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Suppose you have two trains of the same length travelling on the same
track on opposite directions, towards each other.
In the middle the track splits into a double track for a certain distance,
but this distance is slightly smaller than the length of either train.
The task is to make the trains pass each other so that they can continue
their journey.
The trains cannot be split and you can't remove anything from the trains.
The track cannot be modified, and you cannot build additional track.
--
- Warp
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Warp wrote:
> Suppose you have two trains of the same length travelling on the same
> track on opposite directions, towards each other.
>
> In the middle the track splits into a double track for a certain distance,
> but this distance is slightly smaller than the length of either train.
>
> The task is to make the trains pass each other so that they can continue
> their journey.
>
> The trains cannot be split and you can't remove anything from the trains.
> The track cannot be modified, and you cannot build additional track.
Suppose your trains are being driven by brains in jars, and on each of
the paths is a railway worker which will be inevitably killed if a train
is set to that path...
--
Tim Cook
http://empyrean.digitalartsuk.com
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PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
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Warp nous apporta ses lumieres en ce 2008/01/01 12:13:
> Suppose you have two trains of the same length travelling on the same
> track on opposite directions, towards each other.
>
> In the middle the track splits into a double track for a certain distance,
> but this distance is slightly smaller than the length of either train.
>
> The task is to make the trains pass each other so that they can continue
> their journey.
>
> The trains cannot be split and you can't remove anything from the trains.
> The track cannot be modified, and you cannot build additional track.
>
Apply the breaks on the engines as they near the end of the crossing area. The
couplings will contract enough for each trains to clear the end of the other.
Timing will be critical.
--
Alain
-------------------------------------------------
Eat one live toad the first thing in the morning and nothing worse will happen
to you the rest of the day.
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Alain <ele### [at] netscape net> wrote:
> Apply the breaks on the engines as they near the end of the crossing area. The
> couplings will contract enough for each trains to clear the end of the other.
Nope. The trains are too rigid and the difference in length too large
for that to work.
--
- Warp
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"Warp" <war### [at] tagpovrayorg> a écrit dans le message de news:
477a74b0@news.povray.org...
> Suppose you have two trains of the same length travelling on the same
> track on opposite directions, towards each other.
>
> In the middle the track splits into a double track for a certain
> distance,
> but this distance is slightly smaller than the length of either train.
>
> The task is to make the trains pass each other so that they can continue
> their journey.
>
> The trains cannot be split and you can't remove anything from the trains.
> The track cannot be modified, and you cannot build additional track.
>
> --
> - Warp
If the trains' speeds are close enough to the speed of light, because of
relativistic length contraction (and with correct timing) the trains will
have enough length to pass each other on the double track?...
Did I get it? :-p
Xavier
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Xavier Manget <NOS### [at] freefr> wrote:
> If the trains' speeds are close enough to the speed of light, because of
> relativistic length contraction (and with correct timing) the trains will
> have enough length to pass each other on the double track?...
> Did I get it? :-p
Yes.
(Had you heard of the thought experiment, or did you figure it out on
your own?)
--
- Warp
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Warp wrote:
> Xavier Manget <NOS### [at] freefr> wrote:
>> If the trains' speeds are close enough to the speed of light, because of
>> relativistic length contraction (and with correct timing) the trains will
>> have enough length to pass each other on the double track?...
>
>> Did I get it? :-p
>
> Yes.
>
> (Had you heard of the thought experiment, or did you figure it out on
> your own?)
>
Did you, or the person that came up with this idea, actually do the math
for these three reference systems? just curious.
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Warp wrote:
> Xavier Manget <NOS### [at] freefr> wrote:
>> If the trains' speeds are close enough to the speed of light, because of
>> relativistic length contraction (and with correct timing) the trains will
>> have enough length to pass each other on the double track?...
>
>> Did I get it? :-p
>
> Yes.
>
> (Had you heard of the thought experiment, or did you figure it out on
> your own?)
I'm skeptical. The version that I read involved a king and a large
piece of lumber that was longer than the Great Hall and a wager about it
fitting between the two doors, using relativity to boil down to
*appearing* to fit in the hall, saying nothing about actually changing
dimensions.
--
Tim Cook
http://empyrean.digitalartsuk.com
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------
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andrel <a_l### [at] hotmailcom> wrote:
> Did you, or the person that came up with this idea, actually do the math
> for these three reference systems? just curious.
Not me, but the math has been done, of course.
From the reference point of the track, both trains contract by a
certain amount and can pass each other on the double track.
From the reference point of one of the trains the double track is
contracted, but the other train is contracted even more. From this
reference point the other train is so short that it travels the double
track in the same time as this train.
--
- Warp
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Tim Cook <z99### [at] bellsouthnet> wrote:
> I'm skeptical. The version that I read involved a king and a large
> piece of lumber that was longer than the Great Hall and a wager about it
> fitting between the two doors, using relativity to boil down to
> *appearing* to fit in the hall, saying nothing about actually changing
> dimensions.
Relativistic contraction is not a simple optical illusion. It is a
true physical contraction.
If you think that it's only an optical illusion then the train track
thought experiment will seem counterintuitive and impossible. However,
AFAIK if relativity is right, the trains do indeed pass each other
without colliding. It's not only an optical illusion, but a true
contraction.
The thought experiment is mentioned here:
http://en.wikipedia.org/wiki/Ladder_paradox#Relativistic_trains_passing
--
- Warp
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"Warp" <war### [at] tagpovrayorg> a écrit dans le message de news:
477abc37@news.povray.org...
> Xavier Manget <NOS### [at] freefr> wrote:
>> If the trains' speeds are close enough to the speed of light, because of
>> relativistic length contraction (and with correct timing) the trains
>> will
>> have enough length to pass each other on the double track?...
>
>> Did I get it? :-p
>
> Yes.
>
> (Had you heard of the thought experiment, or did you figure it out on
> your own?)
I figured it out on my own :-) ... I've learned a little about special
relativity at school (20 years ago) but I really don't feel comfortable with
it, I find it so counter-intuitive...
Xavier
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Xavier Manget <NOS### [at] freefr> wrote:
> I figured it out on my own :-) ... I've learned a little about special
> relativity at school (20 years ago) but I really don't feel comfortable with
> it, I find it so counter-intuitive...
There's too much physical evidence to support relativity that it's just
impossible to deny that it gets at least pretty damn close to how the
universe really works.
Given the right circumstances I'm convinced that this thought experiment
could indeed work in reality. (Of course it couldn't be done with actual
trains, but something similar could work.)
--
- Warp
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Warp wrote:
> Not me, but the math has been done, of course.
I was wondering about that.
> From the reference point of one of the trains the double track is
> contracted, but the other train is contracted even more. From this
> reference point the other train is so short that it travels the double
> track in the same time as this train.
But the conductor of the eastbound train will see the westbound train
get onto the tracks later than he does, and vice versa. I'll believe the
math was done, but I wouldn't necessarily believe this is a solution
without anyone competent having done the math. :-)
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Warp wrote:
> There's too much physical evidence to support relativity that it's just
> impossible to deny that it gets at least pretty damn close to how the
> universe really works.
It's funny how many people won't deny something unintuitive like quantum
mechanics or relativity, stuff that's really hard to understand properly
even *with* math, but they're happy to deny the possibility of
evolution, which is easy to explain without any mathematics.
As one poster recently repeated here, "f'ed up world!"
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Darren New wrote:
> But the conductor of the eastbound train will see the westbound train
> get onto the tracks later than he does, and vice versa.
Actually, I meant to say "may see" there. And it looks like based on
that wikipedia article that the conductor will actually see the other
train get to its junction *before* he gets to his own. Very strange.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Darren New <dne### [at] sanrrcom> wrote:
> It's funny how many people won't deny something unintuitive like quantum
> mechanics or relativity, stuff that's really hard to understand properly
> even *with* math, but they're happy to deny the possibility of
> evolution, which is easy to explain without any mathematics.
That may be because we can check the theory of relativity here and
now, but we can't go back in time a few million years to check evolution
nor we can perform evolutionary experiments which require a few millions
of years.
--
- Warp
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Warp wrote:
> Xavier Manget <NOS### [at] freefr> wrote:
>> If the trains' speeds are close enough to the speed of light, because of
>> relativistic length contraction (and with correct timing) the trains will
>> have enough length to pass each other on the double track?...
>
>> Did I get it? :-p
>
> Yes.
>
> (Had you heard of the thought experiment, or did you figure it out on
> your own?)
Oh, wait, I thought this was a real-world situation. Silly me.
Regards,
John
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Warp nous apporta ses lumieres en ce 2008/01/02 15:53:
> Darren New <dne### [at] sanrrcom> wrote:
>> It's funny how many people won't deny something unintuitive like quantum
>> mechanics or relativity, stuff that's really hard to understand properly
>> even *with* math, but they're happy to deny the possibility of
>> evolution, which is easy to explain without any mathematics.
>
> That may be because we can check the theory of relativity here and
> now, but we can't go back in time a few million years to check evolution
> nor we can perform evolutionary experiments which require a few millions
> of years.
>
There have been some evolutionary experiments that have been done. Some using
mice, others using insects. Take a mice colony and have it live in a lightless
environment, another in a chilly one, a third in a very hot one, a fourth in a
place where possible living area are far from food sources. Another one
prevented females from copulating for an increasing time.
Do the experiment over a few decades (some are still going on after over a century).
In the dark environment you get mice with atrophied eyes, longer wiskers and
larger ears, and a high albinism incidence.
In the cold, you get longer hairs, increased body fat, short tails and smaller ears.
In the heat, shorter hairs, slightly longer and spindly paws.
The ones that had to travel a lot devoloped longer, stronger legs, larger
stomach. They also devoloped hamster like cheeks.
In the last case, the longevity increased very significantly! Increases in the
order of +200 to 300% to the life span! We are now doing that experiment in a
very large scale: The whole Human Western and Asian populations! Asia, Europe,
the Americas, parts of Africa and Oceanya. From the middle ages to now,
generation time went from about 15 to 16 years to over 30~33 years...
Those are called "forced evolution experiments". The key is to use speciment
that have a short generation time.
--
Alain
-------------------------------------------------
There will always be beer cans rolling on the floor of your car when the boss
asks for a ride home from the office.
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Warp wrote:
> That may be because we can check the theory of relativity here and
> now,
99.44% of the world cannot - they accept the word of experts. And we
can check the theory of evolution here and now - it has been done
repeatedly.
> but we can't go back in time a few million years to check evolution
Sure we can. That's what fossils are for. Same way we check things like
binary stars obeying GR and black holes obeying GR.
> nor we can perform evolutionary experiments which require a few millions
> of years.
Nor can we perform GR experiments that require a few millions of years,
like noticing that the expansion of space seems to be accelerating, or
that light traveling long distances thru space doesn't travel at 'c' for
all the different frequencies.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > That may be because we can check the theory of relativity here and
> > now,
> 99.44% of the world cannot - they accept the word of experts.
It depends on the subject. When the experts say, for example, that they
have to take GR equations into account for GPS to work, that just using
Newtonian laws would not be enough, then sure, you just have to take their
word for it, but it's quite improbable that they are all lying. You can
go and buy a cheap GPS device and check that it works. Now you either
accept that it works correctly because of those GR equations, or you claim
that all the experts are lying. There's no reason why they would do the
latter.
This is an example of a measurement which we can do right here right now.
It doesn't require humongous amounts of time.
As for things like the expansion of the universe, it's a lot more of a
hypothesis. The current consensus among scientists is that the universe
is expanding, but without the millions of years of measurements it's a
lot more of guesswork. I don't believe science says otherwise.
There's a difference between saying "I believe scientists when they say
that GPS needs GR equations to work correctly" and "the current consensus
among scientists is that the universe is expanding". There's a categorical
difference between these two.
Now, if I say "the current consensus among scientists is that the theory
of evolution is mostly correct", that doesn't mean I have the same degree
of confidence in it as with the GPS thing.
> And we
> can check the theory of evolution here and now - it has been done
> repeatedly.
In the exact same way as we cannot check how the expansion of the
universe has occurred during millions of years, we cannot check how
evolution has occurred during millions of years. We can speculate from
some of the consequences, but it's only speculation. We cannot measure
here and now.
> > but we can't go back in time a few million years to check evolution
> Sure we can. That's what fossils are for. Same way we check things like
> binary stars obeying GR and black holes obeying GR.
Says the person who takes expansion of the universe and dark energy
with a grain of salt, and seriously considers alternative theories...
--
- Warp
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John VanSickle <evi### [at] hotmailcom> wrote:
> Oh, wait, I thought this was a real-world situation. Silly me.
Given the proper circumstances (not actual trains, but something similar,
capable of doing the feat), why wouldn't it be a real-world situation?
Or are you saying that relativity doesn't work in the real world?
--
- Warp
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Warp wrote:
> This is an example of a measurement which we can do right here right now.
> It doesn't require humongous amounts of time.
Yep.
> Now, if I say "the current consensus among scientists is that the theory
> of evolution is mostly correct", that doesn't mean I have the same degree
> of confidence in it as with the GPS thing.
Yeah, until you get drug-resistant TB. Then you're kind of screwed.
> In the exact same way as we cannot check how the expansion of the
> universe has occurred during millions of years, we cannot check how
> evolution has occurred during millions of years. We can speculate from
> some of the consequences, but it's only speculation. We cannot measure
> here and now.
Fair enough. But you're not checking that GR worked for millions of
years. You can't check that *any* theory has been correct for millions
of years. It's nothing specific to evolution.
You can watch evolution and speciation in the lab. You can cause it to
happen at will. You can see millions of years of results consistent with
evolution, from bone shape to genetics. You can prove that bone shape
is *caused* by genetics.[1] You have to account for it when creating
medicines. Software and hardware you use daily is designed with
evolutionary algorithms.
Not sure how you can't measure "here and now" what evolution does.
What part do you think is in doubt?
>>> but we can't go back in time a few million years to check evolution
>
>> Sure we can. That's what fossils are for. Same way we check things like
>> binary stars obeying GR and black holes obeying GR.
>
> Says the person who takes expansion of the universe and dark energy
> with a grain of salt, and seriously considers alternative theories...
Yep. Because we have tons of other ways of checking the same thing.
That's what makes it a theory instead of a hypothesis: You get the same
answer when you measure the value with a dozen different independent
experiments.
[1] Apparently, the same gene that causes there to be five fingers is
also related to sexual reproduction, so almost all mammals, birds, and
fish that have anything even remotely like hands and feet, wings,
flippers, fins, etc have five bones in them. Not something you'd expect,
until you look at the genes that cause that, and see they also cause
stuff necessary for sexual reproduction.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Alain <ele### [at] netscapenet> wrote:
> There have been some evolutionary experiments that have been done.
So, how many fish have they converted into cats like this?
(I hope you get the point.)
--
- Warp
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Warp wrote:
> Says the person who takes expansion of the universe and dark energy
> with a grain of salt, and seriously considers alternative theories...
Or, as an alternate way of saying this, when Sharper Image sells a
device that lets me park three cars in a two-car garage by using dark
energy, I'll suspect very strongly the cosmologists have figured it out. :-)
Now, I know very little about cosmology, and that's probably where my
skepticism comes from. But as far as I know, there's really only one
major measurement made post-hoc that supports these theories.
"Inflation" hasn't *predicted* anything, and "dark energy" hasn't
*predicted* anything. Dark matter hypothesis predicted that we'd see
colliding galaxies with the dark matter "splashing" off, as was in the
news recently.
I'd be happy to hear about other things that the hypotheses of
"inflation" or "dark energy" have predicted that were observed only
after those hypotheses were proposed. It would greatly reduce my
skepticism. :-)
> We cannot measure here and now.
We can. We can make predictions of what we'll find based on the theory,
and then when those predictions come true, it supports the theory. Such
as using genetics of different whales to figure out what the genetics of
the first cetacean would have been like, then finding the land animal
with the closest genetics, then digging around for fossils there and
finding fossils of cetaceans with feet near the shore.
Kind of like how Young Earth Creationists have a difficult time figuring
out where the oil is before they start drilling, ya know.
(To be completely clear, I'm not certain that evolution explains
*everything*. But it clearly (to me) explains the majority of what we're
seeing going on, with a large variety of correct predictions.)
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Warp wrote:
> Alain <ele### [at] netscapenet> wrote:
>> There have been some evolutionary experiments that have been done.
>
> So, how many fish have they converted into cats like this?
>
> (I hope you get the point.)
It takes a long time to convert a fish into a cat. So?
How many complete orbits of pluto have been observed? How do you know it
is really orbiting the sun?
You haven't said why you think it's unlikely to be true.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Warp nous apporta ses lumieres en ce 2008/01/03 01:50:
> John VanSickle <evi### [at] hotmailcom> wrote:
>> Oh, wait, I thought this was a real-world situation. Silly me.
>
> Given the proper circumstances (not actual trains, but something similar,
> capable of doing the feat), why wouldn't it be a real-world situation?
>
> Or are you saying that relativity doesn't work in the real world?
>
Real word trains can't go fast enough. A freight train 2000m long going twice as
fast as the fastest maglev will only have a relavistic contraction of atomic
scale, and a thermal expantion from air friction aproaching 1m.
So, your relativistic seppd solution is not viable. My critical breaking
solution is at least tryable. Each wagon coupling can contract almost 30cm,
multiply that by the number of wagons in a typical freight train, and the train
can contract a few meters.
--
Alain
-------------------------------------------------
Methodist: It's not so bad if shit happens, as long as you serve grape juice
with it.
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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> > Alain <ele### [at] netscapenet> wrote:
> >> There have been some evolutionary experiments that have been done.
> >
> > So, how many fish have they converted into cats like this?
> >
> > (I hope you get the point.)
> It takes a long time to convert a fish into a cat. So?
> How many complete orbits of pluto have been observed? How do you know it
> is really orbiting the sun?
Yes, both things are comparable in complexity.
--
- Warp
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Darren New <dne### [at] sanrrcom> wrote:
> I'd be happy to hear about other things that the hypotheses of
> "inflation" or "dark energy" have predicted that were observed only
> after those hypotheses were proposed. It would greatly reduce my
> skepticism. :-)
You are welcome to propose a better theory. (How come this sounds
familiar?)
--
- Warp
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Alain <ele### [at] netscapenet> wrote:
> Real word trains can't go fast enough.
Yes, and machines will never fly.
--
- Warp
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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> I'd be happy to hear about other things that the hypotheses of
>> "inflation" or "dark energy" have predicted that were observed only
>> after those hypotheses were proposed. It would greatly reduce my
>> skepticism. :-)
>
> You are welcome to propose a better theory. (How come this sounds
> familiar?)
I have no better theory. However, I have no evidence at all that the
current theory is "right". I'm sure someone probably has some evidence,
but that's why I asked for the evidence, you see. Maybe there's a whole
bunch of evidence pointing to dark energy as a real thing out there, and
I just haven't heard about it. Given how wide-spread the "dark matter"
evidence was all over, I kind of doubt it.
The difference, again, is that when evidence is presented that a theory
is correct, I can actually change my mind. :-)
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> Warp wrote:
>>> Alain <ele### [at] netscapenet> wrote:
>>>> There have been some evolutionary experiments that have been done.
>>> So, how many fish have they converted into cats like this?
>>>
>>> (I hope you get the point.)
>
>> It takes a long time to convert a fish into a cat. So?
>
>> How many complete orbits of pluto have been observed? How do you know it
>> is really orbiting the sun?
>
> Yes, both things are comparable in complexity.
No, of course not. But you haven't expressed why you think creating a
new species over the course of a few weeks or a few years couldn't
easily lead to creating a cat out of a fish over the course of a few
million. All the mechanisms to make it happen are understood, and
technology makes use of the same mechanisms both in living and
non-living environments.
What would be the boundary for you? Do you believe that drug-resistant
TB is evolved from earlier TB? Do you believe that seedless grapes
evolved from grapes with seeds? Do you believe that dogs evolved from
wolves (or whatever the appropriate order is)? Just curious.
I just don't understand how you can be presented with boatloads of
evidence for a theory, have no conflicting evidence, have no alternate
theory to propose that explains any of the evidence, and still say "I
don't think it could be right." It just sounds a bit crazy to me.
But that's OK.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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And lo on Wed, 02 Jan 2008 17:16:20 -0000, Darren New <dne### [at] sanrrcom>
did spake, saying:
> Darren New wrote:
>> But the conductor of the eastbound train will see the westbound train
>> get onto the tracks later than he does, and vice versa.
>
> Actually, I meant to say "may see" there. And it looks like based on
> that wikipedia article that the conductor will actually see the other
> train get to its junction *before* he gets to his own. Very strange.
Though won't the double track also seem foreshortened?
To quote from somewhere - a conductor stands on the platform of the train
station and sees that the railline has collapsed leaving a large hole. The
train coming towards him is travelling at near-light speed and the
shortening effect means that from the conductor's POV the train is short
enough to fit neatly into the hole, except he can see that it's travelling
so fast it'll just sail straight over the gap without falling far enough
to get stuck. From the train's POV the hole is shortened to a tiny gap so
the driver expects to experience just a small jolt as he goes over it. So
both points of view match the expectations of both.
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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Darren New nous apporta ses lumieres en ce 2008/01/03 21:10:
> Warp wrote:
>> Darren New <dne### [at] sanrrcom> wrote:
>>> Warp wrote:
>>>> Alain <ele### [at] netscapenet> wrote:
>>>>> There have been some evolutionary experiments that have been done.
>>>> So, how many fish have they converted into cats like this?
>>>>
>>>> (I hope you get the point.)
>>
>>> It takes a long time to convert a fish into a cat. So?
>>
>>> How many complete orbits of pluto have been observed? How do you know
>>> it is really orbiting the sun?
>>
>> Yes, both things are comparable in complexity.
>
> No, of course not. But you haven't expressed why you think creating a
> new species over the course of a few weeks or a few years couldn't
> easily lead to creating a cat out of a fish over the course of a few
> million. All the mechanisms to make it happen are understood, and
> technology makes use of the same mechanisms both in living and
> non-living environments.
>
> What would be the boundary for you? Do you believe that drug-resistant
> TB is evolved from earlier TB? Do you believe that seedless grapes
> evolved from grapes with seeds? Do you believe that dogs evolved from
> wolves (or whatever the appropriate order is)? Just curious.
>
> I just don't understand how you can be presented with boatloads of
> evidence for a theory, have no conflicting evidence, have no alternate
> theory to propose that explains any of the evidence, and still say "I
> don't think it could be right." It just sounds a bit crazy to me.
>
> But that's OK.
>
They actualy made dogs out of foxes. Over just a few generation, taking only the
more dociles and crossbreading them. The foxes went from redish fur to brown and
black fur, stoped yaping to start barking.
The goal was to ease the farm raising of foxes for the furs.
--
Alain
-------------------------------------------------
You know you've been raytracing too long when your personal correspondence to
friends starts out with #Dear Linda =
Ken Tyler
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Phil Cook wrote:
> Though won't the double track also seem foreshortened?
Yes, but the oncoming train will seem *more* foreshortened.
> travelling so fast it'll just sail straight over the gap without falling
> far enough to get stuck.
Not ... exactly. The problem isn't that he doesn't fall far enough. The
problem is that the bottom of the train starts falling before the top
does, kind of.
And in that case, there are only two speeds involved (the track and the
train), rather than the three in Warp's original problem.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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Alain wrote:
> They actualy made dogs out of foxes. Over just a few generation, taking
> only the more dociles and crossbreading them. The foxes went from redish
> fur to brown and black fur, stoped yaping to start barking.
> The goal was to ease the farm raising of foxes for the furs.
I saw that. They also got floppy ears and curly tails. :-)
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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"Warp" <war### [at] tagpovrayorg> wrote in message
news:477abc37@news.povray.org...
> Xavier Manget <NOS### [at] freefr> wrote:
>> If the trains' speeds are close enough to the speed of light,
>> because of
>> relativistic length contraction (and with correct timing) the
>> trains will
>> have enough length to pass each other on the double track?...
>
>> Did I get it? :-p
>
> Yes.
>
> (Had you heard of the thought experiment, or did you figure it
> out on
> your own?)
>
> --
> - Warp
This could only be true if the trains and the track are uncoupled.
They are not, so any contraction of trains will apply equally to
the
track. Same problem, different scale for an outside observer.
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pan <pan### [at] syixcom> wrote:
> This could only be true if the trains and the track are uncoupled.
> They are not, so any contraction of trains will apply equally to
> the
> track.
Nope. The trains are moving at a different speed than the track and
thus the trains compress more.
--
- Warp
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Warp wrote:
> Nope. The trains are moving at a different speed than the track and
> thus the trains compress more.
More specifically, from the POV of one train, the other train is moving
faster than the track is.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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And lo on Fri, 04 Jan 2008 19:19:43 -0000, Darren New <dne### [at] sanrrcom>
did spake, saying:
> Phil Cook wrote:
>> Though won't the double track also seem foreshortened?
>
> Yes, but the oncoming train will seem *more* foreshortened.
>
>> travelling so fast it'll just sail straight over the gap without
>> falling far enough to get stuck.
>
> Not ... exactly. The problem isn't that he doesn't fall far enough. The
> problem is that the bottom of the train starts falling before the top
> does, kind of.
>
> And in that case, there are only two speeds involved (the track and the
> train), rather than the three in Warp's original problem.
From an outside observer's pov both trains are shorter then the double
track so should pass without problem; I was trying to reconcile it with
the traindrivers' view. The oncoming train is shorter, but so is the
double track; so they should still collide?
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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Phil Cook <phi### [at] nospamrocainfreeservecouk> wrote:
> From an outside observer's pov both trains are shorter then the double
> track so should pass without problem; I was trying to reconcile it with
> the traindrivers' view. The oncoming train is shorter, but so is the
> double track; so they should still collide?
From the POV of one of the trains the other train is shortened *more*
than the track.
--
- Warp
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And lo on Mon, 07 Jan 2008 11:44:23 -0000, Warp <war### [at] tagpovrayorg> did
spake, saying:
> Phil Cook <phi### [at] nospamrocainfreeservecouk> wrote:
>> From an outside observer's pov both trains are shorter then the double
>> track so should pass without problem; I was trying to reconcile it with
>> the traindrivers' view. The oncoming train is shorter, but so is the
>> double track; so they should still collide?
>
> From the POV of one of the trains the other train is shortened *more*
> than the track.
If they were travelling at the same speed I'd have thought that the
shortening of both track and train would be proportional from the view of
the other train?
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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Phil Cook <phi### [at] nospamrocainfreeservecouk> wrote:
> If they were travelling at the same speed I'd have thought that the
> shortening of both track and train would be proportional from the view of
> the other train?
The trains travel at the same speed (in relation to the track) but in
opposite directions. Thus from the POV of one of the trains the other
train is approaching faster than the double track.
--
- Warp
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And lo on Mon, 07 Jan 2008 12:38:14 -0000, Warp <war### [at] tagpovrayorg> did
spake, saying:
> Phil Cook <phi### [at] nospamrocainfreeservecouk> wrote:
>> If they were travelling at the same speed I'd have thought that the
>> shortening of both track and train would be proportional from the view
>> of
>> the other train?
>
> The trains travel at the same speed (in relation to the track) but in
> opposite directions. Thus from the POV of one of the trains the other
> train is approaching faster than the double track.
Okay I'm the driver of one train and you're the driver of the other.
I see that your train is shorter then the double section of track and that
you're travelling faster then I am, therefore you hit the double section
before I do. But my train is still the same length as the double track (or
longer), so although I can clear the section without hitting the end of
your train (because you're shorter) I would expect you to hit the end of
my train (because you're faster).
I mean I can it understand how it works from Darren's perspective sitting
by the track, just not from the drivers.
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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And lo on Mon, 07 Jan 2008 15:01:51 -0000, Phil Cook
<phi### [at] nospamrocainfreeservecouk> did spake, saying:
> And lo on Mon, 07 Jan 2008 12:38:14 -0000, Warp <war### [at] tagpovrayorg>
> did spake, saying:
>
>> Phil Cook <phi### [at] nospamrocainfreeservecouk> wrote:
>>> If they were travelling at the same speed I'd have thought that the
>>> shortening of both track and train would be proportional from the view
>>> of
>>> the other train?
>>
>> The trains travel at the same speed (in relation to the track) but in
>> opposite directions. Thus from the POV of one of the trains the other
>> train is approaching faster than the double track.
>
> Okay I'm the driver of one train and you're the driver of the other.
>
> I see that your train is shorter then the double section of track and
> that you're travelling faster then I am, therefore you hit the double
> section before I do. But my train is still the same length as the double
> track (or longer), so although I can clear the section without hitting
> the end of your train (because you're shorter) I would expect you to hit
> the end of my train (because you're faster).
>
> I mean I can it understand how it works from Darren's perspective
> sitting by the track, just not from the drivers.
Ah got it I think. Although both trains hit the double track at the same
time from my train you haven't reached it yet, so if I see you as 1/4 of
the length of the section I can be halfway along the double track before
you've even got on it. So I'll reach my end when you're clear and you
won't reach your end (despite being faster) until I've cleared your end
(my start).
Ouch yeah that works, we each perceive the other as reaching the double
section after ourselves.
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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Phil Cook wrote:
> And lo on Fri, 04 Jan 2008 19:19:43 -0000, Darren New <dne### [at] sanrrcom>
> did spake, saying:
>
>> Phil Cook wrote:
>>> Though won't the double track also seem foreshortened?
>>
>> Yes, but the oncoming train will seem *more* foreshortened.
>>
>>> travelling so fast it'll just sail straight over the gap without
>>> falling far enough to get stuck.
>>
>> Not ... exactly. The problem isn't that he doesn't fall far enough.
>> The problem is that the bottom of the train starts falling before the
>> top does, kind of.
>>
>> And in that case, there are only two speeds involved (the track and
>> the train), rather than the three in Warp's original problem.
>
> From an outside observer's pov both trains are shorter then the double
> track so should pass without problem; I was trying to reconcile it with
> the traindrivers' view. The oncoming train is shorter, but so is the
> double track; so they should still collide?
No, because the oncoming westbound train is coming at the eastbound
train faster than the tracks are coming at the eastbound train, so the
westbound train appears to be smaller than the siding as seen from the
eastbound train.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
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"Warp" <war### [at] tagpovrayorg> wrote in message
news:477fd1d1@news.povray.org...
> pan <pan### [at] syixcom> wrote:
>> This could only be true if the trains and the track are
>> uncoupled.
>> They are not, so any contraction of trains will apply equally to
>> the
>> track.
>
> Nope. The trains are moving at a different speed than the track
> and
> thus the trains compress more.
>
> --
> - Warp
Train wheels gripping track exponentially gets looser
the greater the speed of the train. At c or near c the
track will have to move almost the entire speed of the
train; else the instability will overwhelm your system.
ergo: the track and train muts be coupled, else you
would be asking about trains and tracks on separate
unique vectors. (Unpredictable vectors btw)
unless of course your train wheels and track rails are
made of unobtanium held together in the grip of
stick-but-slick-enough-to-let-the-wheels-move goop.
Think dentures under a lot of strain.
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pan <pan### [at] syixcom> wrote:
> Train wheels gripping track exponentially gets looser
> the greater the speed of the train. At c or near c the
> track will have to move almost the entire speed of the
> train; else the instability will overwhelm your system.
> ergo: the track and train muts be coupled, else you
> would be asking about trains and tracks on separate
> unique vectors. (Unpredictable vectors btw)
> unless of course your train wheels and track rails are
> made of unobtanium held together in the grip of
> stick-but-slick-enough-to-let-the-wheels-move goop.
> Think dentures under a lot of strain.
I don't even understand what you are trying to say.
But if the contact with the train and the track bothers you, then
assume maglev.
--
- Warp
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> But if the contact with the train and the track bothers you, then
> assume maglev.
What about when the trains have to turn when the track splits? That is the
bit that bothers me most at those speeds...
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scott <sco### [at] laptopcom> wrote:
> What about when the trains have to turn when the track splits? That is the
> bit that bothers me most at those speeds...
The trains and the double track segment can be really long, meaning that
the turn can be very subtle.
--
- Warp
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And lo on Mon, 07 Jan 2008 17:32:22 -0000, Darren New <dne### [at] sanrrcom>
did spake, saying:
> Phil Cook wrote:
>> And lo on Fri, 04 Jan 2008 19:19:43 -0000, Darren New <dne### [at] sanrrcom>
>> did spake, saying:
>>
>>> Phil Cook wrote:
>>>> Though won't the double track also seem foreshortened?
>>>
>>> Yes, but the oncoming train will seem *more* foreshortened.
>>>
>>>> travelling so fast it'll just sail straight over the gap without
>>>> falling far enough to get stuck.
>>>
>>> Not ... exactly. The problem isn't that he doesn't fall far enough.
>>> The problem is that the bottom of the train starts falling before the
>>> top does, kind of.
>>>
>>> And in that case, there are only two speeds involved (the track and
>>> the train), rather than the three in Warp's original problem.
>> From an outside observer's pov both trains are shorter then the
>> double track so should pass without problem; I was trying to reconcile
>> it with the traindrivers' view. The oncoming train is shorter, but so
>> is the double track; so they should still collide?
>
> No, because the oncoming westbound train is coming at the eastbound
> train faster than the tracks are coming at the eastbound train, so the
> westbound train appears to be smaller than the siding as seen from the
> eastbound train.
Check my later comments on how this could still mean they collide; I think
I've got it now anyway thanks.
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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