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 Black Holes, Light speed, and Time Travel Goto page 1, 2  Next
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Jedo the Jedi
Paragon in Training

 Posted: Thu Sep 23, 2004 12:40 am    Post subject: 1 Today in Physics class, we had a discussion about light speed and time travel. It came up that objects moving at a faster rate age slower than objects moving at a slower rate. For examle, a person running is aging slower than a person standing still. Of course, in this case, it's on a very small scale. The same is true of a person riding in an airplane and a person on the ground. Apparently, all of this is true because that, if you have a watch on, it enters into whatever "time zone" you are traveling in and the time therefore slows. Something like that. Thus, the person traveling at 600 mph in the airplane is moving slower through time than the person on the ground going 0 mph. Get it? All this talk of slower time at higher rates of velocity led to the subject of space travel and light speed. When someone goes up in a rocket, time slows and they age less quickly. The same is true of when you approach light speed. Hence, if a person were to travel at light speed, they would age slower because of their incredible rate of speed. We then stumbled upon the subject of distances shrinking when at light speed because light speed becomes the constant. This is where some questions came up. If the distances are "shrinking" you get there faster, right? Also, if you traveled at light speed for say one hour (from your perspective) and you came back to earth, it would almost be as if you had traveled into the future, right? So, theoretically, time travel is possible, into the future anyway. But what if you taveled backwards at light speed? If you were to go backwards at light speed, then, theoretically, you would be catching the light particles coming off of somebody doing something, and eventually you would catch up to light particles coming off somebody that did something in the past. Wouldn't that be traveling into the past? Just some thoughts I had, and questions I wanted answered. I have some questions about the nature of Black Holes and dark matter too, but I figured that this was enough for now.
mudbuck
Dirty Dollar

 Posted: Thu Sep 23, 2004 1:28 am    Post subject: 2 You can't actually travel backwards in space, nor forwards. There is no specific directions in space, just locations from one point to another. The reason why time goes slower for objects in motion exponentially is because existance.exe has a lot of lag time when dealing with ridiculous speeds. The speed of light is actually the program designer's way to prevent the program from crashing. Oh, and if you do try this someday, don't. A single particle would penetrate a hole the size of your house at those speeds. If anyone ever sees the computer that runs existance.exe, please don't push Crtl+Alt+Delete_________________1000oclock.com
+1

 Posted: Thu Sep 23, 2004 1:36 am    Post subject: 3 Time dilation has nothing to do with your watch. You could be a naked pigmy or even just a muon traveling at .99C and time would still appear to move slower for you than for the outside world. I'll leave the explanation to someone more versed than me. Also, you can't travel at a negative velocity. And you can't ever catch light. No matter how fast you go (unless it's the speed of light) it will always be moving away from you at the speed of light._________________And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.
Courk
Daedalian Member

 Posted: Thu Sep 23, 2004 1:42 am    Post subject: 4 You can travel at a negative velocity. You just can't travel at a negative speed.
+1

 Posted: Thu Sep 23, 2004 1:54 am    Post subject: 5 Meh. I'll just stay out of this._________________And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.
extro...
Guest

Posted: Thu Sep 23, 2004 2:10 am    Post subject: 6

 Jedo the Jedi wrote: But what if you taveled backwards at light speed? If you were to go backwards at light speed, then, theoretically, you would be catching the light particles coming off of somebody doing something, and eventually you would catch up to light particles coming off somebody that did something in the past. Wouldn't that be traveling into the past?

As Samadhi points out, you'd have to travel faster than light to catch up with light particles "from the past" (i.e. ones that were here, where you started, in the past). And then even if you did, you'd only be able to turn around, and with a really spiffy telescope, look back and see the past. But you wouldn't be able to visit it in a way that would let you affect it. As far as seeing the past, that's hardly any big deal. Just read yesterdays paper. Well, that's only a record of yesterday, but then that's all those light particles would be if you could catch up with them.

The rules seem to be: You can see the past, and you can affect the future. You can't affect the past, or see the future. As for the present, it's too fleeting to deserve consideration.
Phil_The_Rodent
Daedalian Member

 Posted: Thu Sep 23, 2004 2:47 am    Post subject: 7 You can see into the past anytime you like. look up
Jedo
Guest

Posted: Thu Sep 23, 2004 3:07 am    Post subject: 8

 Quote: Time dilation has nothing to do with your watch. You could be a naked pigmy or even just a muon traveling at .99C and time would still appear to move slower for you than for the outside world. I'll leave the explanation to someone more versed than me.

Yeah, I understand that. I was just using the watch thing as an example because it's really the only way that you can see the effects, right? Or would it still appear to be ticking away at the same speed?

 Quote: As Samadhi points out, you'd have to travel faster than light to catch up with light particles "from the past" (i.e. ones that were here, where you started, in the past)

I seem to remember now that this was how it was explained. I was just so confused then that I completely forgot about having to go faster than the speed of light. And, mudbuck, what were you talking about?
mathgrant
A very tilted cell member

 Posted: Thu Sep 23, 2004 5:10 am    Post subject: 9 I don't believe in time dilation. It's too complicated._________________My logic puzzle blog
Chuck
Daedalian Member

 Posted: Thu Sep 23, 2004 5:23 am    Post subject: 10 There are no black holes. They're a mathematical placeholder until we figure out what's really going on.
Celt
still thinking

Posted: Thu Sep 23, 2004 3:15 pm    Post subject: 11

 Jedo the Jedi wrote: Also, if you traveled at light speed for say one hour (from your perspective)
I'm no expert, but as someone interested in this kind of stuff, here's how I perceive it.

When you travel at light speed, time stands still for you so that from your perspective you get where you want to go instantaneously. There is no travelling at light speed for an hour from your perspective.

Imagine you start at speed 0 and begin accelerating quickly towards your destination, a planet very far away. As you get closer to the planet, space will seem to contract so that the planet appears closer and becomes narrower and more disc-like as you approach the speed of light. It would seem to you that the universe is being squashed from 3 dimensions to 2 dimensions so that by the time you reached light speed, everywhere in front of you would appear to be 2-dimensional to you and you would in fact be everywhere along the path to your destination at the same time. To an observer on the planet, it would appear as though your space ship had stretched itself until it collided with your planet and obliterated a large chunk of it along with your ship.

Travelling at the speed of light is very dangerous, as you never know "when" to stop.
+1

Posted: Thu Sep 23, 2004 5:23 pm    Post subject: 12

 Quote: Yeah, I understand that. I was just using the watch thing as an example because it's really the only way that you can see the effects, right? Or would it still appear to be ticking away at the same speed?
YOUR watch would still tick away at the same speed, because it's in your frame of reference. If you were able to observe a watch in another frame of reference, it would appear to be going faster (or slower if that frame of reference is closer to C) than your watch.

 Quote: When you travel at light speed, time stands still for you so that from your perspective you get where you want to go instantaneously.
Well, there's a little bit of difficulty with that. As you approach C, your mass increases asymptotically towards infinity. If you were travelling the speed of light, your mass would be infinite and the energy needed to accelerate you there would be infinite.

I was going to post a formula image but GLPICS hates me right now, and I can never seem to get my own ftp to work at work. Bah.

m = m 0 /sqrt(1-v 2 /c 2 )
_________________
And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.
Aarondalf
the original GL stud

 Posted: Fri Sep 24, 2004 9:10 am    Post subject: 13 Lol, anyone else think Jedo's initial post has all the workings of a spectacularly crappy science fiction novel? Samadhi, you think its hard to UPLOAD the formula? Try deriving that shit.
+1

 Posted: Fri Sep 24, 2004 5:38 pm    Post subject: 14 Oh hell no. I read Einstein's "Relativity: The Special and the General Theory." The note below the title was "A simple explanation that anyone can understand" or something like that. Riiiiiiiiight. I got it, but I had to keep rereading and going back. It's a tough notion to get your mind around._________________And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.
Aarondalf
the original GL stud

 Posted: Sat Sep 25, 2004 12:19 am    Post subject: 15 The real pain is that once you actually know the equations, to actually get anything practical out of it you have to know a heap of complex physics that doesnt even relate to relativity.
Jedo the Jedi
Paragon in Training

Posted: Sat Sep 25, 2004 3:24 pm    Post subject: 16

 Quote: Lol, anyone else think Jedo's initial post has all the workings of a spectacularly crappy science fiction novel?

Well, Aarondalf, you're half right there. Not about the actual post or anything, but I would like to right a science fiction novel some day. It wouldn't be crappy, though, because then it would tarnish the name of Star Wars, which is the type of book I'd like to write. Unfortunately, I don't think I'm a good enough writer for that, but I can always dream.

So, why is light speed so dangerous? Just because we don't know enough of the known universe to plot safe courses and when to stop? I mean, in Star Wars they know all that stuff, we could too. I do realize that Star Wars is fiction, but it's not altogether impossible. Of course, we'd have to build the equivalent of a hyperdrive first.

Also, Chuck, what do you mean black holes don't exist? I was under the impression that they did. If they're just a place filler, are they filling the place of dark matter which supposedly comprises 90% of the universe and is ever expanding? (so I heard) What's the deal here?
Chuck
Daedalian Member

 Posted: Sat Sep 25, 2004 3:51 pm    Post subject: 17 We don't know what happens when matter is concentrated to extremely high densities. All we have are theories based on the physical laws that we've observed locally. We don't even know if we have all the forces of nature accounted for yet. There appear to be some very dense objects out there but that doesn't mean that light can't escape from them or that they have infinitely dense singularities at their cores. Anyway, since time slows in gravitational fields it would take an infinite amount of time for a black hole to form. Even if they are possible, there aren't any yet.
Leptonn
Guest

 Posted: Fri Oct 01, 2004 3:37 pm    Post subject: 18 Aarondalf, And if you think Special Relativity is hard, take a stab at General Relativity... I have found that you can see (algebraically) most of the well-known SR experiments that have been done (flying atomic clocks in 747s, decay time of a high-velocity particle, etc). Jedo, The derivation is a bit finicky, but it isn't hard to show that the energy required to boost a particle from zero velocity to the velocity of light exactly will require an infinite amount of energy. The SR spacetime metric is symmetric, though, so a particle (or spaceship) that somehow started out travelling faster than the velocity of light would require an infinite amount of energy to slow down to the velocity of light. Don't get your hopes up, though - searches for these so-called tachyons have thus far come up empty. The first experimental evidence (in a law court, it would be circumstantial) for black holes has just come in during the last few years. Astronomers have detected white dwarf stars that are orbiting around something with a mass larger than the Chandrasekhar Mass, in other words, something that should have collapsed in on itself to become a black hole, if our theory is right. Other astronomers believe that supermassive black holes lie in the center of some galaxies. These black holes are believed to be the source of extremely high-energy radiation that might be emitted by matter spiralling into the hole. Borodog's PhD was on a similar phenomenon involving neutron stars, which are collapsed stars that are slightly below the Chandrasekhar limit. However, Chuck is right. There is no viable physical theory to explain what happens at the center of a black hole. Einstein's General Relativity gives what we have come to call a singularity - a point with something like infinite mass - if the black hole doesn't rotate. A rotating black hole may give rise to a ring-shaped singularity. Some people hope that Superstring Theory (aka M-Theory) will eventually tell us, since it combines the force of gravity, which seems to deal well with large masses, and quantum mechanics, which seems to deal well with tiny distances. Dark Matter is a highly-speculative theory to describe why galaxies rotate in the way that they do. If you look at a spiral galaxy, the apparent mass in it (including black holes) isn't enough to make it rotate the way it does. Astronomers thus suggest that most of the mass in the universe is dark - in other words, it doesn't interact with matter except through the force of gravity. Dark Energy is a ridiculously speculative theory that has only come up in the last few years. Observations of giant galaxies from a couple billion years after the universe's apparent formation (Big Bang?) show that the universe is expanding much faster than it used to be. The galaxies are far enough away that the light from them has been travelling most of the age of the universe. The expansion of the universe is like a loaf of bread rising - it's not really expanding *into* anything, it's just getting larger as seen from someone on the inside. Now, the speed at which these galaxies are moving away from us tells us the speed of the expansion of the universe, but by the same token, it's hard to tell exactly how fast the buggers are moving away. In any case, the point may be moot because the results that the dark energy theorem rests on are extremely uncertain. Hopefully this has been helpful.
One Skunk Todd
Smelly Member

 Posted: Fri Oct 01, 2004 4:13 pm    Post subject: 19 How can they tell that the rate of expansion has changed?
+1

 Posted: Fri Oct 01, 2004 6:38 pm    Post subject: 20 Super novas appear dimmer than they should. Leptonn: Is this dark energy you're talking about the same as the 'vacuum energy' as it were?_________________And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.
One Skunk Todd
Smelly Member

 Posted: Fri Oct 01, 2004 8:36 pm    Post subject: 21 Samadhi, is there a more detailed, yet still lay, explanation than that?
+1

 Posted: Fri Oct 01, 2004 8:59 pm    Post subject: 22 Probably._________________And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.
Lucky Wizard
Daedalian Member

 Posted: Sat Oct 02, 2004 12:12 am    Post subject: 23 I actually did a report on the accelerating universe theory once; though I don't have it on hand, I do remember a good portion of the theory, and looking things up online just now has helped me fill in some things I couldn't remember. There are two types of supernovas; there is the better-known kind where a supergiant star's life ends with an explosion, and another kind that occurs when a white dwarf star's gravitational attraction causes matter from another star close at hand to separate from the other star and build up onto the white dwarf until the white dwarf gets so massive that it collapses. The latter kind -- called Type Ia -- happens to have a predictable luminosity, and we can distinguish these two kinds by their spectrum. Hence, by examining the apparent brightness of these supernovae, we can compare how bright it appears with how bright it is, which tells us how much the light has diffused and therefore how far away it is. But of course, there are other ways to measure distance. We can determine the speed of the object; since space is expanding uniformly, the rate at which the objects run away from us tells us how far we are from the object in question, since if they're closer they'll move away at a slower speed; this is because the uniformness of the expansion indicates that the distance it moves is proportional to the distance it already is from us. This redshift measurement, of course, assumes that the rate of expansion has not changed; if in fact the rate of expansion was slower once, then it'll be moving slower than its distance would suggest, because the light left it a long time ago when the expansion rate was slower. So we have two ways to measure the distance of a type Ia supernova. A few years back several teams, including a Harvard team that announced the discovery, compared the two measurements and discovered something odd. Namely, the two distance measurements do not line up; the supernovas were moving slower when the light was given off than the distance (as measured by the supernova's brightness) would suggest if the rate of expansion had never changed. This, of course, suggests that the rate of expansion was slower once, but is now faster. Hope that helps.
Leptonn
Guest

 Posted: Sat Oct 02, 2004 10:18 pm    Post subject: 24 Samadhi, Dark energy is vacuum energy. There's still no real conception exactly what the stuff is, though... Some people think of it as Einstein's Cosmological Constant, Lambda: G nu,mu = 8 * pi * G * Lambda * T nu,mu (that's the Einstein gravity tensor equation, btw... G nu,mu is the force of gravity while T nu,mu is the geometry of space and time)
+1

 Posted: Sun Oct 03, 2004 12:35 am    Post subject: 25 Figured you were probably talking about the same thing, I just hadn't heard it referred to as that._________________And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.
Leptonn
Guest

 Posted: Mon Oct 04, 2004 10:11 pm    Post subject: 26 (Colloquialism of catchphrase) = constant * (amount of funding received)
tinman
Guest

 Posted: Tue Dec 14, 2004 6:57 am    Post subject: 27 Experiments here on Earth have already proved you can travel faster than light. You have to relize we do not no everything yet. If you look into Quantem Mechanix youll get an idea of another view of science. Light travels all kind different speeds depending where you are in Glax.....comunication and travel is by rope pull tecnology. Experiment take a pencil slowly pull it across table. It went faster than light. Proff: If a Lazer beam was same lenghth as pencil and you pulled it and pencil at same time and speed the pencil would move faster.....because the tip of Lazer bean would have a lag time before moving of 186000 mps. Hence rope pull tecnoligy beat out light. Its done using Aeighter in real space travel. tinman
tinman
Guest

 Posted: Tue Dec 14, 2004 7:12 am    Post subject: 28 Just keep in mind people on Earth at this time are only equiped with Victorean Science and most have not seen Hyper Demensional effects in play. We had two huricanes that opned up 5 th demension and had hyper caracter eyes this year, Prof: Remember hurican that stalled of your Florida....for 42 min, then went from level 3 to level 4........I went to weather got photos of the Hyper Mate in eye by working backward I got to photos of weather channel of hyper eyes with the Quantem Mec 3 d effects at work. Have same now. Its so subtle to normal person they did not no what it was. Just keep open mind to facts that you are not fully aware of the sciences that are avalible yet. There are multiple demensions....to avoid G force the whole ship is transformed encluding pilot into Photon state.......so 90 degree flight caracterists are possible. Another speeds are 100"s thousands times faster than light. For ships....in Galaxy. Why Hyper weather now...we are passing through a flux field in the Galaxy youll see some real different things, as those huricane eyes. Just wanted to check in thanks for the time keep mind open with it you can go anywhere just have to no how......tinman
Travis
Daedalian Member*

 Posted: Tue Dec 14, 2004 7:25 am    Post subject: 29 Finally, someone who knows what they're talking about. Thanks, tinman.
...zere's a fly een my zoop!

 Posted: Tue Dec 14, 2004 2:21 pm    Post subject: 30 Interesting views tinman. Granted I am just a curious person when it omes to "real" science, I don't pretend to know even a little of the stuff that i should. i remeber the basic stuff that i learned from grammar through high scholl and that is it. I just find it interesting._________________Duct tape is like the force they both have a light side and a dark side and they bind the universe together.
MTGAP
Daedalian Member

Posted: Tue Aug 12, 2008 3:12 am    Post subject: 31

 mudbuck wrote: Oh, and if you do try this someday, don't. A single particle would penetrate a hole the size of your house at those speeds.

No it wouldn't. A molecule moving at near the speed of light would have no effect whatsoever on a person. Molecules are very small.
_________________
This statement is false.
MTGAP
Daedalian Member

Posted: Tue Aug 12, 2008 3:27 am    Post subject: 32

 Samadhi wrote: Also, you can't travel at a negative velocity. And you can't ever catch light. No matter how fast you go (unless it's the speed of light) it will always be moving away from you at the speed of light.

That's exactly why time changes. Actually, if you are moving the speed of light, light appears to be moving away from you at the speed of light. But to an outside observer, it looks like you're both moving at the same speed. For that to work, time has to be stopped, so to you it looks like you're not moving. That's why moving at the speed of light causes time to stop; it assumes that the speed of light is constant at any inertial reference frame.

 Quote: xperiments here on Earth have already proved you can travel faster than light. You have to relize we do not no everything yet. If you look into Quantem Mechanix youll get an idea of another view of science. Light travels all kind different speeds depending where you are in Glax.....comunication and travel is by rope pull tecnology. Experiment take a pencil slowly pull it across table. It went faster than light. Proff: If a Lazer beam was same lenghth as pencil and you pulled it and pencil at same time and speed the pencil would move faster.....because the tip of Lazer bean would have a lag time before moving of 186000 mps. Hence rope pull tecnoligy beat out light. Its done using Aeighter in real space travel.

That is not true. My proof: your spelling sucks.

Can anyone explain the twin paradox?
_________________
This statement is false.
Zag
Tired of his old title

 Posted: Tue Aug 12, 2008 2:35 pm    Post subject: 33 I've always had a question about this whole "Time is slower for the guy moving" issue. Is it really about acceleration? Because, after all, motion is relative. If I fly out at about a light year away from Earth, then turn back and accelerate towards Earth so that my velocity is 0.9 c and shut off my engines, then I'm an inertial reference frame just as good as Earth is. In other words, from my point of view, I'm stationary and Earth is moving by me at 0.9 c. So do I see all the clocks on Earth as running slower than mine?
MTGAP
Daedalian Member

Posted: Tue Aug 12, 2008 4:46 pm    Post subject: 34

 Zag wrote: I've always had a question about this whole "Time is slower for the guy moving" issue. Is it really about acceleration? Because, after all, motion is relative. If I fly out at about a light year away from Earth, then turn back and accelerate towards Earth so that my velocity is 0.9 c and shut off my engines, then I'm an inertial reference frame just as good as Earth is. In other words, from my point of view, I'm stationary and Earth is moving by me at 0.9 c. So do I see all the clocks on Earth as running slower than mine?

You are correct. That's the twin paradox. There is some reason why it makes sense for everyone to see everyone else as moving slower.
_________________
This statement is false.
Lepton
1:41+ Arse Scratcher

Posted: Fri Aug 15, 2008 9:22 pm    Post subject: 35

Yep, Zag, if you accept that time dilation exists, then both people will see it. The "twin paradox" goes something like this:
 Quote: There are twins, Alice and Bob. Alice takes her rocket ship for a ride at 0.9c for a while, then returns to Earth. Are Alice and Bob still the same age?

The true answer -- that Alice will be younger than Bob -- is the paradox. From Bob's point of view, Alice's internal clock will have been ticking slower, so Bob would expect Alice to be younger. The paradox is resolved by noting that, since Alice has to accelerate (taking off, turning around, landing), Alice's calculations are not simple like Bob's.
MTGAP
Daedalian Member

Posted: Sat Aug 16, 2008 4:57 pm    Post subject: 36

Lepton wrote:
Yep, Zag, if you accept that time dilation exists, then both people will see it. The "twin paradox" goes something like this:
 Quote: There are twins, Alice and Bob. Alice takes her rocket ship for a ride at 0.9c for a while, then returns to Earth. Are Alice and Bob still the same age?

The true answer -- that Alice will be younger than Bob -- is the paradox. From Bob's point of view, Alice's internal clock will have been ticking slower, so Bob would expect Alice to be younger. The paradox is resolved by noting that, since Alice has to accelerate (taking off, turning around, landing), Alice's calculations are not simple like Bob's.

Right, the person who accelerates is the one who changes. But there's still something weird about that. To her, it looks like Bob is younger. But at some point, Bob suddenly becomes older. What point is that?

Another similar question is this. Suppose Alice travels at the speed of light. There is a photon in front of her. Bob sees that Alice and the photon are moving at the same speed, and aren't moving relative to each other. Alice sees that the photon is moving away from her at the speed of light, and everything else is moving behind her at the speed of light. But for the photon to move at all from her perspective, she has to go infinitely far. But to her it looks like she's only going at the speed of light for an arbitrary finite amount of time. So at what point does she see it as being infinitely far?

Those are really the same question, but I thought of them both independently before I realized they were the same.
_________________
This statement is false.
Lepton*
Guest

Posted: Sat Aug 16, 2008 7:31 pm    Post subject: 37

 MTGAP wrote: Right, the person who accelerates is the one who changes. But there's still something weird about that. To her, it looks like Bob is younger. But at some point, Bob suddenly becomes older. What point is that?

When she is accelerating (all three times). In fact, Bob will never look "younger" to Alice; when Alice is cruising, she'll think that he is aging more slowly.

 Quote: Another similar question is this. Suppose Alice travels at the speed of light. There is a photon in front of her. Bob sees that Alice and the photon are moving at the same speed, and aren't moving relative to each other. Alice sees that the photon is moving away from her at the speed of light, and everything else is moving behind her at the speed of light. But for the photon to move at all from her perspective, she has to go infinitely far. But to her it looks like she's only going at the speed of light for an arbitrary finite amount of time. So at what point does she see it as being infinitely far?

Alice *cannot* travel at the speed of light, because it would take an asymptotic infinity of energy to accelerate to that point. If Alice is massless, then she can (in fact, must!) travel at the speed of light... but then, her internal clock has stopped (time dilation is infinite) so that concepts like speed are meaningless.
MNOWAX
0.999... of a Troll

 Posted: Sat Aug 16, 2008 8:45 pm    Post subject: 38 *head starts to swell and blows into a million pieces*_________________The Man The Myth The Legend MNOWAX
MTGAP
Daedalian Member

Posted: Sun Aug 17, 2008 4:12 am    Post subject: 39

Lepton* wrote:
 MTGAP wrote: Right, the person who accelerates is the one who changes. But there's still something weird about that. To her, it looks like Bob is younger. But at some point, Bob suddenly becomes older. What point is that?

When she is accelerating (all three times). In fact, Bob will never look "younger" to Alice; when Alice is cruising, she'll think that he is aging more slowly.

That's what I meant. Bob looks younger relative to Alice.
 Quote: Alice *cannot* travel at the speed of light, because it would take an asymptotic infinity of energy to accelerate to that point. If Alice is massless, then she can (in fact, must!) travel at the speed of light... but then, her internal clock has stopped (time dilation is infinite) so that concepts like speed are meaningless.

Just because they're meaningless doesn't mean there's no reason to ponder an answer. Just because there's no reason to ponder an answer doesn't mean we shouldn't ponder an answer. Pondering an answer is fun.[/quote]
_________________
This statement is false.
Amb
Amb the Hitched.

 Posted: Fri Sep 12, 2008 11:00 am    Post subject: 40 Isn't it useful to know some scientists now believe the speed of light itself can accelerate and slow down....
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