
Ask HN: Building a Computer in Jesus's Time - BracketMaster
I keep thinking about if I suddenly went back in time, how hard would it be to make a computer?<p>Could I at least make a vacuum tube?
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qohen
Perhaps not exactly what you have in mind, but there is the Antikythera
mechanism [0][1], the first known analog computer, dating back to about
100-200 BCE which exhibits gear-work that one doesn't see for another 1500
years or so. The device calculates the phases of the moon and the motion of
the known planets and more for any date over a 76 year cycle. It takes into
account the retrograde motion of Mars, can calculate the dates of eclipses,
etc. There are videos on YouTube showing how it is supposed to have worked,
e.g. [2].

[0]
[https://en.wikipedia.org/wiki/Antikythera_mechanism](https://en.wikipedia.org/wiki/Antikythera_mechanism)

[1] [https://www.age-of-the-
sage.org/archaeology/antikythera_mech...](https://www.age-of-the-
sage.org/archaeology/antikythera_mechanism.html)

[2]
[https://www.youtube.com/watch?v=ML4tw_UzqZE](https://www.youtube.com/watch?v=ML4tw_UzqZE)

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tdeck
Given limited technology and the desire for something electric and
programmable I think your best bet would be a relay computer. Konrad Zuse
built the Z1 entirely out of hand-cut sheet metal strips in his parents'
living room:

[https://en.wikipedia.org/wiki/Z1_%28computer%29?wprov=sfla1](https://en.wikipedia.org/wiki/Z1_%28computer%29?wprov=sfla1)

That said, you would need lots of flexible ferrous metal and a source of
electricity, probably large voltaic piles. And you would need to find a way to
produce and insulate large amounts of wire.

~~~
java-man
one could build logic gates with ropes (and elephants).

[0]
[https://www.jstor.org/stable/24989059?seq=1](https://www.jstor.org/stable/24989059?seq=1)

[1]
[https://www.i-programmer.info/news/112-theory/7370-pulleys-a...](https://www.i-programmer.info/news/112-theory/7370-pulleys-
as-logic-gates.html)

------
AnimalMuppet
Well... Wikipedia, in the article on glassblowing, says that the earliest
example came from Jerusalem, dated from 37 to 4 BC.

Making the metal parts was well within their power. At least the shapes,
though maybe not the alloys that we would use. Getting that shape inside the
blown glass might be harder, given the tech of the day.

Getting a vacuum in it might be the hardest step. In fact, I don't know that
it was possible at all, given the tech they had available. The first vacuum
pump was in 1654.

------
java-man
If you suddenly went back in time, you would be floating in vaccum of space
millions of miles away from Earth, so the answer is probably no.

------
dekhn
There are several appropriate times in history when the necessary details were
aligned for rapid (<200 year) progress from basic manual labor industry to
advanced manufacturing. I assume that a mechanical pre-computer like Babbage's
difference engine, rather than a fully reprogrammable electrical system, is
acceptable.

Certainly within the history of China, India, and various African, Greek, and
Middle Eastern cultures, complex mechanical devices with sequencers and even
primitive logic gates were being implemented. See, for example
[https://en.wikipedia.org/wiki/Ismail_al-
Jazari](https://en.wikipedia.org/wiki/Ismail_al-Jazari) as well as
[https://en.wikipedia.org/wiki/Tang_dynasty#Alchemy,_gas_cyli...](https://en.wikipedia.org/wiki/Tang_dynasty#Alchemy,_gas_cylinders,_and_air_conditioning)
as examples where societies combined the necessary wealth, stability,
education, social and religious culture to build very impressive mechanical
devices.

I'm going to assume also that you have The Knowledge
([https://www.amazon.com/gp/product/B00DMCV5YS](https://www.amazon.com/gp/product/B00DMCV5YS))
all the way up to basic electronics.

At that point you would have everything required to gather people and money
and time to build a relay- or vacuum-tube based computer. I recommend reading
the early sections of The Idea Factory [https://www.amazon.com/Idea-Factory-
Great-American-Innovatio...](https://www.amazon.com/Idea-Factory-Great-
American-Innovation/dp/0143122797) describing what the early Bell Labs was
like. Many modern innovations came from itinerant scientists who interned at
Bell Labs, learned to make vacuum tubes by hand (IE, blowing air precisely
into molten glass, and sealing the various electronics in place) and then left
to found companies that utilized tubes (for example, Beckman went through this
process and used the acquired knowledge to build a vacuum-tube based amplifier
which was critical to the modern pH meter).

Now, a few challenges. Since you're just dropping back into a society that
hasn't undergone an industrial revolution, you don't have a bunch of useful
cross-supporting things like a healthy industry that makes high quality alloy
steel for you, or optics companies which design and sell sophisticated lens
assemblies for high quality telescopes to debug your work, or electronics
companies pumping out millions of standard resistors with tight variances,
etc. Without those, many steps that would be trivial would instead take
extended time. Also, the absence of a statistical quality culture (see Deming)
and the fact that most components will be built by hand by artisans means that
your computer will not be very reliable (producing incorrect results, or
breaking often).

On top of that, you'll probably face skepticism because your early computers
won't be able to do anything useful compared to skilled humans. You would
probably do best by finding a local military leader and convincing them you
could help with ballistics calculations...

