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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