mass. i think obviously, the more denser and massive, the more gravitational pull. but when something is so dense, how would one ever reach the center? if something was that dense and so massive that nothing can escape it, then it would be safe to assume that a black hole GROWS....yet there are theories that say black holes get smaller. if both are true, what is the final outcome of a black hole then? what does it leave behind? or does a black hole just recreate itself by imploding again just like the star did?

 

The mass is the mass of the material before it collapses into the singularity. If we assume a star of 10 solar masses collapses into a BH then (leaving aside the material blown off) you have a BH of 10 solar masses. The mass is all in the singularity which does not grow in size but does get more massive. The density of the singularity, as I explained, is theoretically infinite (density = mass/(4/3pi*r^3) but r=0 so mass/0=?). String theory predicts something different. The truth is that as far as we know you can never see a singularity or approach it - this is known as the cosmic censorship hypothesis.. So it is not sensible to talk about the density of the singularity - but we can talk about the density of the BH just as with any other object. So yes, BHs grow as long as there is mass near enough to feed on. When it has sucked-in everything around then it is dormant.

 

As for getting smaller - A process called Hawking radiation is constantly happening. This is complex and cannot be analogised but I will try.

Virtual particles form all through space, so we get, for example, virtual electron/positron pairs forming continuously, then combining again to annihilate in a puff of energy. When such a pair forms close to the event horizon of a BH then one of the pair may be sucked into the BH and the other escapes. In order to preserve mass-energy (conservation of mass/energy) the new particle that was liberated into the universe must be balanced by a corresponding loss of energy equivalent to that mass - this comes from the BH. The BH therefore loses energy each time this happens, although the energy loss is very small indeed.

(In fact I am told that some recent work by colleagues at Fermi-lab indicates that Hawking's proposed radiation does not apply to larger black holes. If this new hypothesis is correct then any decent sized black hole will not get smaller over time - there will be more cosmic radiation falling into it than it could re-radiate via Hawking radiation.)

 

Black holes can also grow by eating each other. They spiral into each other and the result is a single black hole with the combined mass of the two that go to make it.

Here is a simulation of what might happen in a few billion years when our Milky-way galaxy collides with Andromeda.

 

 

[media]http://forums.xisto.com/no_longer_exists/]

Now, none of this is true, it is all analogy. If you want to really understand what goes on then you need to get into maths. As far as non-maths explanations go this is not bad, if I say so myself, but it is meagre & unexciting to me, and it doesn't get near the beauty of the real descriptions, let alone the accuracy. I cannot describe the symmetries involved, the actual behaviour of matter as it is drawn closer to, then over the event horizon. The probability that a rotating black hole would have another region inside the event horizon where mass/energy slowed below light speed due to the 'centrifugal' force* and so on...

 

* the notion of centrifugal force is actually a very good example. There is no such force and never has been. It is a convenient word, but it doesn't represent anything in reality, since there is no real force pulling the weight in the opposite direction to the string as you twirl it around - it just feels like there is.

This diagram is all wrong, but unless you know the basic maths then it is the best lie we can tell...

Posted Image


zanzibarjones

How can you bring Gravity into this?Can you tell me 100% by what magical circumstance is gravity created and in charge of this?For decades people have said that gravity is created by forces spinning, then it was said that gravity was like a ball on a rubber mat. A bend in space. Now gravity in and around a black hole defies all of that be being sucked into the center of an object?So which is it? Is a black hole using gravity to pull things in, or some other force?If light can not escape a black hole, would you not agree then that gravity has nothing to do with it? Because I don't believe light is affected by gravity."According to Einstein's General Relativity Theory,light will be affected in the same way matter is affected by gravity. This is because under this theory, we should think of gravity not in terms of vector like forces, but as a consequence of the "shape" of the universe."


Bikerman

How can you bring Gravity into this?Can you tell me 100% by what magical circumstance is gravity created and in charge of this?
For decades people have said that gravity is created by forces spinning, then it was said that gravity was like a ball on a rubber mat. A bend in space. Now gravity in and around a black hole defies all of that be being sucked into the center of an object?

So which is it? Is a black hole using gravity to pull things in, or some other force?

If light can not escape a black hole, would you not agree then that gravity has nothing to do with it? Because I don't believe light is affected by gravity.

"According to Einstein's General Relativity Theory,light will be affected in the same way matter is affected by gravity. This is because under this theory, we should think of gravity not in terms of vector like forces, but as a consequence of the "shape" of the universe."

Right - stick with the rubber mat. It isn't perfect but it will do.
There is no 'force' of gravity in relativity. Things move in straight lines, but the straight lines themselves are bent by mass. This is where you drop a weight onto the rubber mat. There is no force acting on a particle that goes past the weight - it is just that its normal straight-line path has a curve in it, so it follows the curve.
Now, curve enough and the particle (small ball is normally used) will go into orbit - spinning around the weight.
Add more and more weight and the rubber stretches with steeper and steeper sides until once the small ball has gone too far, it can never get out, no matter how fast it spins....
This applies to everything - mass AND light - they all follow the curved path.

zanzibarjones

Maybe I'm un-educated, oh wait I am.... I don't understand how light can be affected by this? Light has no mass... can you explain why light follows this rule too? I understand why mass does.By the way I love causing trouble with questions like these :)


Bikerman

Maybe I'm un-educated, oh wait I am.... I don't understand how light can be affected by this? Light has no mass... can you explain why light follows this rule too? I understand why mass does.

OK. Light has no rest mass (ie if you could stop light it would disappear). Now this doesn't matter because in Relativity nothing is 'pulling' the mass. Gravity isn't a force, it is just the bend in spacetime (the rubber mat). Let's simplify it and leave the 'time' bit out and just deal with space.
So the mat is space and the weight is mass causing gravity. Does it matter how much mass the things you roll past the weight have? Yes. Good answer. BUT what if you imagine something with no mass? It will still follow the curved path of the rubber, not an absolute straight line. That is how light is - it follows a path (we call it a 'geodesic') which without any weight distorting the mat is a straight line, but when weight is added the path becomes curved.

Bikerman

If you really want to boil your noggin then try getting to grips with some of the rest of the theory of Relativity. One common source of bafflement is something called the 'Twin's Paradox'.
This is relevent to black holes because extreme gravity causes time dilation - ie different clocks go at different speeds depending on the gravity - and you age at a different rate. Essentially time goes at different rates in different gravity fields.
It also happens when you go very fast. The Global Positioning System has to account for both of these factors - the satellites are wizzing around pretty quick, that means they have a slower time than on the ground. But the gravity is much less up there which speeds their time up again. You have to calculate both effects, subtract one from the other, and then you can make the clocks tick at the correct speed. This is vital because they pulse information down to you at the speed of light (nearly) and by measuring the time, you work out the distance. Even a very small error (0.00001s) would mean you were way out when you calculate the distance, because light travels so quickly.

If you want to try to understand this, the following is a really nice site for novices in Relativity
Click Here


zanzibarjones

If you really want to boil your noggin then try getting to grips with some of the rest of the theory of Relativity. One common source of bafflement is something called the 'Twin's Paradox'.This is relevent to black holes because extreme gravity causes time dilation - ie different clocks go at different speeds depending on the gravity - and you age at a different rate. Essentially time goes at different rates in different gravity fields.
It also happens when you go very fast. The Global Positioning System has to account for both of these factors - the satellites are wizzing around pretty quick, that means they have a slower time than on the ground. But the gravity is much less up there which speeds their time up again. You have to calculate both effects, subtract one from the other, and then you can make the clocks tick at the correct speed. This is vital because they pulse information down to you at the speed of light (nearly) and by measuring the time, you work out the distance. Even a very small error (0.00001s) would mean you were way out when you calculate the distance, because light travels so quickly.

If you want to try to understand this, the following is a really nice site for novices in Relativity
Click Here


Yeah and ya know Stephen Hawking says that if you were able to travel at the near speed of light speed, you would be travelling into the future. The thought that if you could travel at that speed, leave earth and return in what you think is 25 years would actually be 100 years (or somewhere around there). I think that is cheating by saying you've traveled through time. I mean at that speed things slow down. So technically you are just not aging as fast as some who stayed on earth.

I know, white rabbit, sorry. Just had to get that in there. time travelling.... whole different subject.

Bikerman

Yeah and ya know Stephen Hawking says that if you were able to travel at the near speed of light speed, you would be travelling into the future. The thought that if you could travel at that speed, leave earth and return in what you think is 25 years would actually be 100 years (or somewhere around there). I think that is cheating by saying you've traveled through time. I mean at that speed things slow down. So technically you are just not aging as fast as some who stayed on earth.

 

I know, white rabbit, sorry. Just had to get that in there. time travelling.... whole different subject.

 

Well, not really - all part of the same.

 

Why is it cheating? Surely if you can travel for a year and go 20 years into the future (and you can do better than that if you go fast enough) then that must count as time travel?

Yes, you are only slowing the clocks down, but that is still time travel - you are travelling at a different rate in the time dimension.

The way I imagined this to get started is quite a good little mental picture - you might find it useful.

 

You travel in spacetime. Spacetime is space and time all wrapped up into one. Your speed through spacetime is always the same - the speed of light. We spend all our time doing nearly all of that travel through time (we don't move fast enough to really count when it comes to moving through space. The fastest human speed achieved is about 25,000mph in Apollo 10. Compare that to 187,000 miles per second, and you see how slow it is.

 

Since the speed through spacetime is always the same, the faster you move through space, the slower you move through time (although to you it is no different because your life is measured against spacetime, as is everyone else). The difference is only obvious when someone else doesn't move through space as fast as you. They are then moving through time much quicker than you.

 

Get it? It is a handy little mental model to explain what is going on.

 

This is where the maths is useful, and the maths for time dilation is easy peasy - watch and I bet you can follow it no bother.

 

Let V be the speed through space of you. Let V1 be my speed through space. (I need to use velocity rather than speed, because otherwise we might not be moving apart as fast as we are moving - we might be moving at angles to each other).

 

So your velocity is V and mine is V1.

We want to know the speed that our clocks are ticking. Another way of saying that is we want the rate of change of time. Rate of change, in maths, is written as a greek letter Delta (Δ), so the rate that your clock ticks can be written as ΔT and mine can be written as ΔT1. That's all we need. The formula for calculating the different rate is:

ΔT1 = ΔT/(square root(1 - V2/c2)

 

If I has a square root sign that would be perfect. Still, you can see it isn't very hard. The extra term ( c ) stands for the speed of light (our speed through spacetime).(I can actually show you how to get this forumla just using pythagoras and a right triangle, but that is another time).

So you might see from this formula that the important bit is the V2 - your velocity squared (we could swap, it doesn't matter, since this will work whether you are V or V1)

 

As your velocity gets closer to the speed of light - c - then that last bit of the formula gets closer and closer to c2/c2 which is 1. (anything divided by itself is 1). And look what happens then. You get ΔT/sqrt(1-1) in other words ΔT/0 which is not possible - or we can say it is infinite - you cannot divide anything by zero and get a sensible answer. Theoretically, if you could move at the speed of light then no time would pass for you at all. You could fly right round the universe and no time would have elapsed for you. Now you can't, because it isn't only time that goes wacky, length and mass also go wacky and they both use the same formula. So if you use L for length instead of T for time then the forumla is the same. Likewise, use M for mass and the formula is the same. That means as you get close to the speed of light, your mass goes up and up towards infinity and your length gets longer and longer towards infinity. Remember that this is from my viewpoint - you don't feel any change at all. So I see you stretch out in length, I see your clock go slower and s l o w e r and I see you getting heavier and heavier (or I would, if i could weigh you).

 

See, it's much better with the maths ;)



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