
The Last Question - Isaac Asimov - lisperforlife
http://www.multivax.com/last_question.html
======
ars
Previous submissions:

<http://news.ycombinator.com/item?id=140283>

<http://news.ycombinator.com/item?id=595419>

<http://news.ycombinator.com/item?id=1078831>

<http://news.ycombinator.com/item?id=1485286>

<http://news.ycombinator.com/item?id=1290590>

<http://news.ycombinator.com/item?id=2467703>

Some have more comments than others.

~~~
mrleinad
Yeah, can't imagine how this submission made it to the front page of HN.

~~~
unimpressive
Things have a tendency to resurface. I personally had not read it before.
Though since the HN search is so good (Probably in the top ten I've seen so
far for content search on a site.) theres not as much of an excuse for
resubmission.

~~~
drostie
An implementation of exponential decay could quite possibly solve this
problem, but it might mean that they'd have to dramatically rethink the "new"
page.

Exponential decay is important because it is, as they say in statistics,
"memoryless": it has a simple geometric property that adding a new point today
has the exact same effect as adding a new point on the first day. It can
therefore be implemented as follows: when you add points to a link, you add
them not just to the total points, but also to some accumulator which I will
call Hotness. This number is a double; we increment by 1 when someone adds a
point.

Every half-hour, some independent process working over still-Hot threads
multiplies their Hotness by 0.97153. This gives a half-life of about 12 hours:
your rating has hotness 0.5 after half a day, 0.25 after a whole day, and so
on. We could tune that if we wanted finer granularity. When something gets
below 0.001 Hot we can probably just reset it to 0 Hot abruptly so that we
don't check it anymore. (Because doubles will try to go to -infinity if you
use them multiplicatively in this way, and if you get to, say, 1000 points
this will still mean that we can stop paying attention to you in, say, 10
days.)

Suddenly, adding points to a dead article is the exact same as sponsoring a
new article. So we store articles under their URLs as keys, and if you
resubmit an existing news story you merely bump it up to 1 Hot.

The "new" page would be very peculiar in this system, though. It might work by
listing only those 1 Hot posts which were 0 Hot previously, I don't know.

As for a major con to this approach, I think HN uses polynomial decay rather
than exponential decay because exponential decay somehow didn't feel like it
had the right "shape" to it or so. This is probably because they didn't
implement it in the "memoryless" configuration, though, where each point has
value 1 from the moment it's added, and decays slowly.

~~~
abentspoon
Better still, increment hotness by 2^(dt/λ) where dt is the time since the
site was launched (epoch), and λ the halflife of an upvote. No worker process
needed.

Doubles will go to infinity after a few years, but you can either reset the
epoch at that time, or store the significand and the exponent seperately.

~~~
drostie
I agree partways with what you're saying; the normal fears of losing precision
in your floats don't really apply because you're always adding the smallest
numbers first. On the other hand, your worker process is still in my view a
worker process, processing every article by multiplying its hotness by
1.77e-220, and resetting t0. I mean, I believe it's a single SQL query, so it
probably shouldn't impact site performance too much even for databases as
large as Hacker News, so I'm not so worried about the sudden inconsistency
while the worker is doing its thing -- but it's still a dedicated thing-on-
the-side which has to be scheduled e.g. via cron job, and which you'd have to
audit every once in a while to make sure that it did its job successfully and
didn't accidentally get pushed out of sync by, say, server reboots.

------
Jun8
Some comments:

1) I've heard many (non-physicist) people argue/think that the 2nd Law of
Thermodynamics is a law in the sense that, say, General Relativity or
Conservation of Energy is a law. That is not true. As explained here
([http://physics.stackexchange.com/questions/4201/why-does-
the...](http://physics.stackexchange.com/questions/4201/why-does-the-low-
entropy-at-the-big-bang-require-an-explanation-cosmological-a)) the basic laws
of physics are time-symmetric, i.e. there's no currently known _fundamental_
reason that entropy behaves the way it does.

2) I've read this story 20+ times, yet each time it gets me. I think the force
of the story comes not from the scientific predictions but from the poignant
depiction of humanity's futile fight against oblivion. Aren't all monuments
erected for this purpose? The fact that the story is very light on the tech
details paradoxically increases its punch.

3) The described technology is a curious mix of far-sight and ridiculous
backwardness: In describing harnessing the power of the Sun, Asimov may have
had in mind something like a Dyson sphere, which Dyson described in 1960.
However, the technicians still use a teletype to communicate with Multivac in
2061!

4) One thing that I think Asimov got wrong fundamentally is that researching
the "final question" should have taken all of Multivac's CPU capacity. It's
stupendous that Multivac just runs _that_ question on a separate thread while
doing everything else. _The Hitchiker's Guide_ gets this right: when Arthur
asks a very powerful AI (the Nutrimatic Drinks Dispenser) to make tea it
totally paralyzes the machine.

5) I've never been able to find a good interpretation of Cosmic AC's response
"NO PROBLEM IS INSOLUBLE IN ALL CONCEIVABLE CIRCUMSTANCES."

~~~
archangel_one
The mix of far-sight and backwardness you describe in (3) is common to a lot
of sci-fi. I remember one book of Clarke's that describes a journalist taking
a trip to the colony on Mars, and to write his articles he takes a portable
typewriter with him. There are a lot of anachronisms in Asimov's early
Foundation novels as well, such as many characters smoking, a total lack of
computers and everything still being done by humans - taxi drivers, customs
officers stamping passports, etc. I guess it's a pretty hard thing to see what
parts of society are going to be replaced, especially given some of the
disruptive technologies like computers that have popped up mostly after these
books were written.

Couldn't (4) just represent a fairly good design for Multivac so asking it one
hard question doesn't lock it up for everyone else?

~~~
krelian
I actually enjoy this mix of old and new in sci-fi, from an artistic
viewpoint, that is. It gives it this little flavor that is a mix between very
high technological advancement and simple nostalgia (obviously not intentional
by the author, just a side effect of me reading this story in 2012). When I
try to imagine a cool fictional cyberpunk future, I find it much more
satisfying to picture hackers hacking away at the keyboard in front a screen
filled with green text over black background than the more plausible shiny
white touchscreen.

I prefer my space exploration to be done on a Nostromo than a Enterprise.

------
abentspoon
Another favorite of mine: Learning to be Me - Greg Egan

<http://qwerjk.com/force-feed#learning-to-be-me>

~~~
ableal
Also, John Varley's story Overdrawn at the Memory Bank

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iandanforth
Why do humans have to re-submit these? If a post is 1. Timeless and 2. Popular
shouldn't this be automated?

Surely this post adds to the experience of some as do many others like it. The
first step in this trend would be a Hacker New reading list composed of posts
that fit this profile.

Secondarily you could have a way to inject each of the posts on that list into
each users front page based on if they had seen it before (followed link
checking or HN logs). If I'm new to HN perhaps my front page would have these
scattered throughout.

Next you could use them as content on slow news days in combination with the
per user information above.

I, for one, would love it if my local movie theatre re-ran Star Wars during
slow months, and I wouldn't mind being (re)exposed to classic posts on Sunday
afternoons :)

~~~
kaybe
Arguments have been made that it's better for all of us to see the same
frontpage. I can't find them right now though. But I agree on the 'classics'
page.

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PhilipDaineko
"Man, mentally, was one. He consisted of a trillion, trillion, trillion
ageless bodies, each in its place...minds of all the bodies freely melted one
into the other" Seems it's going to be true. When you google for something
it's already some kind of thought of Man. For now connections between
individuals are very slow, but it will be solved soon. I'll have a chip in my
head which will allow me to share my thoughts immediately with anybody.

~~~
heed
I find this idea sad. I like my individuality.

------
thret
Twenty-odd years ago, a friend and I were discussing entropy with our physics
teacher and my friend related this story. He couldn't remember where he had
read it. I have wanted to read it ever since.

However many times classics are resubmitted, they will still find new and
appreciative readers. Thank you lisperforlife & HN.

------
javajosh
We need to focus on inhabiting just one other world, first. The longer-term
problem of universal heat death will work itself out.

~~~
jacquesm
We need to focus on managing the one that we've got, first.

And so far we're doing a piss-poor job of it.

~~~
javajosh
I'd argue we need to do both, but that getting off-planet is actually the
bigger priority: even if we run our planets poorly, we'll be safe from
complete extinction, which gives us time to optimize in the long run.

~~~
jacquesm
No, you have that backwards.

Taking care of what we have right now is the bigger priority because failing
that we never will get off the planet anyway.

Getting off the planet requires a larger degree of international cooperation
and funding than stewarding our own planet does. If we can't manage the one we
certainly won't be able to manage the other. Also, it is something that we
actually can do, if we set our minds to it. Whether or not we can actually get
off the planet with meaningful numbers of people to a place that is no longer
tied to the earth in some critical way remains to be seen.

~~~
dandrews
More international cooperation? International _competition_ got us into space
to begin with.

------
LiveTheDream
How can entropy be reversed? [http://www.multivax.com/cgi-
bin/ask_multivax.pl?query=How+ca...](http://www.multivax.com/cgi-
bin/ask_multivax.pl?query=How+can+entropy+be+reversed%3F&ask=Ask+MultiVAX)

------
derefr
> Can entropy ever be reversed?

I might not be understanding the science correctly, but due to the specific
phrasing of the question, would "Sure--here's a schematic for an LED that
converts waste heat back into photons[1]" be an acceptable answer?

[1] <http://www.physorg.com/news/2012-03-efficiency.html> (Previously
discussed on HN)

~~~
nullc
It uses energy to do so— just like a heat pump can heat your home with greater
output than electrical input, but not no electrical input.

The more exciting detail is that computation itself doesn't increase entropy,
at least not if reversible computing is use. Only errors or, rather, their
correction do... So things may be more rosy than you might guess:
<http://arxiv.org/abs/quant-ph/9908043>

