
Discover the Ladder Paradox, relativity's greatest thought experiment - jonbaer
http://io9.com/discover-the-ladder-paradox-relativitys-greatest-thou-1219502372
======
panic
A picture would be worth a thousand words here. An interactive illustration
would be worth a million. Instead, the article has two totally irrelevant
images and a bunch of hard-to-follow prose.

Why, in 2013, are we still forcing people to construct images in their head
based on words instead of showing them the full picture on their computer?

~~~
glurgh
It's essentially linkbait spam. Just google 'ladder paradox' or 'barn-pole
paradox' for a zillion detailed, often illustrated explanations. "Relativity's
greatest thought experiment" itself is a tip off. Says who? Einstein and
popularizers like, say, Carl Sagan were fond of

"[...] a paradox upon which I had already hit at the age of sixteen: If I
pursue a beam of light with the velocity c (velocity of light in a vacuum), I
should observe such a beam of light as an electromagnetic field at rest though
spatially oscillating. There seems to be no such thing, however, neither on
the basis of experience nor according to Maxwell's equations. [...]"

You can also make a reasonable argument that this is relativity's greatest
thought experiment:

[http://physics.syr.edu/courses/modules/LIGHTCONE/galileo.htm...](http://physics.syr.edu/courses/modules/LIGHTCONE/galileo.html)

Edit:

In an internet long past, when it was small enough to have such a thing as a
physics FAQ, this was among them.

[http://www.faqs.org/faqs/physics-
faq/part4/](http://www.faqs.org/faqs/physics-faq/part4/)

The first chapter of the referenced Taylor & Wheeler 'Spacetime Physics' can
be found here:

[http://www.eftaylor.com/download.html](http://www.eftaylor.com/download.html)

------
mikegagnon
> "Although we can think of reality as objective, there are some special cases
> that prove it's nothing of the kind."

This paradox does not say anything about the objectiveness of reality. Rather
it just points out an interesting scenario in which individual perceptions of
objective reality won't match up.

~~~
Retric
Not quite, assuming both observers had an accurate model of physics physics
they would construct identical models of what happened. The difference is
simply which coordinate system was used. So, they could for example predict
what an observer on the other object saw.

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dsego
I prefer the train going through a tunnel version. Here it is better
explained:

Relativity Paradox - Sixty Symbols
[http://www.youtube.com/watch?v=kGsbBw1I0Rg](http://www.youtube.com/watch?v=kGsbBw1I0Rg)

------
cperciva
I don't understand, where's the paradox?

~~~
RazerM
From the reference frame of the garage, the ladder is moving with a
relativistic velocity and therefore experiences length contraction. From the
equally valid reference frame of the ladder, it is the garage that is moving
with a relativistic velocity, making it even smaller (so the ladder wouldn't
fit).

------
raldi
To reduce this article to one sentence: The answer to the question "Which
happened first, Event A or Event B?" depends on where you are.

~~~
gus_massa
It doesn't depend on where you are. The "explanation" at the end of the
article is misleading. If you are sited next to a door you will "see" that
your door closes before the other. But as you know the distance between the
doors you can make the correction and calculate the exact time when the other
door closed. After the correction you will realize that both doors closed at
the same time in spite you don't "see" them closing at the same time.

You will have the same effect sitting at the other door. If you are sitting in
between you must apply the corrections to both doors, and then you will
realize that they really closed at the same time. The only point were you
"see" at the same time that both doors close is in the middle, and obviously
after the corrections you will realize that they really closed at the same
time.

The important thing is your velocity. Let's suppose that you are traveling
(very) fast with the ladder, holding it at the middle point. You will first
"see" that the back door closes (and reopen) before the top of the ladder get
to that point. Then you will see that the front door closes (and reopen) after
the bottom of the ladder passed that point. But you still have to make the
corrections because both doors are far away. Even after the corrections the
back door close and reopens _before_ the front door close and reopens.

If you hold the ladder form one extreme you will "see" essentially the same
things, and after the corrections you will be sure that never were both doors
closed at the simultaneously. An important detail is that the difference of
time between the reopening of the back door and the closing of the front door
doesn't depend on where are you holding the ladder. After the corrections you
will get the same time interval.

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ktran03
That was unenlightening.

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avdd_
schrodinger's ladder?

------
aroberge
Basic, well-known undergraduate first (or perhaps second) year physics topic
making the front page of HN ?? Is this turning into a forum for high school
students?

~~~
RazerM
Not everyone studies this level of physics at all, and it certainly "gratifies
one's intellectual curiosity".

~~~
voiceoftruth01
Football "gratifies my intellectual curiosity". Shall I start spamming hn with
football threads then? Retard.

~~~
RazerM
From the HN Guidelines [1]:

> On-Topic: Anything that good hackers would find interesting. That includes
> more than hacking and startups. If you had to reduce it to a sentence, the
> answer might be: anything that gratifies one's intellectual curiosity.

> Off-Topic: Most stories about politics, or crime, or _sports_ , unless
> they're evidence of some interesting new phenomenon. Videos of pratfalls or
> disasters, or cute animal pictures. If they'd cover it on TV news, it's
> probably off-topic.

[1]:
[http://ycombinator.com/newsguidelines.html](http://ycombinator.com/newsguidelines.html)

