Time travel (209)

1 Name: Anonymous Scientist : 2006-07-20 11:12 ID:6bO6LaVD

Do you think it's possible?

60 Name: Anonymous Scientist : 2006-11-21 09:18 ID:Heaven

and i mean 'faster than the speed of light'.. not light itself -__-;

61 Name: Anonymous Scientist : 2006-11-21 13:26 ID:Heaven

>How is it possible for me to look at women yet not be able to become one?

Becoming something is not the same as traveling to something.

62 Name: Anonymous Scientist : 2006-11-21 23:51 ID:JXZ4g7yq

> Why can you travel @ the speed of light (light does this) but not actually go 1m/s faster than it?

Because "1m/s faster than light" is a meaningless concept. You only think it makes sense because you are used to very low velocities. Your intuitive image of the universe is nowhere near correct, and it is that incorrect image which makes you think moving faster than light makes sense.

It has nothing to do with light itself. Light just happens to move at the maximum possible speed. The structure of the universe is such that moving faster than light is not something that can happen.

63 Name: Anonymous Scientist : 2006-11-21 23:53 ID:JXZ4g7yq

> Becoming something is not the same as traveling to something.

Similarly, seeing something is not the same as travelling to it.

64 Name: Anonymous Scientist : 2006-11-22 09:20 ID:Heaven

>the maximum possible speed. The structure of the universe is such that moving faster than light is not something that can happen.

yeah, and there cant be life without water... lolz

65 Name: Anonymous Scientist : 2006-11-22 13:03 ID:E4evLiqi

>>64

I am telling you the truth, but you refuse to listen, so what can I do? Well, I guess I can tell you what happens if you try to go faster than light. Please try and read and understand at least some of this.

Let's say you build a rocket with a REALLY big and powerful, yet extremely light-weight, engine. This is currently impossible, but that might just be engineering so we can easily disregard it, as you like to do.

In the first case, let's just set off the rocket and watch it go. You'll see it accelerate up towards the speed of light, just as you expect. However, when it starts to get close, you notice it's not accelerating as much as it should any longer. This is pretty confusing, since the engine is still putting out just as much thrust. Investigating closer (with your strange futuristic equipment), you notice that although the engine is still running correctly, the rocket is suddenly heavier. You will also notice that the close to the speed of light you get, the heavier the rocket will become, and the less it will accelerate.

When the rocket gets really close to the speed of light, its mass has grown enormous. The engine still tries to accelerate it, but it's not doing much good any longer. It will never reach the speed of light, but if it did, its mass would be infinite, and the engine could no longer move the rocket.

Incidentially, you will also find that the rocket has become shorter, and that clocks on board it are running slow. If the rocket should ever reach the speed of light, it would be completely flat, and time would stand still on board it.

Now, in the second test, let's jump aboard that rocket and try to ride it up to the speed of light. At first, everything goes well. The rocket accelerates just as it should. From our previous experiment, we might expect that it will soon stop doing this, because of the mass increase. However, to our surprise, everything is working just fine. But when we look out of the window, we suddenly notice that the entire universe around is shrinking along the direction of travel. Even though we keep accelerating, we never seem to get past the speed of light relative to anything outside the rocket - we reach places that used to be far away quickly, but it is not because we ourselves are moving fast, it's because the rest of the universe is shrinking!

We will reach Alpha Centauri in, say, three hours. But we know from our previous experiment that that rocket reached Alpha Centauri in three hours too, by its internal clock, which was running slow!. Sitting outside the rocket and waiting for it to reach Alpha Centauri took the expected four years, but the internal clock had slowed down so much, it only ever counted up three hours.

None of this is fanciful theory - this is all confirmed every single day, by particle accelerators and GPS satellites. This is how the universe works. It seems very strange, and it seems totally wrong compared to our experience, but it is actually our experience that is incorrect.

66 Name: Anonymous Scientist : 2006-11-27 04:05 ID:vgIuB127

ok suppose that we have a looooooooooong tube with inside diameter of 1 cm and length of 10 light seconds. and in side this tube is full of small 0.9 cm metallic spheres lined up from one end to the other. so you push the first sphere. with common sense, you might think that on the other end of our tube, a sphere drops instantaneously right? I mean, nothing is moving faster that the speed of light right? you are just pushing one sphere slowly and on the other end, no matter how long the tube is, one should come out of the tube.
sorry pal, but that’s not the case, its going to take 10 seconds. Practical observation: electricity , more or less is the same concept and it doesn’t travel faster than light. if can’t defy space. how are you going to defy time? the two are closely connect as far as I have heard. so nope: no time travel unless you break space and the laws of universe in some manner.

67 Name: Anonymous Scientist : 2006-11-27 09:32 ID:mXCNc57F

scientists are known to have slowed the speed of light down, and there was an incident in a russian nuclear reactor, i cant remember what it was, but there was some matter that travelet faster than the speed of light.

google for it, it's there..

68 Name: Anonymous Scientist : 2006-11-27 17:28 ID:JXZ4g7yq

>>67

Light travels at less than "the speed of light" in a medium. When people say "the speed of light", they actually mean "the speed of light in a vacuum", also known as c. Travelling faster than the speed of light in a medium is not only possible, it happens all the time around nuclear reactors. It causes a phenomenom known as Cherenkov radiation, which incidentially is quite pretty: http://images.vertmarkets.com/crlive/files/Images/8B3B7B58-B579-11D4-8C77-009027DE0829/jgglow.jpg

This is why the "light" part of "the speed of light" is not important. Light doesn't always travel at the "speed of light". The constant c exists independently of the fact that light travels at that speed in a vaccuum. Other things travel at that speed too - gravity being one of them.

69 Name: Anonymous Scientist : 2006-11-29 12:12 ID:Heaven

im not talking about light itself.. just the speed it has.

70 Name: Anonymous Scientist : 2006-12-09 02:09 ID:vnkaDxrv

Didn't Kurt Godel have something important to say about time travel in relative space.

71 Name: Anonymous Scientist : 2006-12-10 18:10 ID:Heaven

Gödel was a mathematician, not a physicist.

72 Name: Anonymous Scientist : 2007-01-30 21:51 ID:QPZM8lgA

From Wikipedia's article on "Kurt Godel."

"In the late 1940s, Gödel demonstrated the existence of paradoxical solutions to Albert Einstein's field equations in general relativity. These 'rotating universes' would allow time travel and caused Einstein to have doubts about his own theory."

More detailed information about this body of work can be found here:

http://infoshare1.princeton.edu/libraries/firestone/rbsc/finding_aids/mathoral/pmcxgod0.htm

Also, 72GET!!!

73 Name: Anonymous Scientist : 2007-01-31 12:31 ID:Heaven

>>72

Well, you learn something new every day!

74 Name: Anonymous Scientist : 2007-02-01 22:59 ID:OodQrro+

>>66

almost. it does happen pretty much simultaneously with the first ball. it will simply take 10 seconds to observe the ball fall out of place, because of the distance the light has to travel to reach back to you. an observer at the other end will see the ball fall out of the tube before you push it, in theory. thats also assuming you can even move that many small metal bearings. they should weigh in the vicinity of several tonnes.

75 Name: Anonymous Scientist : 2007-02-02 01:45 ID:JXZ4g7yq

>>74

That's plain and simply wrong. It will take at least 10 seconds, in practice much, much longer, before the last ball starts to move. The reason it takes longer is that the pressure will move through the system at the speed of sound, not the speed of light. The speed of sound in a metal is pretty high, but it's much less than the speed of light.

76 Name: Anonymous Scientist : 2007-02-02 08:23 ID:pCdOblrF

>>75
so the energy you apply to item #1 moves to item #2 and so on. but, assuming we has something strong enough to push them all, wouldnt that mean that either 1) the metallic bearings would change shape, or even break under the pressure or 2) two bearings will occupy the same space at the same time. assuming the bearings are indestructable, neither scenario seems likely. but im also imagining a constant application of pressure, not a impact, like you see on those desk-ornaments with the balls on string.

using that balls-on-string example, lets say you have one of those desk ornaments. if you pick up one ball, and let go, the last ball moves. i understand thats because of the energy wave moving, and i understand it happens at the speed of sound. but do you mean to tell me that if, for instance, you had those five balls at rest next to each other, and you pushed one, (not drawing it back and releasing, just pushing it foward) that the balls dont move as if they were one object? the same thing should happen in this tube. if one thing is pushing on these bearings, then all the bearings should move in unison, so long as the force is sufficient enough to move them all.

77 Name: Anonymous Scientist : 2007-02-04 15:35 ID:JXZ4g7yq

> wouldnt that mean that either 1) the metallic bearings would change shape, or even break under the pressure

Yes.

> assuming the bearings are indestructable

They are not, and no such material exists, or even can exist.

> but do you mean to tell me that if, for instance, you had those five balls at rest next to each other, and you pushed one, (not drawing it back and releasing, just pushing it foward) that the balls dont move as if they were one object?

Yes, I mean exactly that. It is not noticable under normal circumstances because the speed of sound in the material is so high in comparison to the speed you move them at, which is why your intuitive sense of the world does not accept it easily.

78 Name: Anonymous Scientist : 2007-06-24 22:55 ID:Zv2mBs0a

>>59 The only way to travel faster than the speed of light is by cheating. Usually this involves parallel dimensions or creating a "warp bubble" around you spaceship.
The reason you can't travel faster than light is, basically, because you can't.

79 Name: Anonymous Scientist : 2007-06-25 19:55 ID:X4CV/S9s

It's possible. Very likely too if you consider the following "time travel"

You could build spaceship that accelerates at 1g. It would take you 24 years to get to Andromeda galaxy in your time frame, remember you would be going at relativistic speeds (time dilation). But us here on earth, we would see you on your way for millions of years.

80 Name: Anonymous Scientist : 2007-07-21 07:09 ID:FeesWdyy

http://www.dailygalaxy.com/my_weblog/2007/07/weird-science-2.html

There. I guess it's not just normal people who believe this shit. The project funders must have too much money in their hands.

81 Name: Anonymous Scientist : 2007-07-30 14:53 ID:TxHhdkbQ

>>39 ya , lol

82 Name: Anonymous Scientist : 2007-07-31 04:42 ID:Qix6jNpG

If time travel to the past was possible, we'd currently be flooded by otakus from the future who want to catch original broadcasts of Lucky Star.

83 Name: Anonymous Scientist : 2007-07-31 12:21 ID:sW+pmhcT

>>82 The RIAA from the future will not allow it for copyright reasons.

84 Name: Anonymous Scientist : 2007-10-12 05:19 ID:T9RzPwMp

Believe Einstein. I think you can go into the future if you can travel at the speed of light. I think it's true that it is relative to the space you are in so as you travel at the speed of light it might not seem like you have aged but you return and everyone else will be older depending on how long you were away. Maybe it is not time travel but age travel.

85 Name: Anonymous Scientist : 2007-10-12 13:07 ID:sW+pmhcT

Semantics.

86 Name: Anonymous Scientist : 2007-10-12 16:20 ID:Heaven

I'm going into the future right now!

87 Name: Anonymous Scientist : 2007-10-13 00:13 ID:Heaven

reverse the polarity.

88 Name: Anonymous Scientist : 2007-10-13 12:10 ID:sW+pmhcT

Great Scott! Where are you going to find 1.21 gigawatts??

89 Name: Anonymous Scientist : 2007-10-13 15:03 ID:+Swof75c

all time is occurring simultaneously. It's like pictures in a flip-book. All other informationis classified.

90 Name: Anonymous Scientist : 2007-10-15 07:48 ID:J+ol/sfP

no its not possible, period.

91 Name: John Titor : 2007-10-15 23:40 ID:Heaven

It's real, and I can prove it!

I just don't feel like it...

92 Name: Anonymous Scientist : 2007-10-18 02:19 ID:kbhYcDY3

SEE I DID IT!!

93 Name: Anonymous Scientist : 2007-10-18 02:20 ID:kbhYcDY3

I can travel back in time to >>92

94 Name: Anonymous Scientist : 2007-10-19 07:22 ID:idwUBqtg

Nobody managed to go backward, and so far it seems impossible,...

95 Name: Anonymous Scientist : 2007-10-19 11:41 ID:Heaven

>>94

What, >>93 totally did it!

96 Name: Anonymous Scientist : 2007-10-19 13:24 ID:sW+pmhcT

I can go backward any time, the problem is how to bring my body with me.

97 Name: Marty McFly : 2007-10-21 21:49 ID:6cEGOR5r

I managed to do it at least to years ending in "5", and then I had to go and wreck the delorean... At least now I have something that travels between years ending in "7", so welcome summer of love!

98 Name: Anonymous Scientist : 2007-10-21 22:01 ID:6cEGOR5r

Stephen Hawking once tried to prove time travel was impossible by means of a convoluted argument that took into account several factors, and then tried to argue that all of them didn't work, probably in an effort to explain why he considered such things as the "grandfather paradox" to be impossible. Seems to run afoul of Occam's Razor to me (but I wish I remembered the argument). There is another school of thought: that if people were to travel back in time and change history, they'd wind up in an alternative universe or in another timeline (and THAT has spawned an entire science fiction subgenre itself).

Some physicists (such as Michio Kaku) have argued that time travel is possible in theory, via means such as wormholes and heating up things so much that wormholes appear. Hawking contends that wormholes would collapse as soon as someone attempts to send light (or information) back in time through it. (And some s.f. authors, such as Stephen Baxter, have tried to cash in on such subjects - "The Light of Other Days", along with time travel stories).

99 Name: Anonymous Scientist : 2007-10-21 23:01 ID:sW+pmhcT

>>98 There is a third option. In some of the Philadelphia Experiments (Scifi or truth? We may never know.) they sent some accomplice back in time to kill the father of some guy, but when the killer came back there was no change in the present. The only thing that changed was that the memory of the father of the guy was somehow fading away.

100 Name: Anonymous Scientist : 2007-10-22 19:19 ID:wvcUGj1x

100 Get

101 Name: Anonymous Layman : 2007-10-22 23:00 ID:VpMuU2/w

With an infinitely powerful telescope and an unending search of the night sky, perhaps one could peek around the corner of a singularity 500 million light years away and see a billion-year old Earth. Just see what it looked like then, of course.

If it were possible to cause changes in the past that affect the present, I'm sure we'd have know about it already due to the swarm of interlopers coming back to give high-fives to us people from the Stupid Ages.

102 Name: Anonymous Scientist : 2007-11-25 08:55 ID:6PACnZ0v

>>101

But what about the possibility that the time machine has to be stationary (a la Ronald Mallett and his "time machine")?

In other words, you don't travel with the time machine like in back to the future, but instead travel TO the time machine at an earlier point in time. This means that it would be impossible to travel back further than when the first time machine existed, because there would be no arrival point.

Meaning, no one from the future can come to this time because a time machine hasn't been invented yet.

(Keep in mind I am basing this off of a documentary I saw a few years ago, so please correct me if I have misrepresented Mr. Mallett's theories).

103 Name: Anonymous Scientist : 2007-11-30 15:57 ID:a4NPZkeb

OK, point on the speed of a tube of ball bearings 10 light second long. It would take approx. 139 hours, assuming the ball bearings are perfectly aligned and made of steel, for the "information" that the first ball bearing moved to reach the last one.

I know the fact it moves at the speed of sound has already been pointed out, I just thought I'd throw a number next to it.

There are two types forces through a median - longitudinal vibrations and transverse vibrations. Since we are compressing the metal bearings, we want longitudinal vibrations. The speed of longitudinal vibrations through steel is about 6000 m/s.

Also, since there seems to have been some misunderstanding...
as long as the ball bearings are all aligned correctly, they behave EXACTLY like a single unit, except for the last one which will pop out.

Interestingly, a cylinder that is infinitely massive would be unable to be compressed, and it seems that the information of a force should be instantaneous through it, right? Not that it would matter, since it could obviously not exist, but still, it's a curious question.

Also, another question. Since light moves at the speed of light (or very, very close to it), from the perspective of the light (if you can imagine such a thing), would the light exist along all of its paths at once, if we ignore any time it hits a medium that slows it down?

104 Name: Anonymous Scientist : 2007-12-02 16:51 ID:TZ2BDyKP

> Interestingly, a cylinder that is infinitely massive would be unable to be compressed, and it seems that the information of a force should be instantaneous through it, right?

You're making the usual mistake here of thinking of a "solid" as something that actually exists. "Solid" is an intuitive shorthand we use for something which is actually very, very different.

Think about what a "solid" actually is: It's a bunch of atoms packed together, sometimes in a crystal lattice. An atom, on the other hand, is a tiny nucleus surrounded by an electron cloud.

What happens when sound is transmitted is that the atoms move, and their electron clouds push up against each other, and repel because they have similar charges. Now you question becomes, what do you mean by "infinitely massive"? Do you have infinitely massive nuclei with normal electron clouds? Do you have an infinite number of nuclei packed into a finite volumes? What happens to the electron clouds then?

And so on. The answer you end up with is that your question is meaningless and unanswerable, because the situation makes no sense physically.

105 Name: Anonymous Scientist : 2007-12-03 00:19 ID:MK0OTpW5

>>104

Now you question becomes, what do you mean by "infinitely massive"? Do you have infinitely massive nuclei with normal electron clouds? Do you have an infinite number of nuclei packed into a finite volumes?
What happens to the electron clouds then?

Quark-gluon plasma.

106 Name: Anonymous Scientist : 2007-12-04 18:38 ID:cTtQmPZW

>>104
Quark star? Isn't that basically "infinitely compressed", such that it is a solid piece of matter, as much as we understand matter to be? A collection of free quarks gathered together to form, essentially, a single particle of a size similar to a neutron star? If so, that material would be, intuitively at least, unable to support shock waves through it.

And though this is somewhat unrelated, isn't the inside of a black hole considered to be infinitely massive and infinitely small by some? I've read that several times, and it seems blatantly wrong, but maybe it is and I'm just not understanding how gravity works.

107 Name: Anonymous Scientist : 2007-12-04 23:15 ID:MK0OTpW5

> isn't the inside of a black hole considered to be infinitely massive and infinitely small by some?

I imagine that's just poetic license taken by some cheap science fiction writer.

108 Name: Anonymous Scientist : 2007-12-05 06:28 ID:tbSEwcZO

>>107
Actually, cheap science books. Not that there is a huge difference...

109 Name: Anonymous Scientist : 2007-12-07 12:10 ID:E4evLiqi

>>106

That would still be entirely finite.

110 Name: Anonymous Scientist : 2007-12-07 23:57 ID:dEIbNI8R

What about 10 dimensions or M theory?

111 Name: Anonymous Scientist : 2007-12-07 23:58 ID:dEIbNI8R

In the year of '39 assembled here the Volunteers
In the days when lands were few
Here the ship sailed out into the blue and sunny morn
The sweetest sight ever seen.
And the night followed day
And the story tellers say
That the score brave souls inside
For many a lonely day sailed across the milky seas
Ne'er looked back, never feared, never cried.
Don't you hear my call though you're many years away
Don't you hear me calling you
Write your letters in the sand
For the day I take your hand
In the land that our grandchildren knew.
In the year of '39 came a ship in from the blue
The volunteers came home that day
And they bring good news of a world so newly born
Though their hearts so heavily weigh
For the earth is old and grey, little darlin' we'll away
But my love this cannot be
For so many years have gone though I'm older but a year
Your mother's eyes from your eyes cry to me.
Don't you hear my call though you're many years away
Don't you hear me calling you
All the letters in the sand cannot heal me like your hand
For my life
Still ahead
Pity Me.

112 Name: Anonymous Scientist : 2007-12-17 05:56 ID:EtkKbyMa

>>103
I recently read somewhere (I don't remember where) that they're toying with the idea of time as a 4th dimension of space. It seems to me to make sense, but in any case, if it is, I don't think I can say yes to "Since light moves at the speed of light (or very, very close to it), from the perspective of the light (if you can imagine such a thing), would the light exist along all of its paths at once, if we ignore any time it hits a medium that slows it down?"

If time were itself a dimension (what could have happened in this universe without it AND the dimensions of space?), I would have to assume that light moves within the dimensions of space (albeit at an incredible rate), according to the laws of time (which is presumably the only truly 'instantaneous' 'thing'). The actual speed time moves at, as opposed to the speeds things move about inside it, is the speed we have to beat to go forwards. Even then, I don't think we could pin-point A time and zap ourselves there. We'd exist in the 3 dimensions of space, going forwards through time quite literally (as one goes forward through time in their day to day lives). Going backwards seems to me, on this basis, impossible.

113 Name: Anonymous Scientist : 2007-12-17 13:30 ID:Heaven

>>112

Time has been considered a fourth dimension of space-time for a hundred years, soon. Note, however, that that is specifically space-time, not space. The spatial dimensions are different from the time dimension, although they together form a whole.

114 Name: Mahuloq : 2007-12-19 07:37 ID:zQsajZBT

What about the 6 other dimensions of space!
http://revver.com/video/99898/imagining-the-tenth-dimension/

115 Name: Anonymous Scientist : 2007-12-20 01:10 ID:Heaven

>>114

I wouldn't worry about them until the spring theorists actually manage to find some actual experimental evidence.

116 Name: Anonymous Scientist : 2007-12-20 15:56 ID:sW+pmhcT

But if time is a dimension then it should mean we can go back in time, and we have seen that it's highly unlikely. Therefore time can't be a dimension... or that it's a special, one-way dimension?

117 Name: Mahuloq : 2007-12-20 20:44 ID:pDElAak7

I have always thought that to defeat that paradox, when you go "back" in time, you are always just traveling to a parallel dimension, therefore no paradox can occur, fine kill the your mum in that universe, your still there and fine.

118 Name: Anonymous Scientist : 2007-12-21 01:33 ID:Heaven

>>116

It is a dimension, but it is a time-like dimension instead of a space-like one. The Minkowski metric, which describes flat space-time, contains ones for the three space-like dimensions, and a -1 for time: http://mathworld.wolfram.com/MinkowskiMetric.html

There is really no explanation for why our universe can be described with such a metric, but it can, and thus we are stuck with three space-like and one time-like dimension.

119 Name: Anonymous Scientist : 2008-01-04 15:53 ID:9AtRNDu8

>>117

i think it's more like this:

You travel back in time. INSTANTLY, just by appearing in the "past" you have changed that universe irrevocably. A paralell universe is the result, you kill your grandpa, you travel forward in time to the present. Everything seems fine, you don't die because you're actually from a paralell universe, but in that universe you never existed. and life goes on. however, it is not your universe anymore, and you never return to the "present" of your own universe. Nor does the history of your universe become altered.

now that i type it all out, though, it does all seem rather arbitrary - is there any proof of paralell universes?

120 Name: Anonymous Scientist : 2008-01-06 01:04 ID:MK0OTpW5

> is there any proof of paralell universes?

Not yet, and there may never be any.

121 Name: Anonymous Scientist : 2008-01-09 18:39 ID:OxZASRqc

Time-travel is indeed possible. We know the mathematics and methods of how to bend time and space. The only problem is our energy constraints. It would take all the energy of our solar system PLUS that of another to actually travel in time.

122 Name: Anonymous Scientist : 2008-01-09 18:56 ID:sW+pmhcT

>>121
So, two portable black holes? Yup, that's what John Titor was/will be using. Created by CERN's Large Hadron Collider in the near furure. Currently scheduled to begin operation in May 2008.

123 Name: Anonymous Scientist : 2008-01-09 20:46 ID:9AtRNDu8

>>122

that's just plain false. The likelihood of creating a black hole is small, like one a second, when considering the scale of time with particle physics. Next, the holes themselves would be too unstable as such a small scale, meaning they won't last, and FINALLY, even if a black whole were to be created, and be able to stick around long enough to acrete the earth, it would evaporate instantly from (they still technically unproven) hawking radiation. If making black holes to destroy the earth was that easy, some jerkass would have done it by now - or the universe would be CONSTANTLY hurling black holes everywhere.

124 Name: Anonymous Scientist : 2008-01-09 20:47 ID:9AtRNDu8

>>122

Addendum:

how would one use black holes to power something?

125 Name: Anonymous Scientist : 2008-01-10 02:31 ID:sW+pmhcT

>>123
No, those mini black holes created by Man would not destroy the Earth. They probably wouldn't even sink below ground, they would evaporate. The actual danger would come from the evaporation point, with plenty of heat and radiations.
Not all black holes are stellar-size-massive. The braneworld theory predicts the existence of tiny black holes seeded throughout the universe, remnants of the Big Bang. And that thousands of them should exist in our solar system.

126 Name: Anonymous Scientist : 2008-01-11 19:11 ID:9AtRNDu8

>>125

that's what i was trying to say, but i guess i forgot to mention they were really tiny, which is important.

127 Name: Anonymous Scientist : 2008-01-11 20:12 ID:sW+pmhcT

Okay. Next, how much energy does a black hole needs to be? If we look at John Tytor's time machine manual, we see in the "Emergency procedures" section: "Unit self-destruct is pilot controlled. The singularities will automatically evaporate with a compromise in the containment field. A nuclear explosion with the equivalent of 2x megatons will detonate upon singularity evaporation."
So we'll need to get the CERN to cram 20-29 megatons of energy into a singularity. Then we'll be able to time travel.

Oh, and incidentally we'll also need to invent that "containment field" first if we don't want the CERN to vanish. So far it doesn't exist yet... :)

128 Name: Anonymous Scientist : 2008-01-20 19:30 ID:QPZM8lgA

>>Not all black holes are stellar-size-massive. The braneworld theory predicts the existence of tiny black holes seeded throughout the universe, remnants of the Big Bang. And that thousands of them should exist in our solar system.

Holy Magnetic Monopoles, Batman! Wasn't this one of Stephen Hawking's predictions from, like, 1972? And hasn't he abandoned it and moved on?

129 Name: Anonymous Scientist : 2008-01-20 22:22 ID:sW+pmhcT

130 Name: Anonymous Scientist : 2008-01-31 10:14 ID:C7FFjEIl

I already figured out time travel. The problem isn't getting to there. It's getting from here.

131 Name: Doctor : 2008-02-01 01:48 ID:Heaven

ummm...

132 Name: Anonymous Scientist : 2008-02-01 04:56 ID:sW+pmhcT

What's strange in those time-travel stories is that "space" is omitted out of the equation. Time and space are very closely related. A time machine should be able to do space traveling. Even John Titor said that the first problem they had with their time machine is that the machine would re-appear elsewhere, and it puzzled the engineers for a while (it was because the Earth is in motion, while the machine wasn't when operating.) Where are all the space travelers' stories?

133 Name: Anonymous Scientist : 2008-02-01 19:57 ID:idwUBqtg

>>132

This is a very insightful comment,... It sometimes pays of to waste time here

A "straight" time jump of even a few seconds would leave you in cold space. But that's assuming that time travel would somehow use a "fixed" referential. But if there is no such thing, there could still be problems, if time translation warps space translation.

You would add teleportation woes to timetravel headaches.

134 Name: Anonymous Scientist : 2008-02-01 23:39 ID:MK0OTpW5

Not only earth is moving, the system and the galaxy are in motion as well.

135 Name: Anonymous Scientist : 2008-02-02 01:50 ID:Heaven

>>132-134
all motion is relative, only acceleration is relevant in this case. also, it's quite possible that earth's gravitational field might cause the time machine to follow earth.

136 Name: Anonymous Scientist : 2008-02-11 15:02 ID:idwUBqtg

>>135

Well,... Time travel could be seen as a form of acceleration in space-time. In which case some of this acceleration might result in the problems mentioned... Or not.

137 Name: Anonymous Scientist : 2008-02-15 01:16 ID:o/K6QW7l

>>132
That is very interesting. If you think of time like a space dimension, then jumping forward or backward in time faster than the rate we are going now, is like traveling faster than light. So a time machine is an FTL drive. Cool.

And FTL drives are like time machines? And time travel is full of paradox, so it is impossible. Therefore faster than light travel is not possible...so much for humanity taking over the galaxy.

Actually come to think of it again...we can assume that time travel into the past is impossible and so warp drives would be like going forward in time really fast. Fini.

138 Name: Anonymous Scientist : 2008-02-15 14:19 ID:QPZM8lgA

>>warp drives would be like going forward in time really fast. Fini.

lolwut

srsly, ever heard of the theory of relativity?

139 Name: Anonymous Scientist : 2008-02-15 15:00 ID:o/K6QW7l

>>138
Theory of relativity only deals with sub-light travel. I can make up whatever the hell I want to wrt faster than light travel.

Anyway, I don't know what you are talking about. Explain please.

140 Name: Anonymous Scientist : 2008-02-15 20:11 ID:GUxM/xdZ

>>139

It's hard enough to get <i>to</i> the speed of light, let alone past it. From the Usenet Physics FAQ:

It is a consequence of relativity that the energy of a particle of rest mass m moving with speed v is given by

      E = mc^2/sqrt(1 - v^2/c^2) 

As the speed approaches the speed of light the energy approaches infinity. Hence is should be impossible to accelerate an object with rest mass to the speed of light and particles with zero rest mass must always go at exactly the speed of light otherwise they would have no energy.

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html

141 Name: Anonymous Scientist : 2008-02-16 11:02 ID:o2Omsbkr

However, none of that explains why time only flows in one direction

142 Name: Anonymous Scientist : 2008-02-16 17:36 ID:o/K6QW7l

>>140
As I said, that only deals with sub-light stuff and using actual down-to-Einstenian-mechanics forces. You can't just use good old classic mechanics when talking about time travel and say oh noes, FTL (faster than light) is impossible.

There could well be a way to "jump" to FTL space and skip the whole energy going to infinity problem. And what I said before was compare going jumping forward (or whatever direction) in space faster than light to jumping forward in time, oh, faster than the current pace time is going. I just never thought of it like that before.

>>141
Time paradox.

143 Name: Anonymous Scientist : 2008-02-16 17:42 ID:enesCUJn

it is possible. If i get a plane to somewhere far away, i'll find myself in tomorow or yesterday, lol.

144 Name: Anonymous Scientist : 2008-02-16 18:24 ID:o2Omsbkr

>>142

>Time paradox.

That's no answer,... You could imagine a boatload of Space paradoxes (ubiquity, or several objects at the same place), none none prevent you from moving in all directions of space.

145 Name: Anonymous Scientist : 2008-02-16 19:57 ID:Heaven

>>As I said, that only deals with sub-light stuff
>>that only deals with sub-light stuff
>>sub-light

PROTIP: Star Trek is fantasy.

146 Name: Anonymous Scientist : 2008-02-16 20:19 ID:dFSPKAAa

>>144

I'm not sure that you can just turn around and move in the opposite direction through time.

Even though time is a dimension, the arrow of time is a consequence of thermodynamics. Since entropy must always increase,
there is an entropy gradient from 'past' to 'future' across the time dimension. Any information-processing device (such as your brain) is subject to the same physical laws as every other object, and increases the total entropy of the universe every time it it performs an operation. So any information-processor must perceive a total increase in entropy through time in one direction only.

This does not preclude the possibility of closed timelike curves.

147 Name: Anonymous Scientist : 2008-02-16 21:08 ID:Heaven

>>145
PROTOP: This is a thread of time travel.

148 Name: Anonymous Scientist : 2008-02-17 01:16 ID:o2Omsbkr

>>146
You bring up the classic point of linking time and entropy. Thats fine with me, except for two things:

We use entropy to the issue because it's one of the rare physical laws which is not symmetric, and could thus explain the perceived irreversibility of time.

However you don't know for instance which one is the consequence of the other, or if they are both the consequence of a third unknown factor, or if they have nothing to do, but are both instances of irreversible effects.

Also, if bidirectional time travel exists, then it would increase entropy in the past, which in turn would increase entropy in the future. If so, there would be no obvious break in the second thermodynamic law when you time travel.

Finally, and as you hint, you must take into account the whole system, when you assay the increase in entropy, and thus local time jumps would be possible at the expence of entropy increase somewhere else in the system. Basically, we don't know the link between irreversibility of time and entropy, so it's a bit difficult to explain one with the other. But it's a good starting point for speculation,...

149 Name: Anonymous Scientist : 2008-02-17 01:56 ID:MK0OTpW5

>>141
How do you know time only flows in one direction, or at all?

150 Name: Anonymous Scientist : 2008-02-17 04:02 ID:o/K6QW7l

>>148
How would local reversal of time work though? I tried imagining it and I just can't come up with anything that makes sense.

One, you can't just hop into a time machine and watch the world outside reverse itself. The world is huge and it will take an immense amount of energy...if it's even remotely possible, what with all the tiny atoms and energy and stuff.

You can have an isolated system though, and forward and reverse the stuff inside from the outside (now idea how, but it makes sense).

But let's say we have a bit of space where time is going in reverse. If you throw a rock (or yourself) in there, how is it going to interact with the space?

151 Name: Anonymous Scientist : 2008-02-17 12:02 ID:FQiRyXDB

>>150

We have trouble understanding time, because we spend all our life immersed in it. It's a bit like air: in the past people did not realised that air is not just space between objects, it's something in itself. Of course there were hints (water/air interface forming bubbles, winds). Nowadays it's much easier to understand air, because we see all the time applications of our knowledge of it (airplanes, etc).

I have no knowledge of reverse-time physics, but it's not a problem in this case, because all your questions equally apply to time flow variations: as you may know, the flow of time you're in depends on the mass surrounding you and on your speed.

So if you are travelling at close to the speed of light, your time will be very different from all surrounding objects which travel at a slower speed. As you can see, you can induce a local variation in the flow of time without requiring infinite amounts of energy. One could extend the reasoning and assume that you can vary the local flow of time to such an extent, that you might locally revert it. The conceptual difficulties are the same in both cases.

As for your question with the rock, you just have to think about black holes. In a black hole the mass is infinite, and the flow of time is ripped apart (and I think nobody knows what's going on inside a blackhole). So if you throw a rock into the black hole, as the rock travels space, the flow of time it is subjected to will slow down until it reaches singularity, and then it's anyone's guess. Some people have even suggested that matter could emerge in other points of space or time through white holes (it's not only time which is ripped apart, but space too).

152 Name: Anonymous Scientist : 2008-02-17 12:06 ID:FQiRyXDB

>>151

Oops, I meant to say 'In a black hole the mass DENSITY is infinite,...'

153 Name: Anonymous Scientist : 2008-02-17 17:16 ID:o/K6QW7l

>>151
In my previous post, I was thinking of time as a consequence of the movement of matter and energy but that's not the case obviously, space-time and all that. So you wouldn't need infinite energy to change your perception of time outside you (or your frame of reference). You need to somehow change your frame of reference so that the outside world is reversing to you. Argh, I need to properly understand special relativity to actually begin to make a guess at this.

154 Name: Anonymous Scientist : 2008-02-17 17:21 ID:CrGUsWlF

>>152
Not necessarily. In order for it to be defined as a black hole, the mass density need only be sufficient that light cannot escape.

155 Name: Anonymous Scientist : 2008-02-17 18:27 ID:FQiRyXDB

>>154

We are both right, but at different time points,... You are right that mass density does not need to be infinite to CREATE a black hole (otherwise you'd need infinite amounts of matter and there would be no black holes). What really counts is the amount of matter bound by the gravity well. If this amount is enough to cause collapse and a singularity to occur (a black hole), then the mass density will become infinite. This is why it's called a singularity: all the mass collapsed to a single point in space, the singularity, hence mass density is infinite.

All black holes have the same mass density (infinite), what differs is the amount of mass contained within the singularity. The higher the amount of mass, the wider the event horizon (distance from which light cannot escape the black hole).

156 Name: Anonymous Scientist : 2008-02-18 12:48 ID:sf6Yn2sp

>>153

Special relativity won't get you much. You need general relativity, and that actually intuitively understanding that may require being insane.

On the topic of time and entropy, though, I recently saw the suggestion made that maybe time itself is only a macroscopic property. That would go some way towards explaining why it's so incredibly hard to define a direction of time from the microscopic theories.

What exactly that would mean in practice sure is food for thought, but without a functioning quantum theory of gravity it may be impossible to even speculate.

157 Name: Anonymous Scientist : 2008-02-18 16:15 ID:idwUBqtg

>On the topic of time and entropy, though, I recently saw the suggestion made that maybe time itself is only a macroscopic property.

Hard to accept that,... Gravity does not play a role at microscopic scales, but space and time do. Particle accelerators show relativistic effects on time affecting the particles. So it seems it's sleight of hand to suddently consider time a macroscopic property.

158 Name: Anonymous Scientist : 2008-02-19 10:03 ID:CrGUsWlF

>>157
That, and also many kinds of subatomic particles have measurable half-lives which are extended by relativistic travel. This seems to contradict the idea that time is a macroscopic property only.

159 Name: Anonymous Scientist : 2008-02-19 14:19 ID:E4evLiqi

I think that was more specifically the direction of time being a macroscopic effect, or the flow of time.

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