Wormhole time machine debunked
Christopher M. Jones
use a wormhole as a time machine due to the "twin paradox".
In essence, you accelerate one end of a wormhole or put it
next to a large mass and wait a little bit and then that
end of the wormhole will be "absolutely younger" than the
other end of the wormhole, thus creating a time machine.
I've always thought this was a bit faulty, and now that
I think about it more I can say that it is.
For example, the Earth and Moon have been in different
gravitational fields (slightly), and yet you can travel
to and from the Moon without going into the past.
Merely because space-time or an object is "younger" than
another region or object does not mean that going from one
to the other sends you into the past or into the future.
The twin paradox itself shows the resolution of the
"time travel problem" because even though one twin is
younger than the other twin (after accelerating or what-
have-you) they can still meet and shake hands, the
"younger" twin is not perpetually stuck in the older
twin's past.
Now, as to the whole FTL travel causality violation thing,
that's a different story (and one that I don't think has
been completely understood yet).
Geoffrey A. Landis
> ...
> Merely because space-time or an object is "younger" than
> another region or object does not mean that going from one
> to the other sends you into the past or into the future.
That's right. You can only do this IF you can travel faster than light.
Traveling to another place SLOWER than light won't give you time travel.
> The twin paradox itself shows the resolution of the
> "time travel problem" because even though one twin is
> younger than the other twin (after accelerating or what-
> have-you) they can still meet and shake hands, the
> "younger" twin is not perpetually stuck in the older
> twin's past.
>
> Now, as to the whole FTL travel causality violation thing,
> that's a different story
Wormholes ARE FTL travel. That's the whole point.
> (and one that I don't think has been completely understood yet).
Right.
--
Geoffrey A. Landis
author of MARS CROSSING
http://www.sff.net/people/geoffrey.landis
Aaron Bergman
>
> Merely because space-time or an object is "younger" than
> another region or object does not mean that going from one
> to the other sends you into the past or into the future.
> The twin paradox itself shows the resolution of the
> "time travel problem" because even though one twin is
> younger than the other twin (after accelerating or what-
> have-you) they can still meet and shake hands, the
> "younger" twin is not perpetually stuck in the older
> twin's past.
No. What happens is that you send the wormhole out on a long
round trip at relativistic speeds. Then, one of the wormhole
experiences more time than the other. You can use this to
literally travel to the past. The key is that at the end, the
wormhole mouths are right next to each other.
Aaron
--
Aaron Bergman
<http://www.princeton.edu/~abergman/>
Christopher M. Jones
> No. What happens is that you send the wormhole out on a long
> round trip at relativistic speeds. Then, one of the wormhole
> experiences more time than the other. You can use this to
> literally travel to the past. The key is that at the end, the
> wormhole mouths are right next to each other.
Sheesh, did you read my post? That idea is just plain
nonsensical. Take a long piece of twine, take one end and
accelerate it or whatever so that it experiences high time
dilation relative to the other end. Now, put the two ends
together, one end is younger than the other. Does that
mean that the younger end is in the past of the older end?
ABSOLUTELY NOT! If an ant crawls along the twine from the
old end to the young end it DOES NOT travel backward in
time, it simply travels from older twine to younger twine.
See?
--
I am not a hyper intelligent kangaroo mouse pelt hat, sorry for the
confusion.
George William Herbert
Wormholes are not twine. If the ant could run around the circumfrence
of the twine infinitely fast, it would come out in the same time
frame as the "younger" end of the twine.... in the local past.
That's the point... once you start combining relativity time
distortions with unlimited FTL, you get to do things like that,
because the time path doesn't necessarily monotonically increase.
-george william herbert
gher...@retro.com
Geoffrey A. Landis
"Christopher M. Jones" wrote:
>
> "Aaron Bergman" <aber...@princeton.edu> wrote:
> > No. What happens is that you send the wormhole out on a long
> > round trip at relativistic speeds. Then, one of the wormhole
> > experiences more time than the other. You can use this to
> > literally travel to the past. The key is that at the end, the
> > wormhole mouths are right next to each other.
>
> Sheesh, did you read my post? That idea is just plain
> nonsensical.
Aaron, this guy has to be a troll-- his initial post made it look like
he was merely confused, but with this second post, it's hard to believe
that he could really be *this* clueless.
--
Geoffrey A. Landis
http://www.sff.net/people/geoffrey.landis
Erik Max Francis
> Sheesh, did you read my post? That idea is just plain
> nonsensical. Take a long piece of twine, take one end and
> accelerate it or whatever so that it experiences high time
> dilation relative to the other end. Now, put the two ends
> together, one end is younger than the other. Does that
> mean that the younger end is in the past of the older end?
> ABSOLUTELY NOT!
If the two ends of the twine were adjacent to each other in spacetime,
then it would. Which is exactly what happens in a wormhole.
Reality check: People who know far more about general relativity than
you (or I) have thought long and hard about this and have demonstrated
mathematically that it must happen if general relativity is correct and
wormholes are possible. Your objection is that it does not make sense
to you. That, unfortunately, is not a good indication of whether or not
an idea, coming from a complicated mathematical theory, is actually
correct.
Special relativity requires only high school algebra, and yet many
cranks do not understand it, and thus declare it wrong. Be careful
falling into the same trap. "I do not understand X" is not the same
thing as "X is nonsensical and fundamentall flawed" or "X is logically
inconsistent."
--
Erik Max Francis / m...@alcyone.com / http://www.alcyone.com/max/
__ San Jose, CA, US / 37 20 N 121 53 W / ICQ16063900 / &tSftDotIotE
/ \ It is much safer to obey than to rule.
\__/ Thomas a Kempis
Erik Max Francis' bookmarks / http://www.alcyone.com/max/links/
A highly categorized list of Web links.
pervect
"Geoffrey A. Landis" <Geoffre...@sff.net> wrote in message
news:3A5B608A...@sff.net...
He could be a "anti-relativist", seems we have a lot of them around recently
(or maybe just one using different names to make it look like there are
more).
Christopher M. Jones
What? First off, Mr. Bergman's post added (from what I
could tell) absolutely nothing and made me indeed wonder
if he had read my original post.
Now, as to the merits of the argument, that's a different
story. I have yet to hear any more detailed description
of the "wormhole timemachine" phenomenon other than the
old twin paradox w/ the endpoints spiel. Maybe I'm
confused and there's something I'm missing or I'm over
interpreting into the popular generalization (which might
very well be the case) but it seems like there's something
funky going on.
The popular generalization that I've heard is that you
take one terminus of a wormhole, do something relativistic
with it in such a way that it ages less than the other end
then when you travel from the older terminus to the younger
terminus you travel back in time. Now, to me, this clearly
seems to be bunk. Somewhat of a confusion between "age" and
"time".
However, I think that perhaps the preceeding scenario is
really just a horribly flubbed attempt at explaining the
causality violations that can occur with FTL travel (i.e.
getting back into your own light cone and what not). If
so, then that makes a whole lot more sense.
--
All I wanted was a pepsi, just one pepsi.
Christopher M. Jones
> "Christopher M. Jones" wrote:
>
> > Sheesh, did you read my post? That idea is just plain
> > nonsensical. Take a long piece of twine, take one end and
> > accelerate it or whatever so that it experiences high time
> > dilation relative to the other end. Now, put the two ends
> > together, one end is younger than the other. Does that
> > mean that the younger end is in the past of the older end?
> > ABSOLUTELY NOT!
>
> If the two ends of the twine were adjacent to each other in spacetime,
> then it would. Which is exactly what happens in a wormhole.
>
> Reality check: People who know far more about general relativity than
> you (or I) have thought long and hard about this and have demonstrated
> mathematically that it must happen if general relativity is correct and
> wormholes are possible. Your objection is that it does not make sense
> to you. That, unfortunately, is not a good indication of whether or not
> an idea, coming from a complicated mathematical theory, is actually
> correct.
First off, I am the last person to claim that relativity is
bunk, and I am not claiming that. I was calling into question
the merits of (what seemed to me to be) a poorly thought out
and poorly "researched" popular generalization.
> Special relativity requires only high school algebra, and yet many
> cranks do not understand it, and thus declare it wrong. Be careful
> falling into the same trap. "I do not understand X" is not the same
> thing as "X is nonsensical and fundamentall flawed" or "X is logically
> inconsistent."
It does seem to me that the idea of "end B of the wormhole is
younger than end A of the wormhole" leading to "travelling from
end A to end B goes back in time" is logically inconsistent.
For example, an object on the Earth (due to relativistic effects)
will be several years younger (taking into account all the time
dilation from about 5 billion years ago) than an object out at
the orbit of Jupiter (say a Trojan asteroid). However,
travelling from the asteroid to Earth (and hence through the
space between them that is continuously "younger and younger")
you do not go backward in time. The same would seem to apply
for a wormhole with one end "younger" than the other.
Perhaps there is some key concept along the way that I have
failed to grasp or something, and I have no better or more
complete explanation of "what goes on" than the basic twin
paradox "one end is younger" explanation. I would greatly
appreciate it if someone could in fact provide a more complete
explanation (with Minkowski diagrams and what-not) of just
exactly why I am wrong (if I am wrong).
--
We know about the bodies stacked in your crawlspace
Aaron Bergman
M. Jones" <christ...@uswest.net> wrote:
> Now, as to the merits of the argument, that's a different
> story. I have yet to hear any more detailed description
> of the "wormhole timemachine" phenomenon other than the
> old twin paradox w/ the endpoints spiel. Maybe I'm
> confused and there's something I'm missing or I'm over
> interpreting into the popular generalization (which might
> very well be the case) but it seems like there's something
> funky going on.
OK. Imagine clocks at both ends of the wormhole. Take one end out
at relativistic speeds. Ask yourself, in your scenario, what the
person sees when looking at the clock through the wormhole and
compares it to his own clock. What if he were to reach through
the wormhole and grab it? One can see that this quickly becomes
untenable.
The only reasonable answer is that both clocks always read the
same because you can have them arbitrarily close to eachother.
Still, when you get back to the beginning, the person on earth
must have lived longer than you, so his clock must be at a longer
time. So, the wormhole must reach into the past.
Erik Max Francis
> First off, I am the last person to claim that relativity is
> bunk, and I am not claiming that. I was calling into question
> the merits of (what seemed to me to be) a poorly thought out
> and poorly "researched" popular generalization.
Wormholes have been discussed in scientific papers in quite a bit of
detail, they are not "popular generalizations." They may not be
physical, but they are certainly consistent with general relativity.
> Perhaps there is some key concept along the way that I have
> failed to grasp or something, and I have no better or more
> complete explanation of "what goes on" than the basic twin
> paradox "one end is younger" explanation. I would greatly
> appreciate it if someone could in fact provide a more complete
> explanation (with Minkowski diagrams and what-not) of just
> exactly why I am wrong (if I am wrong).
The key element you're missing is that the two ends of the wormhole
represents disparate events which in addition to being separated by
whatever space _and time_ outside the wormhole path (caused by whatever
trip you take one end of the wormhole on), are also adjacent to each
other in spacetime by the nature of the wormhole connection itself.
If you take one end of the wormhole on a relativistic journey and bring
it back, it comes back "younger" -- but by that it represents, if you
will, an event in spacetime in the past (because it came back younger).
The thing you're missing is that since these two ends are adjacent
through the wormhole, if I walk through the end which stayed home, I
_must_ come back through the other end _in the past_. The thing that
makes it different is the wormhole itself, which you seem to be looking
past.
--
Erik Max Francis / m...@alcyone.com / http://www.alcyone.com/max/
__ San Jose, CA, US / 37 20 N 121 53 W / ICQ16063900 / &tSftDotIotE
/ \ All the people in my neighborhood turn around and get mad and sing
\__/ Public Enemy
The laws list / http://www.alcyone.com/max/physics/laws/
Laws, rules, principles, effects, paradoxes, etc. in physics.
Geoffrey A. Landis
goes like this:
"People argue that wormholes could allow time travel. But if you have a
piece of string, and you travel from one end to another, and you don't
go faster than light, you can't go back in time."
OK, yeah, so? A wormhole is not a piece of string. Traveling through a
wormhole is not like traveling along a piece of string.
specificially, you wrote:
> If an ant crawls along the twine from the
> old end to the young end it DOES NOT travel backward in
> time, it simply travels from older twine to younger twine.
A wormhole is not like string. An ant crawling along a piece of string
is still travelling in a simply-connected manifold. A wormhole is not
like crawling along string; it is a multiply connected spacetime.
You say that this "debunks" wormholes, and you say insult Bergman for
saying otherwise, but in essence, about the best that can be said for
your argument is that it makes no sense.
Now, it is not at all obvious why you should be able to turn a wormhole
into a time machine by this technique-- it can be a difficult
transformation to follow unless you make a point of following the math
instead of trying to intuit the answer from "common sense". But
incorrect analogies won't get you there.
Geoffrey A. Landis
> > Perhaps there is some key concept along the way that I have
> > failed to grasp or something,
Right.
EFM has it correctly explained. The key fact is that there are two
different ways to get from one wormhole mouth to the other, and these
paths are *not* reducable. Thus, there are two *different* ways to
measure the distance between the two points-- one way the two points are
an inch apart; the other way they could be light years apart.
A second key fact is that you can't trust common sense; you have to do
the math step by step.
And a third key fact is that we are talking about space-time here, not
just space. You have to specify all coordinates in space and time.
Now, walk through the math. Assume that at each mouth of the wormhole
you have a person with a clock. The two mouths of the wormholes start
out next to each other, and the two people can look at each other and
verify that the two clocks are reading the same. Then they can look at
each other through the wormhole, and verify that their clocks are
reading the same when they compare that way, too.
Note that there is no prefered frame. It is *just* as valid for them to
compare watches through the wormhole as it is for them to compare
watches through external space.
From relativity, you have a formula that tells you how time varies.
Time varies with velocity. In particular, if two people are not moving
with respect to each other, time flows at the same rate.
(You might object that there is another term: time also varies with
gravitational potential. You can integrate the gravitational field to
find the potential between them, and therefore the different rate of
time. Since there is no gravitational field between them, their two
clocks are running at the same rate. So you can ignore this effect.)
Got it so far? OK. Now pick up one wormhole mouth, and the person
standing next to it with her clock, and accelerate it to .995% of the
speed of light (picked for a time dilation of exactly 10, making
calculation easier for me.) The two people are watching each other
through the wormhole. They are not moving with respect to each other
(viewed through the wormhole), so there is no Lorentz time-dilation.
There is no gravitational field going through the wormhole, so there is
no gravitational time dilation. Their clocks are running at the same
speed. A day later, one of them looks at the her watch (it's a day/date
watch) and then looks at the other and says "I read one day elapsed time
exactly," and the other one says, "one day, check." Their time is
exactly synchronized. They continue to do this for the whole course of
the experiment.
In fact, if they want to, they can pass clocks back and forth between
them, so they can set the two clocks next to each other and verify that
they're the same.
Now let's look at the same event through the outside world. They are
now separating at a rate of 0.995 light years per year, of course, so it
is much more difficult for them to compare watches. Without going
through the tedious details, special relativity tells us the answer,
which is that observer A sees observer B as having a watch which is
going at one-tenth speed, and observer B sees observer A as having a
watch going at one-tenth speed. There's no paradox involved; I presume
you understand special relativity to understand this and the reason for
it's not a paradox?
After they have separated by a distance of one light year, measured
through external space, or a distance of zero, measured through the
wormhole (remembering that measured through the wormhole they are not
moving with respect to each other), they stop the (external) motion.
How do their clocks read now?
Looking through the wormhole, their clocks are still *exactly*
synchronised. This is important: in the space through the wormhole,
they never moved with respect to each other. In the space outside the
wormhole, however, they are now both at rest, and two people at rest
with respect to each other can conmpare their clocks. They compare
their clocks (this takes a year to do, since they are a light year
apart), and the observer who moved agrees that her clock is reading way
slow compared the "stationary" observer's clock. (or, as she puts it
equally truthfully, his watch is way fast). This is just special relativity.
Following so far? Now, which one is right? Looking through the
wormhole, their two clocks are synchronized; looking outside the
wormhole, the two clocks differ by 0.9 years. But it's the SAME two clocks.
This is weird, but there's a two-year round-trip light delay in their
conversation. To eliminate this light delay and check the clocks out
directly, the person who had originally moved ('moved' measured in space
outside the wormhole, of course; she had been stationary the whole time
measured through the wormhole) decides to go back. The wormhole
accelerates back to 99.5% of the speed of light. They continue to watch
each other through the wormhole, and they continue to agree that their
two clocks read the same. As they should, since they are not moving
with respect to each other (looking through the wormhole).
So the moving (viewed externally) observer comes back to the start, and
stops. OK, what do their clocks read now? Through the wormhole, their
clocks read the same. Through the outside world, the clock that had
been on the moving wormhole reads 1.9 years slower. BUT THEY ARE THE
SAME TWO CLOCKS: they can't be both synchronized, and also NOT
synchronized.
For convenience, we'll say that the moving (viewed through external
space) observer spent no time at one light year; the instant she reached
a distance of one light year she turned around. It took her only a
month and a quarter, measured in her time, to get there (because of time
dilation); it takes her another tenth of a year to get back, and her
clock/calender reads 0.2 years when she arrives.
The observer who had been on the moving wormhole looks through the
wormhole, says "the clocks are synchronized", then looks through outside
space and sees that the stationary observer's clock reads 2.01 years.
OK, what's wrong here?
She looks over (not going through the wormhole) to the stationary
observer, who is, in fact, standing right next to her, since she's back
home now. She looks at his clock: 2.01 years. Well, that makes sense,
she traveled 2 light years at 0.995 c; it takes 2.01 years to do it.
She looks back at the wormhole, looks through it, and the clock there
reads 0.201 years. So she walks through through the wormhole, looks at
the clock again, and yep, the clock reads 0.201 years, same as hers (as
it should, since they have always been synchronized). So she asks the
guy standing with the clock, what's the deal, I'm back , what's with the
clock? And the guy standing with his clock says, no, you aren't back
yet, you won't be back for another 1.8 years. Look at the clock; you've
only been traveling for 0.2 years; you won't get there for another 0.8
years. She asks the guy how old he is. He just exactly turned 30 (say)
on he day she left; she asks him exactly how old he is now, and he says
"thirty years and 73 days days".
So she looks back through the wormhole, the guy standing there has a
clock is reading 2.01 years. She asks him how old he is now, and he
says "thirty-two years and a few days".
Wim Benthem
wrote:
>If you take one end of the wormhole on a relativistic journey and bring
>it back, it comes back "younger" -- but by that it represents, if you
>will, an event in spacetime in the past (because it came back younger).
>The thing you're missing is that since these two ends are adjacent
>through the wormhole, if I walk through the end which stayed home, I
>_must_ come back through the other end _in the past_. The thing that
>makes it different is the wormhole itself, which you seem to be looking
>past.
So if you went through the wormhole, would you come out before you got
in?
Wim Benthem
Geoffrey A. Landis
>
> So if you went through the wormhole, would you come out before you got
> in?
If the other end of the wormhole is in the past, yes. That's the
definition of "past".
--
Geoffrey A. Landis