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<table border="0" cellpadding="0" cellspacing="1" width="95%" align="center"> <tr bgcolor="#234c6f"><td> <table border="0" width="100%" cellpadding="4" cellspacing="1"> <tr bgcolor="#234c6f"> <td colspan="2" align="left"> <font size="3" color="#FFFFFF" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>T O P I C ��� R E V I E W</b> </font></td></tr> <tr bgcolor="#A3B9CC"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>AndrewR</b> <br /><small>Member # 44</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,17,3,43,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 17, 2000</span> <span class="timeformat-0">03:43 AM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> Hi! I was just reading an article on sci.space.news about slowing down light - I just wanted to know -<P>Black holes have such an intense gravitational field that they slow down light or even suck it in... how!?! wasn't one of the properties of light - that it is pure energy - with no mass!?! If there is no mass how can the blackhole affect the light? if the light has no mass?<P>Thanks<P>Andrew<P>------------------<BR>"Who wouldn't be the one you love <BR> Who wouldn't stand inside your love." - <I>Stand Inside Your Love</I>, The Smashing Pumpkins <br /> </font> </td></tr> <tr bgcolor="#E5EAEF"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>Sol System</b> <br /><small>Member # 30</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,17,4,15,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 17, 2000</span> <span class="timeformat-0">04:15 AM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> Well, you're addressing two seperate issues here. First of all, light can be slowed down by changing the medium it travels through. This can easily be experimentally verified by sticking something into a pool. The object will appear bent because light is traveling slower in the water than it is in the air.<P>The rule about the speed of light applies more specifically to the speed of light in a vaccum. This is the speed beyond which one may not pass. (Actually, that isn't really true, theoretically. There is nothing in physics to prevent you from traveling faster than the speed of light. That's why tachyons are interesting speculation rather than crackpot theorizing. The problem is that nothing can travel at the speed of light, so you're left with no way to get to speeds beyond it.)<P>At any rate, energy and mass, according to Einstein, are interchangable. E=mc^2 and all that. Meaning that energy, like mass, is influenced by gravity. Why? Well, take the old example of space being a big rubber sheet, onto which are placed various objects like stars and black holes. These objects deform space (and time), creating the phenomenon we call gravity. Now, something to remember out light, again according to Einstein, is that it will always travel the shortest distance between two points. In other words, light travels in a straight line. Or does it? In a curved universe, the shortest distance is no longer a straight line. So light, when traveling near one of these large depressions in the fabric of space, follows the path of the shortest distance. And so it curves around objects of sufficient mass.<P>This property of light, and with it much of Einstein's theory, was confirmed by observing the sun during a total eclipse. Stars which we knew should have been behind the sun at the time showed up along the edges, because their light had been bent around the sun to hit our eyes and telescopes.<P>------------------<BR>"What did it mean to fly? A tremor in your soul. To resist the dull insistance of gravity."<BR>--<BR>Camper Van Beethoven<BR> <br /> </font> </td></tr> <tr bgcolor="#A3B9CC"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>Montgomery</b> <br /><small>Member # 23</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,17,5,53,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 17, 2000</span> <span class="timeformat-0">05:53 AM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> What he said. <IMG SRC="http://flare.solareclipse.net/wink.gif"><P>(Who says that Physics degree was a waste of time?)<P>------------------<BR>"O-PEN <B>FIRE!!!</B>" <br /> </font> </td></tr> <tr bgcolor="#E5EAEF"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>AndrewR</b> <br /><small>Member # 44</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,17,6,4,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 17, 2000</span> <span class="timeformat-0">06:04 AM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> Thankyou - I remember that rubber sheet analogy from Carl Sagan's superb Cosmos...<P>So, is it that light is actually being affected by gravity directly like we are to the earth, thus having a mass, or is it that its just some sort of 'field line' that makes the light bend around an object?<P>so does light (which I thought were just packets of Energy) exist as Energy AND matter - or only matter when it comes into contact with a Gravity field? If so, can we exist as Energy and Matter - and if we weren't near a --- ok big leap here--- if we weren't affected by the gravity of the Earth, Sun, planets and stars - exist as energy and matter? i.e. how can light (if I've guessed correctly) exist as both E and matter?<P>so DOES 'something' have to have MASS to be affected by gravity?<P>------------------<BR>"Who wouldn't be the one you love <BR> Who wouldn't stand inside your love." - <I>Stand Inside Your Love</I>, The Smashing Pumpkins <br /> </font> </td></tr> <tr bgcolor="#A3B9CC"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>Baloo</b> <br /><small>Member # 5</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,17,9,59,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 17, 2000</span> <span class="timeformat-0">09:59 AM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> Enough of the pseudoscientific claptrap.<P>Light does not slow down as it passes near a black hole, nor does it's path bend. Well, not exactly, anyhow. The truth is stranger than that.<P>The presence of mass affects the curvature of space. The greater the mass, the greater the curvature. A black hole is not so much a massive object as it is an incredibly dense <I>concentration</I> of mass.<P>For normal objects, the amount of bending is very slight, but measurable. During Solar eclipses, some stars which should be hidden by the Sun/Moon combination are visible because the Sun's gravity bends the space around it very slightly. This "lens effect" has the effect of "bending" the light's path, although in this case, what is actually happening is that the space itself is bent and the light is actually following a straight path through it.<P>There is another property which accounts for the apparent slowing of light as it passes near a black hole. As space is warped by an intense gravity field, time <I>slows</I> (time dilation) relative to the less-severely bent space further away. To an outside observer, the light appears to bend and red-shift. For objects travelling very near a black hole, time will seem to slow, as observed by someone much farther away -- to the object near the black hole, it's the rest of the universe that will seem to slow. It's almost as if they were travelling at a high percentage of the speed of light.<P>There's a neat website about this very subject:<P> <A HREF="http://casa.colorado.edu/~ajsh/schw.shtml" TARGET=_blank>http://casa.colorado.edu/~ajsh/schw.shtml</A> <P>Go have a look. The universe we live in can be pretty strange.<P>--Baloo<P>------------------<BR>"Lassie, her ears pricked up!"<P>--Atoth the Tamarian [From "Star Trek: Door Repair Guy"]<BR><A HREF="http://www.geocities.com/cyrano_jones.geo/" TARGET=_blank>http://www.geocities.com/cyrano_jones.geo/</A> <P> <br /> </font> </td></tr> <tr bgcolor="#E5EAEF"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>Sol System</b> <br /><small>Member # 30</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,17,13,25,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 17, 2000</span> <span class="timeformat-0">01:25 PM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> Um, that's pretty much exactly what I said. Though whether you call a black hole an infinitely dense object or a localized point of infinitely curved spacetime just depends on your point of view. They mean the same thing.<P>------------------<BR>"What did it mean to fly? A tremor in your soul. To resist the dull insistance of gravity."<BR>--<BR>Camper Van Beethoven<BR> <br /> </font> </td></tr> <tr bgcolor="#A3B9CC"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>Hobbes</b> <br /><small>Member # 138</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,17,20,0,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 17, 2000</span> <span class="timeformat-0">08:00 PM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> I'll have to keep close attention to this, I'm writing an eight page research paper on black holes.<P>Ever see the Stargate SG-1 episode about the black hole?<P>------------------<BR><I>"Tigers are mean! Tigers are fierce! Tigers have teeth and claws that pierce!"</I><BR><A HREF="http://members.tripod.com/thefsd" TARGET=_blank>Federation Starship Datalink</A> - On that annoying Tripod server, sucks don't it? <br /> </font> </td></tr> <tr bgcolor="#E5EAEF"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>TSN</b> <br /><small>Member # 31</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,17,21,27,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 17, 2000</span> <span class="timeformat-0">09:27 PM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> Andrew: I think the reason you're asking about this is that you assumed that gravity only affects matter. If you're Isaac Newton, this might be okay. However, as these others here have tried to explain, gravitt is not simply two pieces of matter pulling at each other. Gravity happens because things bend spacetime. If you have something really massive, it bends spacetime even more. When light is chugging along through space and it comes close to a star or a planet or a black hole, it hits this piece of bent spacetime and it bends its path to match. The star/planet/black hole doesn't reach out and "grab" passing objects. If this were the case, gravity would only affect matter. Instead, the star/planet/black hole curves spaetime, meaning that gravity affects <i>everything</i>, matter and energy alike.<P>------------------<BR>"To make the merry-go-round go faster, so that everyone needs to hang on tighter, just to keep from being thrown to the wolves."<BR>-They Might Be Giants, "They Might Be Giants" <br /> </font> </td></tr> <tr bgcolor="#A3B9CC"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>AndrewR</b> <br /><small>Member # 44</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,18,3,28,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 18, 2000</span> <span class="timeformat-0">03:28 AM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> Aha! Thankyou Baloo, Thankyou TSN - oh How I so wanted to be Sir I <IMG SRC="http://flare.solareclipse.net/wink.gif"> heh heh, yes I kept applying the 'grabbing' idea to light - light is ACTUALLY travelling in spacetime along its same path - its just that the path has warped/moved.<P>So is gravity a force or an effect? does the 'warping' idea happen say if you put two oranges infront of each other - put on an infintessimal scale?<P>------------------<BR>"Who wouldn't be the one you love <BR> Who wouldn't stand inside your love." - <I>Stand Inside Your Love</I>, The Smashing Pumpkins <br /> </font> </td></tr> <tr bgcolor="#E5EAEF"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>Sol System</b> <br /><small>Member # 30</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,18,23,54,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 18, 2000</span> <span class="timeformat-0">11:54 PM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> All mass creates gravity, whether its a planet or a pea. Furthermore, the effects of gravity are infinite in scope, meaning the gravity of that pea extends across the universe. However, not at levels that you could detect.<P>As to whether gravity is a force or not...it depends upon your point of view, really. Gravity can be explained as curvature, or in terms of a gravitational field. It's similar, though perhaps subtler, than the way light can be explained as both a wave and a particle. (Though in the case of gravity, its effects are the same regardless of your explanation of what it actual "is".)<P>I suppose, in theory, one could eventually find a way to explain the universe in such a way as to show that all the forces we see are really just effects of something else. In fact, I <i>think</i> that just such an explanation is part of string theory, but I wouldn't want to bet anything important on my sureness. <IMG SRC="http://flare.solareclipse.net/smile.gif"><P>------------------<BR>"What did it mean to fly? A tremor in your soul. To resist the dull insistance of gravity."<BR>--<BR>Camper Van Beethoven<BR> <br /> </font> </td></tr> <tr bgcolor="#A3B9CC"> <td valign="top" width="18%"> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <b>Omega</b> <br /><small>Member # 91</small> </font></td> <td width="82%"> <font size="2" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> <img src="https://flare.solareclipse.net/posticon.gif" border="0" alt=" - " /> posted <script language="JavaScript1.3" type="text/javascript"> document.write(timestamp(new Date(2000,2,19,1,7,0), dfrm, tfrm, 0, 0, 0, 0)); </script><noscript><span class="dateformat-0">March 19, 2000</span> <span class="timeformat-0">01:07 AM</span></noscript><hr /> </font> <font size="3" face="Trebuchet MS, Verdana, Helvetica, sans-serif"> Here's a question: does light itself have a gravitational pull?<P>Another, somewhat related: Hawking radiation, as I understand it. Supposedly, a particle with positive mass and a particle with equal negative mass can appear for a split second before annhilating each other with no release of energy (since negative mass means negative energy). Hawking radiation is where the negative particle gets seperated from the positive particle by the gravitational attraction of a nearby black hole. The negative particle falls into the black hole, canceling some of its mass/energy, and the positive particle escapes. But tell me: would a gravitational pull have any affect on negative matter? You'd think it'd just push it farther away.<P>------------------<BR>You are wise, witty, and wonderful, but you spend far too much time reading this sort of trash.<BR> <br /> </font> </td></tr> </table></td></tr></table> <br /> <br />
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