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Thread: The Paradoxical Nature of Black Holes

  1. #1 The Paradoxical Nature of Black Holes 
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    To me black holes represent a paradox within science.

    The thing that is the paradox to me is as follows:

    1. An outside observer watching something fall into a black hole would never see it cross the event horizon.

    2. Black holes evaporate through Hawking radiation.

    Conclusion:
    If you watch something fall into a black hole for long enough the black hole will evaporate before the "something" crosses the event horizon.

    According to theory this is not so. The "something", from it's perspective, would enter the black hole.

    I beg to differ: I submit that if you fell into a black hole (and could survive the tidal forces) that the event horizon would be unreachable as it would fall away from you as you fall towards it.

    For me, the key here is the time warp suggested by theory to exist at the event horizon. It is an infinite time warp to all outside observers and therefore would take an infinite amount of time to traverse. As a black hole evaporates there is not an infinite amount of time available and thus the black hole would cease to exist before you reach the event horizon.

    Personally, I don't think there are black holes and they are a curiosity of general relativity that is holding us back from unifying quantum mechanics and GR. Because we seek to create a quantum black hole the theory will never make sense or be fruitful. We need to move away from this curiosity to unify physics.

    What we think are black holes at the center of galaxies are, in my estimation, something else that we are yet to discover and not until QM and GR are unified.

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    Slinkey


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  3. #2 Re: The Paradoxical Nature of Black Holes 
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    Quote Originally Posted by Slinkey

    I beg to differ: I submit that if you fell into a black hole (and could survive the tidal forces) that the event horizon would be unreachable as it would fall away from you as you fall towards it.
    That makes no sense. Once you're moving on a geodesic bound for the center of the object, you WILL reach the event horizon. In GR, it is the object that accelerates up towards the free-falling object, not accelerate away from it.

    For me, the key here is the time warp suggested by theory to exist at the event horizon. It is an infinite time warp to all outside observers and therefore would take an infinite amount of time to traverse. As a black hole evaporates there is not an infinite amount of time available and thus the black hole would cease to exist before you reach the event horizon.
    No, you would reach and pass the event horizon, however an outside observer would simply see you disappear as the light reflected from you shifts off the scale.

    Personally, I don't think there are black holes and they are a curiosity of general relativity that is holding us back from unifying quantum mechanics and GR. Because we seek to create a quantum black hole the theory will never make sense or be fruitful. We need to move away from this curiosity to unify physics.
    No, GR is NOT holding us back.

    What we think are black holes at the center of galaxies are, in my estimation, something else that we are yet to discover and not until QM and GR are unified.
    Perhaps that may occur, but it does not suggest GR is the problem.


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    That makes no sense. Once you're moving on a geodesic bound for the center of the object, you WILL reach the event horizon. In GR, it is the object that accelerates up towards the free-falling object, not accelerate away from it.
    I couldn't think of another way of saying it but let me try to expland below.

    Let's discuss the event horizon (EH). The EH is not a physical entity. It is the point around a black hole (BH) that marks the spot where time dilation becomes infinite due to gravity. It also marks the spot where any object falling into the BH will be accelerated to light speed.

    According to special relativity when an object is moving relative to yourself it shortens in the direction of its movement. At c the equations of SR imply that an object would have no length at c.

    Now lets translate this to GR. As an object accelerates towards the EH of a BH it would appear to shorten in the direction of its movement. At the EH it would reach c and therefore no longer have any length in the direction of it's movement. But it is not only the object that has shrunk to zero thickness. At this point everything would be shrunk to zero thickness including space.

    How long does it take something of zero thickness to traverse no space? Well, from our perspective at a fixed distance from the EH - forever.

    No, you would reach and pass the event horizon, however an outside observer would simply see you disappear as the light reflected from you shifts off the scale.
    Of course, my argument is not taking this into account light coming from near the EH of a BH will be redshifted (and infinitely redshifted at the EH) so for the purposes of this discussion let's ingore this effect and assume we can see it. Would we ever see it cross the EH? No. It would appear to move towards the EH at an ever decreasing velocity. ie. we would see it getting closer and closer but never see it reach.

    If the black holes is evaporating due to Hawking radiation it will not exist forever. Therefore if we watch long enough we will see the BH evaporate before we see the object cross the EH.

    No, GR is NOT holding us back.
    That's not what I said actually. I am saying that when we try to join GR and QM we try, as one of our tests of our new theories, to create BHs from the new equations. I'm saying that we might be wrong in using this as a test and it could be holding us back. It would be interesting to see theories that do not need to allow for a BH and how close they are to reality.

    Perhaps that may occur, but it does not suggest GR is the problem.
    My perspective is the solutions that allow for black holes may be misleading us.

    On a final and related note let's look at SR again. A spaceship is accelerating at 10m/s^2. When do we see it reach light speed? What about from the perspective of the spaceship?

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  5. #4  
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    Quote Originally Posted by Slinkey

    According to special relativity when an object is moving relative to yourself it shortens in the direction of its movement. At c the equations of SR imply that an object would have no length at c.
    SR is a subset of GR and is not used with accelerated frames, hence your explanation is moot.[/quote]
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    SR is a subset of GR and is not used with accelerated frames, hence your explanation is moot.
    Errr, incorrect. You can do accelerations with SR.

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    Quote Originally Posted by Slinkey
    SR is a subset of GR and is not used with accelerated frames, hence your explanation is moot.
    Errr, incorrect. You can do accelerations with SR.

    cheers
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    But, not when the accelerations are in curved space-time, ONLY flat space-time. Space-time in and around black holes is curved.
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    But, not when the accelerations are in curved space-time, ONLY flat space-time. Space-time in and around black holes is curved.
    Acceleration is curved spacetime. Ref: Einstein.

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    I want to add another thought experiment to this discussion.

    We are hovering at a fixed distance from a BH. We have to accelerate at 1g to stay at this fixed distance. We open the cargo bay door on the underside of our spaceship and drop a clock. The clock accelerates towards the BH under the influence of gravity. After 10 seconds we cut the spaceship's engines and also start accelerating towards the BH directly behind the clock.

    Given that no outside observers can see anything cross the EH (and ignoring redshifting of light and tidal forces for now) how can we ever cross the event horizon ourselves?

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    Quote Originally Posted by Slinkey
    But, not when the accelerations are in curved space-time, ONLY flat space-time. Space-time in and around black holes is curved.
    Acceleration is curved spacetime. Ref: Einstein.
    I don't recall Einstein ever saying that acceleration IS curved spacetime.
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    Let's discuss the event horizon (EH). The EH is not a physical entity. It is the point around a black hole (BH) that marks the spot where time dilation becomes infinite due to gravity. It also marks the spot where any object falling into the BH will be accelerated to light speed.
    Huh? Am I missing something here? This isn't correct , is it? As far as I understand it, an EH is nothing more than the distance from the centre of gravity at which the escape velocity is => C. You would not be accelerated to C before you reach it.
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    I don't recall Einstein ever saying that acceleration IS curved spacetime.
    Einstein stated that acceleration is indistinguishable gravity - gravity is acceleration. If I was hovering a foot above the earth's surface I would feel 1g - acceleration due to gravity. This would be indistinguishable from me accelerating my rocket at 1g in a flat spacetime.

    To state that using SR is invalid because it is a subset of GR is like saying the fur of a brown fox is some colour other than brown when it isn't attached to the fox.

    The results of SR are valid within GR otherwise it could not be a subset of GR. You might want to brush up on your set theory. SR is used in the special case of flat spacetime and it shows how acceleration warps flat spacetime. If it did not there would be no effect.

    If I was accelerating across space I would be able to detect effects and these effects would be due to my acceleration.

    If I fell towards a black hole I would be able to detect effects and these effects would be due to my acceleration.

    In both cases the effects would be the same and indistinguishable.

    It is therefore a viable conclusion to state that acceleration is curved spacetime.

    Unless of course you're claiming that SR describes a different effect from GR, or are you claiming they display the same effects but by different means?

    In the meantime you could always address the second thought experiment, or even the first. Or is it that you are ill-equiped to defeat my argument and thus want to discuss quotes of Einstein instead?

    I don't mean to be rude but the best argument I've had back is that SR doesn't apply because it's a subset of GR which is ludicrous.

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    Huh? Am I missing something here? This isn't correct , is it? As far as I understand it, an EH is nothing more than the distance from the centre of gravity at which the escape velocity is => C. You would not be accelerated to C before you reach it.
    You'll get no argument from me as that's what I said. The EH is the point at which you would be accelerated to c.

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  14. #13  
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    Quote Originally Posted by Slinkey
    Huh? Am I missing something here? This isn't correct , is it? As far as I understand it, an EH is nothing more than the distance from the centre of gravity at which the escape velocity is => C. You would not be accelerated to C before you reach it.
    You'll get no argument from me as that's what I said. The EH is the point at which you would be accelerated to c.

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    Ok then. But is that not the only difference between being just over the event horizon, that you could never go back? To be able to accelerate to C, an infinite resultant force needs to apply to an object, which does not exist just on the other side of the EH. The gravitational force would approach infinity as you go nearer to the singularity, but would only reach epic proportions when you are quite close to it, not at the distance of the EH.
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    It is therefore a viable conclusion to state that acceleration is curved spacetime
    I think what Einstein was saying, is that what we know as gravity, is actually acceleration caused by the curvature of space-time. So one could say gravity = acceleration as a result of space-time curvature, but not acceleration = space-time curvature. Kind of like: All apples are fruit, but not all fruit are apples.
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  16. #15  
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    Quote Originally Posted by Slinkey
    I don't recall Einstein ever saying that acceleration IS curved spacetime.
    Einstein stated that acceleration is indistinguishable gravity - gravity is acceleration. If I was hovering a foot above the earth's surface I would feel 1g - acceleration due to gravity. This would be indistinguishable from me accelerating my rocket at 1g in a flat spacetime.
    Ah, so Einstein DID NOT say acceleration IS curved spacetime. That was either a lie or you're just confused.

    To state that using SR is invalid because it is a subset of GR is like saying the fur of a brown fox is some colour other than brown when it isn't attached to the fox.
    More confusion on your part.

    The results of SR are valid within GR otherwise it could not be a subset of GR. You might want to brush up on your set theory. SR is used in the special case of flat spacetime and it shows how acceleration warps flat spacetime. If it did not there would be no effect.
    And here's what I said, but you said I was wrong:

    "But, not when the accelerations are in curved space-time, ONLY flat space-time."

    If I was accelerating across space I would be able to detect effects and these effects would be due to my acceleration.

    If I fell towards a black hole I would be able to detect effects and these effects would be due to my acceleration.

    In both cases the effects would be the same and indistinguishable.

    It is therefore a viable conclusion to state that acceleration is curved spacetime.
    The conclusion is incorrect. Acceleration is curved spacetime ONLY with gravity.

    Unless of course you're claiming that SR describes a different effect from GR, or are you claiming they display the same effects but by different means?

    In the meantime you could always address the second thought experiment, or even the first. Or is it that you are ill-equiped to defeat my argument and thus want to discuss quotes of Einstein instead?

    I don't mean to be rude but the best argument I've had back is that SR doesn't apply because it's a subset of GR which is ludicrous.
    That wasn't the argument. You only use SR by introducing Minkowskian spacetime, ie. FLAT, which doesn't correspond to the spacetime in and around a black hole; ie. CURVED.
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    Ok then. But is that not the only difference between being just over the event horizon, that you could never go back?
    If you have crossed the EH you can't come back. It marks the point where acceleration due to gravity is c.

    To be able to accelerate to C, an infinite resultant force needs to apply to an object, which does not exist just on the other side of the EH.
    Which side? Inside or outside the EH? Outside the EH acceleration is less than c.

    The gravitational force would approach infinity as you go nearer to the singularity, but would only reach epic proportions when you are quite close to it, not at the distance of the EH.
    Which seems kind of strange when you consider that Einstein said nothing with mass can be accelerated to c. Past the EH the implication is that the strength of gravity keeps on increasing which in turn would imply an acceleration greater than c as the EH marks the point where acceleration due to gravity is equal to c.

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    Quote:
    Ok then. But is that not the only difference between being just over the event horizon, that you could never go back?



    If you have crossed the EH you can't come back. It marks the point where acceleration due to gravity is c.
    C is a velocity, not an acceleration. The boundary of the EH is where the escape VELOCITY is C.
    Quote:
    To be able to accelerate to C, an infinite resultant force needs to apply to an object, which does not exist just on the other side of the EH.



    Which side? Inside or outside the EH? Outside the EH acceleration is less than c.
    Just on the inside of the EH the escape velocity is > C. The gravitational force being applied to the object is not infinite.
    Quote:
    The gravitational force would approach infinity as you go nearer to the singularity, but would only reach epic proportions when you are quite close to it, not at the distance of the EH.



    Which seems kind of strange when you consider that Einstein said nothing with mass can be accelerated to c. Past the EH the implication is that the strength of gravity keeps on increasing which in turn would imply an acceleration greater than c as the EH marks the point where acceleration due to gravity is equal to c.
    As you approach the singularity, the resultant force will increase, which in turn would increase the acceleration. But as you get nearer to C, your mass would more markedly increase as well. So you could never reach C, since an infinite resultant force is needed for that to happen. I did not say anywhere that the object would reach C. No offence, but I think you’ve got your definitions wrong.
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    C is a velocity, not an acceleration. The boundary of the EH is where the escape VELOCITY is C
    With respect I never said it was an acceleration. Last time I looked c was defined as the speed of light in vacuo. The escape velocity is the same as saying the point where acceleration due to gravity is c. At the event horizon you would be being accelerated at that rate. But I take on board what you are saying. You don't neccesarily have to be travelling at c at the EH. The resultant force is not neccesarily equal to your velocity.

    This is wandering slightly from the emphasis on my argument however.

    Just on the inside of the EH the escape velocity is > C. The gravitational force being applied to the object is not infinite.
    I agree. However, my point is to an outside observer you would appear to be slowing down the closer you get to the EH. You would appear to slow down to a standstill but would actually still be moving ever closer to the EH but at a decreasing rate (ignoring redshift effects), but would never be seen to cross the EH.

    As you approach the singularity, the resultant force will increase, which in turn would increase the acceleration.......I did not say anywhere that the object would reach C. No offence, but I think you’ve got your definitions wrong.
    I just forgot that you can always be accelerating against the direction of the gravitational pull and you can cross the EH at less than c.

    But as you get nearer to C, your mass would more markedly increase as well. So you could never reach C, since an infinite resultant force is needed for that to happen.
    Here's a question for you with regard to the mass increase. COuld a body be acclerated close to c and it's resultant mass be enough to create a BH from an outside observers point of view? Or does the dog chase the tail there?

    Could it be the increase in mass that we see in an accelerated body that accounts for the time and spatial effects we observe?

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    With respect I never said it was an acceleration. Last time I looked c was defined as the speed of light in vacuo. The escape velocity is the same as saying the point where acceleration due to gravity is c. At the event horizon you would be being accelerated at that rate. But I take on board what you are saying. You don't neccesarily have to be travelling at c at the EH. The resultant force is not neccesarily equal to your velocity.
    I think the problem with your statements regarding "acceleration (due to gravity) is C" is a semantic one and not one of a lack of understanding. From that sentence, you are saying that acceleration IS C at the EH. What I think you mean to say, is that the force exerted by gravity on a body at the EH, would stop it from crossing the EH back into normal space, if the speed of the object relative to the singularity is =< than C.
    COuld a body be acclerated close to c and it's resultant mass be enough to create a BH from an outside observers point of view?
    Interesting thought, although I think the force necessary for the increase in mass of an object to create a black hole, is only possible inside the EH and very close to the singularity, so it would not be observable to the outside observer. That might be how the mass of the object is added to the singularity itself, with the two singularities merely merging.
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    Sorry been doing nights shifts and haven't had time to reply.

    What I think you mean to say, is that the force exerted by gravity on a body at the EH, would stop it from crossing the EH back into normal space, if the speed of the object relative to the singularity is =< than C.
    Indeed. However, this is moving farther away from my original statements.

    Interesting thought, although I think the force necessary for the increase in mass of an object to create a black hole, is only possible inside the EH and very close to the singularity, so it would not be observable to the outside observer.
    You can accelerate a body to near c with a continued acceleration of 10ms^2. Granted it would take a long time and a lot of fuel but it could be done. That is of course ignoring the fact that the temperature of the background radiation of the universe would be raised traumatically (not to mention deadly micrometeorites) and your ship would be fried.

    But let's use thought experiments to get around the harsh realities. What I want to discuss are the underlying claims.

    That might be how the mass of the object is added to the singularity itself, with the two singularities merely merging.
    If black holes exist that is.
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    I'm gonna reiterate this thought experiment. Anyone care to address it?

    We are hovering at a fixed distance from a BH. We have to accelerate at 1g to stay at this fixed distance. We open the cargo bay door on the underside of our spaceship and drop a clock. The clock accelerates towards the BH under the influence of gravity. After 10 seconds we cut the spaceship's engines and also start accelerating towards the BH directly behind the clock.

    Given that no outside observers can see anything cross the EH (and ignoring redshifting of light and tidal forces for now) how can we ever cross the event horizon ourselves?
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    I'd imagine that close to the EH, we would no longer see the clock, as its light has been stretched too long. As far as the spaceship goes, I don't think you would even notice passing the EH. Especially if there are no x-rays being produced by plasma surrounding the EH. Light inside the spaceship might behave a little differently, to not detectible when reflected directly in the opposite direction of the black hole, less and less shifted to red as it is angled more and more, to gamma rays in the direction of the BH. We in the spaceship would still be free falling, maybe noticing the Doppler effect becoming more and more severe as you near the singularity. The gamma rays might even fry us from the back!
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    I'd imagine that close to the EH, we would no longer see the clock, as its light has been stretched too long.
    We are ignoring these effects for the purposes of this thought experiment.

    We would notice that the clock is slowing down. The clock is accelerating away from us and falling deeper into the gravity well of the BH, but we cannot see it cross the EH.

    As far as the spaceship goes, I don't think you would even notice passing the EH.
    You haven't seen the clock cross the EH yet and you are still behind it in relation to the BH.

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    Going back to the idea of whether an accelerated body could gain enough relative mass to become a black hole. Some things to consider are:

    Imagine the body is a square box with sides of 10m each, ie. a volume of 1000m^3 and a mass of 1000kg. Density of 1kg per 1m^3.

    At 0.8c (for example) the box would would be "squashed" in the direction of it's movement from an outsiders perspective. It would only be 60% as long as it was at rest. Therefore it's volume would now be 6m X 10m X 10m or 600 m^2. It's mass however would have increased 1.666 times and would now have a density of 2.776 kg per 1m^3.

    As the object gets nearer to c this would increase dramatically.

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    Ah, so Einstein DID NOT say acceleration IS curved spacetime. That was either a lie or you're just confused.
    I didn't say he said it else I would've used quotation marks and attributed the quote to him. I said refer to Einstein (ref: Einstein). ie. his theories. There is no lie and no confusion.

    Quote:
    To state that using SR is invalid because it is a subset of GR is like saying the fur of a brown fox is some colour other than brown when it isn't attached to the fox.

    More confusion on your part.
    No confusion here at all. You seem to be claiming that if something moves it doesn't shorten in the direction of it's movement relative to outside observers. It doesn't matter where the force is coming from to make something move relative to yourself. It will shorten in the direction of it's movement regardless of whether the force is a rocket booster or gravity.

    And, as I was talking about an outside observer watching an object fall into a black hole it would shorten in the direction of its movement.

    The conclusion is incorrect. Acceleration is curved spacetime ONLY with gravity.
    We'll have to agree to differ here. I see no difference in the two. They both warp (curve) spacetime.


    Quote:
    The results of SR are valid within GR otherwise it could not be a subset of GR. You might want to brush up on your set theory. SR is used in the special case of flat spacetime and it shows how acceleration warps flat spacetime. If it did not there would be no effect.

    And here's what I said, but you said I was wrong:

    "But, not when the accelerations are in curved space-time, ONLY flat space-time."
    Sigh, for the want of a missed word.

    SR alone is used in the special case of flat spacetime and it shows how acceleration warps flat spacetime. If it did not there would be no effect.

    That wasn't the argument. You only use SR by introducing Minkowskian spacetime, ie. FLAT, which doesn't correspond to the spacetime in and around a black hole; ie. CURVED.
    Indeed that wasn't the argeument. Refer to the first post of this thread and maybe this time you'd like to address the two premises and the conlcusion because thus far you've completely ignored them. My suspicion is that you can't dismantle the argument.

    Movement within a flat spacetime causes that spacetime to warp. Deal with it.

    cheers
    Slinkey
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  27. #26  
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    I always wondered about black holes. I read up on them a couple of times. A lot of planets, stars, dust, etch falls into the black hole, but a fraction of it is ejected from it as a stream of dust and hot plasma. Where do you think the rest of the cosmic dust goes? I remember being told in class that energy can not be created without taking away and can not be completely destroyed only changes form. If this also applies to material objects; why does the black hole completely ignore this?

    I always wondered what happens at the event horizon. Does time fluctuate? Could an object be suspended in time near the event horizon while time flows normally for us? A lot of answers could lie in research of the black holes, because they are considered one of the most destructive but yet the most defying to Law of Physics celestial body in the universe.

    One of the scariest thoughts that science have put out there is, that the center of the galaxy is a massive black hole. How close is our little solar system to the center of the black hole? Could the black hole attract another galaxy unforeseen to us that would upset the orbits of our planets, masked by the Milky Way itself?

    So many questions, possibilities, and maybe technology could be developed by mimic some of the most useful abilities of the black hole. I don’t know, but I feel black holes are worth looking into and studing.
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  28. #27  
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    *sigh* i didn't undersand half of that. i relly need to read up on my physics
    abarat is the best book ever
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  29. #28 Relativisitic Mass 
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    Please ignore anything I said to do with relativistic mass. My statements with regard to it are based on an incorrect understanding.
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  30. #29  
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    Quote Originally Posted by Phox
    One of the scariest thoughts that science have put out there is, that the center of the galaxy is a massive black hole. How close is our little solar system to the center of the black hole? Could the black hole attract another galaxy unforeseen to us that would upset the orbits of our planets, masked by the Milky Way itself?

    So many questions, possibilities, and maybe technology could be developed by mimic some of the most useful abilities of the black hole. I don't know, but I feel black holes are worth looking into and studing.
    If they exist in reality that is. Personally, I think that without a workable theory for quantum gravity the existence of black holes is a moot subject. Yes, astronomers have detected massive objects at the center of galaxies that seem to fall within the required parameters but that in itself is not a proof of black holes. It may be nothing more than circumstantial evidence. At this time I think the best we can say is there are supermassive objects at the center of galaxies. What they are is still open to interpretation as there is nothing in the evidence that says irrefutably this is a black hole as (incompletely) described by GR.

    To allay your fears slightly consider this: if we replaced the sun with a black hole of equal mass to the sun there would be no change to the solar system (except that there would be no sunlight obviously). The planets would continue in their orbits.

    There is plenty of evidence of galactic collisions available and even some very good photographs from Hubble of these collisions. Yes, they cause a lot of changes within the affected galaxies but the time scales for these collisions are far in excess of human life times and thus we really have nothing to worry about.
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