Gravity, Black Holes and Stars
Discussion
So, gravity. Its a force that keeps you on the ground and stops everything flying off into space, including the atmosphere. it also lets out planet orbit the sun, and our solar system is orbiting a bigger star (or cluster) at the center of the milky way galaxy, which intern orbits a super massive black hole, which will probably orbit something else until you get to a super dupa f
king great big black hole.
we know what it does, but what I cannot get my head around is why?
why does it do what it does. there are a few explanations to that.
molten iron core or earth spinning round really fast and due to mass(?) and spininess it makes us stick to the floor.
but why? why does the iron core spinning cause us to have gravity?
an then we get onto black holes, i understand that when a star has used all of its fuel, that it collapses in on its self because of the super massive gravity field due to burning up all but iron in the 'atmosphere' of the star, then it cannot burn that so the radiation (in form of rads and heat) does not get pumped out balancing out the gravitational force pulling everything it, it turns into a black hole.
but why does the gravity happen in the first place?
that gets me back onto the first point, how, if the last metal elements of the star get compressed soooo small, does it form enough gravity to swallow everything around including light. same goes for a neutron star, how does that have as much gravity as it does, and don't just say because the star's composition is so compressed because of the gravity that is has a greater pull, as thats just going round in a circle.
its not the fact of just having mass creates gravity, and i know there is a measurement of force called dyne, where it is defined as "the force required to accelerate a mass of one gram at a rate of one centimetre per second squared". but does that not need an earth gravity to be a measurement of force?
so ill cut to the chase as i getting quite tired now its late, so, gravity, how does it work, as i cannot get my head around it, and why, when a star dies, does it turn into a black hole rather than a super compressed metal object, as it has no energy to do anything else as it has burnt it up in its lifetime?
king great big black hole.we know what it does, but what I cannot get my head around is why?
why does it do what it does. there are a few explanations to that.
molten iron core or earth spinning round really fast and due to mass(?) and spininess it makes us stick to the floor.
but why? why does the iron core spinning cause us to have gravity?
an then we get onto black holes, i understand that when a star has used all of its fuel, that it collapses in on its self because of the super massive gravity field due to burning up all but iron in the 'atmosphere' of the star, then it cannot burn that so the radiation (in form of rads and heat) does not get pumped out balancing out the gravitational force pulling everything it, it turns into a black hole.
but why does the gravity happen in the first place?
that gets me back onto the first point, how, if the last metal elements of the star get compressed soooo small, does it form enough gravity to swallow everything around including light. same goes for a neutron star, how does that have as much gravity as it does, and don't just say because the star's composition is so compressed because of the gravity that is has a greater pull, as thats just going round in a circle.
its not the fact of just having mass creates gravity, and i know there is a measurement of force called dyne, where it is defined as "the force required to accelerate a mass of one gram at a rate of one centimetre per second squared". but does that not need an earth gravity to be a measurement of force?
so ill cut to the chase as i getting quite tired now its late, so, gravity, how does it work, as i cannot get my head around it, and why, when a star dies, does it turn into a black hole rather than a super compressed metal object, as it has no energy to do anything else as it has burnt it up in its lifetime?
All objects that contain mass (which by definition means "all objects") exert a gravitational pull.
Gravity is purely a property of mass - not a property of the material of which makes up the mass or the behaviour of that material. Whether it is spinning, hot or cold is of minor relevance to gravity. It is the mass that matters.
Isaac Newton defined mass as a kind of attractive force exerted by mass. Nowadays, it is more properly defined as a distortion of "space/time" by the mass of the object. In other words, space/time is bent by the mass of the object and the path of any other object passing by another object will have its path through space "bent" by this space/time distortion.
The presence of iron cores - whether molten, solid, spinning or not-spinning has no real affect on gravity. Indeed, many objects in space have no such cores but still exert gravitational influence - purely because of their mass.
Gravity is purely a property of mass - not a property of the material of which makes up the mass or the behaviour of that material. Whether it is spinning, hot or cold is of minor relevance to gravity. It is the mass that matters.
Isaac Newton defined mass as a kind of attractive force exerted by mass. Nowadays, it is more properly defined as a distortion of "space/time" by the mass of the object. In other words, space/time is bent by the mass of the object and the path of any other object passing by another object will have its path through space "bent" by this space/time distortion.
The presence of iron cores - whether molten, solid, spinning or not-spinning has no real affect on gravity. Indeed, many objects in space have no such cores but still exert gravitational influence - purely because of their mass.
There are a number of fundamental forces that govern interactions between particles and gravity is one of them. Regarding how it works, thats one of the reasons people were pretty excited about the Higgs Boson.
Stars work by a balance between gravity holding it together and radiation pressure pushing it apart - literally the pressure of the particles being created by the nuclear reaction being pushed out of the star. All particles are minutely attracted to others through gravity, (the strength of the attraction being dependant on the distance between the particles) and when you get enough of them the mutual attraction can become so intense that it becomes the dominant force. Thats why atoms and eventually nuclei get crushed together and fusion reactions occur.
The eventual fate of a star will depend on its composition, (mostly hydrogen, but there are some slight variations) and most importantly its mass. If it is heavy enough the gravitational force exceeds the radiation pressure and it collapses into itself and becomes a black hole. Other stars are not so heavy so eventually fizzle out into a variety of other types of 'dead/dying' stars.
Nuclear reactions that basically go from Hydrogen to Helium and onwards can only go as far as Iron in a stable (main sequence) star so anything and everything you see that has an atomic weight higher than Iron has been created in a star that has gone supernova - literally exploded and tore itself apart, (and quite a large volume of space around it - say a radius of 10 to 3000 light years). The conditions for a supernova are rare, but frequent enough and powerful enough to have a profound effect on the universe. We are only here because at least one period of stella evolution has completed - stars have been born, burned brightly for a few billion years or so and then died. We are quite literally as Carl Sagan said, made of star stuff.
Stars work by a balance between gravity holding it together and radiation pressure pushing it apart - literally the pressure of the particles being created by the nuclear reaction being pushed out of the star. All particles are minutely attracted to others through gravity, (the strength of the attraction being dependant on the distance between the particles) and when you get enough of them the mutual attraction can become so intense that it becomes the dominant force. Thats why atoms and eventually nuclei get crushed together and fusion reactions occur.
The eventual fate of a star will depend on its composition, (mostly hydrogen, but there are some slight variations) and most importantly its mass. If it is heavy enough the gravitational force exceeds the radiation pressure and it collapses into itself and becomes a black hole. Other stars are not so heavy so eventually fizzle out into a variety of other types of 'dead/dying' stars.
Nuclear reactions that basically go from Hydrogen to Helium and onwards can only go as far as Iron in a stable (main sequence) star so anything and everything you see that has an atomic weight higher than Iron has been created in a star that has gone supernova - literally exploded and tore itself apart, (and quite a large volume of space around it - say a radius of 10 to 3000 light years). The conditions for a supernova are rare, but frequent enough and powerful enough to have a profound effect on the universe. We are only here because at least one period of stella evolution has completed - stars have been born, burned brightly for a few billion years or so and then died. We are quite literally as Carl Sagan said, made of star stuff.
4G63T said:
its not the fact of just having mass creates gravity
It is, sorry. The best analogy I saw for gravity and space time was - imagine a sheet of material spread tight and place a ball on it. The larger the weight/mass of the ball, the more of an indentation it makes in the sheet/space time, therefore passing things will fall into the depression easier.
In terms of black holes, the concentration of gravity is so large that it has a huge 'indentation' therefore pulling mass towards it and increasing in mass and in turn gravity.
There's other factors here but that's the simplest I can think of to explain it.
Alapeno said:
It is, sorry.
The best analogy I saw for gravity and space time was - imagine a sheet of material spread tight and place a ball on it. The larger the weight/mass of the ball, the more of an indentation it makes in the sheet/space time, therefore passing things will fall into the depression easier.
In terms of black holes, the concentration of gravity is so large that it has a huge 'indentation' therefore pulling mass towards it and increasing in mass and in turn gravity.
There's other factors here but that's the simplest I can think of to explain it.
Good analogy. Gets complicated though when you try to explain gravity waves over Skype to a curious 8 year old nephew using the same tea towel.. The best analogy I saw for gravity and space time was - imagine a sheet of material spread tight and place a ball on it. The larger the weight/mass of the ball, the more of an indentation it makes in the sheet/space time, therefore passing things will fall into the depression easier.
In terms of black holes, the concentration of gravity is so large that it has a huge 'indentation' therefore pulling mass towards it and increasing in mass and in turn gravity.
There's other factors here but that's the simplest I can think of to explain it.
hmm, ok then.
mass it is.
but why, why does something having mass, create a gravitational field? what causes any object to attract other objects?
can anyone explain why does mass create gravity.
i know the thing about a ball on a sheet that has been stretched out making a dip, but where did that example come from?
why does mass cause gravity
mass it is.
but why, why does something having mass, create a gravitational field? what causes any object to attract other objects?
can anyone explain why does mass create gravity.
i know the thing about a ball on a sheet that has been stretched out making a dip, but where did that example come from?
why does mass cause gravity
4G63T said:
....
why does mass cause gravity
One of many unanswerable questions in Science - especially Physics.why does mass cause gravity
Most of us manage to cope with 'what is' and 'how' but not 'why'.
The Universe was not created in such a way as to be easily understandable by humans. It is what it is. (I think Richard Feynman said something to that effect.)
4G63T said:
hmm, ok then.
mass it is.
but why, why does something having mass, create a gravitational field? what causes any object to attract other objects?
can anyone explain why does mass create gravity.
i know the thing about a ball on a sheet that has been stretched out making a dip, but where did that example come from?
why does mass cause gravity
Watch the original Cosmos series if you can as the ball on the sheet experiment is covered well there.mass it is.
but why, why does something having mass, create a gravitational field? what causes any object to attract other objects?
can anyone explain why does mass create gravity.
i know the thing about a ball on a sheet that has been stretched out making a dip, but where did that example come from?
why does mass cause gravity
The best way of looking at it is that mass creates a distortion in space, (the dip in the sheet) which other particles with mass fall into. The reason that this works as an example is because it is a 2D(and a bit) representation of something that happens in 3D, (lets keep time out of it for now). What we understand as 3D space is warped in a way that we cannot visualise because we are restricted to 3D.
Why does matter cause the dip? Well thats a fundamental property of the Higgs particle that answers some of the questions physicists have been scratching their heads about for a while.
All discrete regions of space that have a non-zero value (wave function) in the gravitational field coalesce.
Think of the Matrix, where if you look close enough it's just numbers (This might sound silly but there is a theory that the Universe is not described by Mathematics, it is Mathematics).
These positive numbers want to be next to each other, whereas the zeroes do not. The larger the numbers the more they want be next to other numbers. Nothing really moves through space, the numbers just change in these discrete regions, like waves moving through water.
If the Earth stopped spinning, the gravity would be the same, nothing would go flying off into space (as long as the axial rotation stopped sufficiently slowly), it would just get really f
king hot on one side, and really cold on the other. Until the atmosphere evaporated everyone would want to live in the Twilight Zone. The moon is tidally locked to the Earth in this way, which is why it always looks the same, phases aside. Nobody saw most of the far side of the moon until the Russians sent a probe (Luna 3) around it in 1959. They used to think Mercury was tidally locked to the Sun but it isn't, it rotates three times for every 2 solar orbits, so when it is best placed for observation we always see the same side facing inwards.Make me a car.
At the big bang, when we might as well believe everything was created from nothing in a million millionth of a millisecond. When all this stuff rushed out, there was NO iron to make you a car. There was just Hydrogen, Helium, and a little bit of lithium for hearing aid batteries.
Over a damn long time, agglomerations of this gas formed stars and they were, and still are, the super-forges of the universe. The stars bubbled and heaved and shrunk and sometimes blew up. At their deaths creating the cosmic spray of elements
for the creation of the Ford Escort. Also by the way the constituents for us.
The Solar system was formed from this space crap and Earth has a tutti frutti
composition of it. After some messing about, there are about 100 different ingredients of which every thing is made.
We are going to make a car and we need Iron. (AKA Effie) It is in the dirt of the earth in many places. Three thousand years ago we, mankind, smelt it out. Not with our noses but with furnaces. We forged it and wrought it and cast it and with a bit of a recipe, carbon and air, we make super-iron known as steel.
That's what our car is mainly made of, steel. (We have not disintegrated stars in super novae to make a Reliant Robin.) New steel for our car is now made partly from iron ore and partly from scrap iron, remelted and reused. You have noticed that car scrap yards do not get bigger and bigger. Now and again a tall filthy lorry full of crushed and cut up cars trundles off to start it all off again. Modern smelters use virtually 100% scrap to make new steel, no ore at all. Steel is the most recycled material on Earth.
The interesting speculation is, this procedure having grown this century,
what is in the metal of our car today? Let’s look back, say, four or five recycles......
Last recycle..Ford Escorts, Allegros, Fiat Pandas, Folding shopping bicycles.
Last but one recycles....Hillman Avengers, Sunbeam Rapiers, Citroen 2CV’s
Last but two recycles....Austin Princess, Singer 1500, gasometers. Francis Barnett
motorbike and Cyclemaster motor wheel. The Dome of Discovery
Last but three recycles...Austin 10. Bren Gun Carrier. Morris Commercial lorry.
Steel narrow boat. Levis motorbike. A bedstead from Buckingham Palace.
Last but four recycles... Triumph Gloria. the Battleship Kronprinz Wilhelm, floated
upside down from Scapa Flow by Mr Cox. Brough Superior Motorbike. Sopwith Camel.
Imagine the pots and pans in all this lot, the broken knives, ploughshares, gas pipes, bikes, horseshoes. Mixed as thoroughly as school plasticine. They are all in your car, made from a star.
I will use the analogy of marriage to explain the Strong Force and Weak Force in Atomic Physics. Remember we are talking about atoms and demonstrating their instability. It’s nothing to do with people, and nothing like the real thing, but then analogies never are.
Atoms are kept together by strong force or weak force. Ditto Marriage.
There are more marriages in this World than there are atoms in a grain of salt. This is a proven fact as is everything else hereunder.
Taking this grain of salt. If it had weak force it would be a hangar full of gas instead. As salt we must assume that each contiguous atom is settled and satisfied with its neighbour and therefore hangs in there to go on the chips.
If the nucleus of an atom, which is a negative force and in our analogy will be known as wife, nagged off its positive counterpart (husband) because of its inability to put up shelves, weak force would result and off would come the electron, i.e. husband, to seek compatibility elsewhere, or at least some peace.
The nucleus and electron, you know who I mean, are accidentally conjoined in the first place. Once in this state you would think that all would stay the same, but they are subject to variance.
An initial understanding between them is not possible as attraction overrides all. In proximity before conjunction the electron cannot ascertain that the nucleus will never quite like their house, or the kitchen, or the neighbours much, short of a miracle. If anything is vaguely satisfactory it will be so in a grudging fashion that might as well consign it to the vast carton of what does not suit.
It is this dissatisfaction that creates the weak force, frays and otherwise converts the silk pulse of strong force into the dog-bitten sows ear of weak force.
Once the electron has gone off the nucleus is in imbalance and more dissatisfied than before. Which is not what it desired. It is a mystery of atomic physics that the nucleus cannot link cause and effect. What is proved however is that the free electron is materially depleted, indeed in some cases, it is left with only what he stands up in. Nothing is lost in nature and naturally the Nucleus has gained these particles, known as house, car, money. If by some oversight the electron has gone off with some material attached, say a piece of old sack or half of Hertfordshire, he needn’t think he can get away with that, and indeed he can’t.
The strong force is misnamed in our Atomic analogy I’m afraid. The bond is not the implied trusting hold, but a suspicious grasp. When the dissatisfied nucleus has attenuated it enough, and it is but a weak and dispirited force the partition is quick. ‘Twang’, off goes the electron.
This explains why a particle accelerator the size of the Circle Line is necessary to spot the track of the electron. Drifting can occur but it is more rare, when the weak force is induced by the rare form of mild antipathy by the nucleus, the electron performs what is called the half-hearted, or empty gesture movement. He can be easily followed and brought back.
Well our nucleus, gets the money, but no satisfaction with it of course. The free electron can now look at other nuclei, and very well endowed with the worldly many are too, being the agglomerators in this atomic dance. But an electron can find, by a most odd twist, as yet unexplained by CERN, that the ex-electron can at the same time be despised and also be the paragon by whom all others are measured.
That Nuclei live longer than electrons is false, it is just that the latter die sooner to get out of the laborious task of moving the world a foot to the left. If an electron dies in situ, the nuclei, after getting a cat, are invariably struck with a reverence and respect that was notably absent when he lived and breathed, and our electron would be glad and surprised to know that he is at last satisfactory.
At the big bang, when we might as well believe everything was created from nothing in a million millionth of a millisecond. When all this stuff rushed out, there was NO iron to make you a car. There was just Hydrogen, Helium, and a little bit of lithium for hearing aid batteries.
Over a damn long time, agglomerations of this gas formed stars and they were, and still are, the super-forges of the universe. The stars bubbled and heaved and shrunk and sometimes blew up. At their deaths creating the cosmic spray of elements
for the creation of the Ford Escort. Also by the way the constituents for us.
The Solar system was formed from this space crap and Earth has a tutti frutti
composition of it. After some messing about, there are about 100 different ingredients of which every thing is made.
We are going to make a car and we need Iron. (AKA Effie) It is in the dirt of the earth in many places. Three thousand years ago we, mankind, smelt it out. Not with our noses but with furnaces. We forged it and wrought it and cast it and with a bit of a recipe, carbon and air, we make super-iron known as steel.
That's what our car is mainly made of, steel. (We have not disintegrated stars in super novae to make a Reliant Robin.) New steel for our car is now made partly from iron ore and partly from scrap iron, remelted and reused. You have noticed that car scrap yards do not get bigger and bigger. Now and again a tall filthy lorry full of crushed and cut up cars trundles off to start it all off again. Modern smelters use virtually 100% scrap to make new steel, no ore at all. Steel is the most recycled material on Earth.
The interesting speculation is, this procedure having grown this century,
what is in the metal of our car today? Let’s look back, say, four or five recycles......
Last recycle..Ford Escorts, Allegros, Fiat Pandas, Folding shopping bicycles.
Last but one recycles....Hillman Avengers, Sunbeam Rapiers, Citroen 2CV’s
Last but two recycles....Austin Princess, Singer 1500, gasometers. Francis Barnett
motorbike and Cyclemaster motor wheel. The Dome of Discovery
Last but three recycles...Austin 10. Bren Gun Carrier. Morris Commercial lorry.
Steel narrow boat. Levis motorbike. A bedstead from Buckingham Palace.
Last but four recycles... Triumph Gloria. the Battleship Kronprinz Wilhelm, floated
upside down from Scapa Flow by Mr Cox. Brough Superior Motorbike. Sopwith Camel.
Imagine the pots and pans in all this lot, the broken knives, ploughshares, gas pipes, bikes, horseshoes. Mixed as thoroughly as school plasticine. They are all in your car, made from a star.
- ******* And another one. ***********
I will use the analogy of marriage to explain the Strong Force and Weak Force in Atomic Physics. Remember we are talking about atoms and demonstrating their instability. It’s nothing to do with people, and nothing like the real thing, but then analogies never are.
Atoms are kept together by strong force or weak force. Ditto Marriage.
There are more marriages in this World than there are atoms in a grain of salt. This is a proven fact as is everything else hereunder.
Taking this grain of salt. If it had weak force it would be a hangar full of gas instead. As salt we must assume that each contiguous atom is settled and satisfied with its neighbour and therefore hangs in there to go on the chips.
If the nucleus of an atom, which is a negative force and in our analogy will be known as wife, nagged off its positive counterpart (husband) because of its inability to put up shelves, weak force would result and off would come the electron, i.e. husband, to seek compatibility elsewhere, or at least some peace.
The nucleus and electron, you know who I mean, are accidentally conjoined in the first place. Once in this state you would think that all would stay the same, but they are subject to variance.
An initial understanding between them is not possible as attraction overrides all. In proximity before conjunction the electron cannot ascertain that the nucleus will never quite like their house, or the kitchen, or the neighbours much, short of a miracle. If anything is vaguely satisfactory it will be so in a grudging fashion that might as well consign it to the vast carton of what does not suit.
It is this dissatisfaction that creates the weak force, frays and otherwise converts the silk pulse of strong force into the dog-bitten sows ear of weak force.
Once the electron has gone off the nucleus is in imbalance and more dissatisfied than before. Which is not what it desired. It is a mystery of atomic physics that the nucleus cannot link cause and effect. What is proved however is that the free electron is materially depleted, indeed in some cases, it is left with only what he stands up in. Nothing is lost in nature and naturally the Nucleus has gained these particles, known as house, car, money. If by some oversight the electron has gone off with some material attached, say a piece of old sack or half of Hertfordshire, he needn’t think he can get away with that, and indeed he can’t.
The strong force is misnamed in our Atomic analogy I’m afraid. The bond is not the implied trusting hold, but a suspicious grasp. When the dissatisfied nucleus has attenuated it enough, and it is but a weak and dispirited force the partition is quick. ‘Twang’, off goes the electron.
This explains why a particle accelerator the size of the Circle Line is necessary to spot the track of the electron. Drifting can occur but it is more rare, when the weak force is induced by the rare form of mild antipathy by the nucleus, the electron performs what is called the half-hearted, or empty gesture movement. He can be easily followed and brought back.
Well our nucleus, gets the money, but no satisfaction with it of course. The free electron can now look at other nuclei, and very well endowed with the worldly many are too, being the agglomerators in this atomic dance. But an electron can find, by a most odd twist, as yet unexplained by CERN, that the ex-electron can at the same time be despised and also be the paragon by whom all others are measured.
That Nuclei live longer than electrons is false, it is just that the latter die sooner to get out of the laborious task of moving the world a foot to the left. If an electron dies in situ, the nuclei, after getting a cat, are invariably struck with a reverence and respect that was notably absent when he lived and breathed, and our electron would be glad and surprised to know that he is at last satisfactory.
4G63T said:
i have read that, and I'm going to have to read it it a few more time to understand it properly.
You might struggle, as I have a PhD in physics and I am. He does say "There are more marriages in this World than there are atoms in a grain of salt. This is a proven fact as is everything else hereunder." which might be a hint not to really listen to anything after that point.
4G63T said:
hmm, ok then.
mass it is.
but why, why does something having mass, create a gravitational field? what causes any object to attract other objects?
can anyone explain why does mass create gravity.
i know the thing about a ball on a sheet that has been stretched out making a dip, but where did that example come from?
why does mass cause gravity
In simple terms.mass it is.
but why, why does something having mass, create a gravitational field? what causes any object to attract other objects?
can anyone explain why does mass create gravity.
i know the thing about a ball on a sheet that has been stretched out making a dip, but where did that example come from?
why does mass cause gravity
Mass doesn't create gravity. Mass warps space and time (spacetime)and this warping of spacetime is what we call gravity. The more mass an object has the more it warps spacetime and the stronger the gravitational field. The ball on a sheet analogy stemmed from Einstein's Theory of Relativity where the ball represents an object with mass and the sheet represents spacetime. Although the sheet in this analogy is two dimensional, spacetime is three dimensional but this is just a way of showing it as a visual aid.
As far as we know black holes have infinite mass so this warps spacetime to an infinite amount. The space part has infinite gravity so that not even light can escape the gravitational field and the time part is warped so much that it slows down and at the point of the singularity it stops completely.
Only a few people on the face of the earth can understand the maths involved in this and even they don't fully understand it.
Hope this helps,
Jon
welshjon81 said:
As far as we know black holes have infinite mass so this warps spacetime to an infinite amount. The space part has infinite gravity so that not even light can escape the gravitational field and the time part is warped so much that it slows down and at the point of the singularity it stops completely.
No. Black holes have finite mass, the same mass as whatever collapsed to form them. Think about it - if they had infinite mass, the gravitational attraction towards them would be infinite in magnitude regardless of how far away you were.You are probably confused by the fact that some solutions of the maths for black holes give an infinite density i.e. all of their mass is squashed into zero volume - the singularity. The truth is that nobody knows for sure what's 'really happening' inside their event horizons and we may never know.
hairykrishna said:
No. Black holes have finite mass, the same mass as whatever collapsed to form them. Think about it - if they had infinite mass, the gravitational attraction towards them would be infinite in magnitude regardless of how far away you were.
You are probably confused by the fact that some solutions of the maths for black holes give an infinite density i.e. all of their mass is squashed into zero volume - the singularity. The truth is that nobody knows for sure what's 'really happening' inside their event horizons and we may never know.
Yep, you're right. I worded that wrong and should have stated denisty instead of mass in that sentence.You are probably confused by the fact that some solutions of the maths for black holes give an infinite density i.e. all of their mass is squashed into zero volume - the singularity. The truth is that nobody knows for sure what's 'really happening' inside their event horizons and we may never know.
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