Black Hole, Time Dilation and Redshift

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kewell_

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Ok you guys have probably seen this question a lot but Im gonna go with it anyways.<br /><br />From what I understand, if an outside observer was to witness an astronaut falling into a black hole, relativity dictates that we would see him approach the black hole slower and slower until he ultimately "freezes" in our relative time due to time dilation. My question is, would we actually observe a frozen astronaut in space from our perspective (as in a photographic snapshot)? Doesn't the light become so redshifted that the astronaut's image would appear redder until ultimately fading away? And for the astronaut entering the black hole, would he experience going slower and slower? Curious isf it has effects on his body as well, heart beat etc.
 
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kyle_baron

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<font color="yellow"><br />My question is, would we actually observe a frozen astronaut in space from our perspective (as in a photographic snapshot)?</font><br /><br />Yes<br /><font color="yellow"><br />Doesn't the light become so redshifted that the astronaut's image would appear redder until ultimately fading away?</font><br /><br />Only after a very long time (from our point of view).<br /><font color="yellow"><br />And for the astronaut entering the black hole, would he experience going slower and slower? </font><br /><br />No, he would be falling towards the singularity, rather quickly.<br /><font color="yellow"><br /> Curious isf it has effects on his body as well, heart beat etc. </font><br /><br />He would be torn apart from the tidal forces (spaghtified). OTOH, if he survived and reached the singularity, time will have stopped, along with any motion within his body. <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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weeman

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Kewell_: <font color="yellow"> My question is, would we actually observe a frozen astronaut in space from our perspective (as in a photographic snapshot)? <br /> </font><br /><br />It would take nearly an infinite amount of time for the astronaut's image to disappear across the event horizon. You could watch your friend get closer and closer to the event horizon, yet you will never actually see him cross. He will appear to hang in space just outside the horizon, when in reality, he already crossed into the black hole a long time ago. <br /><br />The reason for this is due to the intense gravity right at the event horizon. Just outside the horizon the gravitational pull is close to the speed of light. Just as your friend crosses over the horizon he will emit his last photons. It will take, what seems like forever, for your friend to appear to disappear into the black hole. <br /><br />Kewell_: <font color="yellow"> And for the astronaut entering the black hole, would he experience going slower and slower? </font><br /><br />kyle_baron: <font color="yellow"> No, he would be falling towards the singularity, rather quickly. <br /> </font><br /><br />Kyle, I think what he meant to ask is whether or not the astronaut would experience time going slower and slower.<br /><br />Is this correct Kewell_?<br /><br />The astronaut traveling towards the event horizon would not notice any difference in his passage of time. Remember that this is the very basis of relativity. Due to his relative frame of reference, he does not notice his clock slowing down. However, as you watch him, if you could somehow see his clock, you would notice his clock slowing down, almost to the point of stopping altogether. In addition, if he could somehow see your clock, he would notice your clock speeding up. <br /><br />The tidal forces of the black hole would not be fun for your friend. The gravity at his feet would be stronger than the gravity at his head, this would cause him to st <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>
 
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origin

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<font color="yellow">From what I understand, if an outside observer was to witness an astronaut falling into a black hole, relativity dictates that we would see him approach the black hole slower and slower until he ultimately "freezes" in our relative time due to time dilation.</font><br /><br />No, this is what you would see; you would see the astronaut faliing into the black hole rather quickly. If he were carring a watch, that you could somehow see, it would be ticking slower and slower the closer he got to the event horizon. His heart would slow and everything about him would be in slow motion but his velocity would not slow down. <br /> <br />Think about it. What people are advocating here is that the closer to the speed of light the slower the time passes which is true but only inside the inertial frame NOT the inertial frame itself. <br /><br />Another way to look at is that you are saying the closer a space ship approaches the speed of light the slower time goes so the slower the space ship goes? So does this mean at 99.999 the speed of light you will only move at a snails pace? Of course not! <div class="Discussion_UserSignature"> </div>
 
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weeman

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Correct.<br /><br />You would see him plunge towards the black hole rather quickly. However, the closer he gets to the event horizon, the longer it takes for his photons to reach you (as an outside observer); thus the reason why it seems to take so long for him to cross the event horizon, even though he crossed it long ago. <br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>
 
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jgreimer

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Don't forget that intense gravitational fields not only dilate time but also contract space. As an object approaches the event horizon it's passing through increasingly contracted space. So what for a far away observer appears to be an object falling through 1 meter of space, for that object it is many meters. Add to that the dilatation of time and the object would seem to slow down as it approaches the event horizon. Suppose an object is falling at 0.9 c, 270 megameters per second. In one microsecond the object feels it has fallen 270 meters. To distance observer it has fallen only 118 meters. Likewise 1 microsecond to the falling object is about 2.3 microseconds for a distance observer. So while the object feels it is falling at 270 megameters per second, to a distant observer it is falling at only 51.3 megameters per second.<br /><br />The best reference I know of can be found here:<br /><br />http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html<br />
 
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