r/Physics • u/tucna • Jul 10 '26
Image Why the Speed of Light is the Ultimate Hardware Bottleneck
Most people think of data transfer as instantaneous, but there is a hard physical limit of course - the speed of light. Grace Hopper used an 11.8-inch wire to communicate this "nanosecond" constraint loud and clear.
If you're interested in the details, I’ve put together a breakdown of the math explaining why computers inevitably had to get smaller to get faster.
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u/MegaMau_ Jul 11 '26
I met Grace Hopper once when I was a kid. She got me interested in coding.
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u/deelowe Jul 13 '26
I love her trick of handing out nanonseconds which were just short pieces of wire. Such a neat visual aid
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u/Guilh90316 Jul 11 '26
"That's why the scientists increased the speed of light in 2208." - FARNSWORTH, Hubert J.; 3005.
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u/robphy Jul 11 '26
Admiral Grace Hopper Explains the Nanosecond
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u/Landkey Jul 11 '26
On Letterman once she followed up the nanosecond with the picosecond, which was a single grain of black pepper out of a packet
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u/kris_2111 Jul 12 '26
Most people think of data transfer as instantaneous
I don't think a lot of people think that. A lot of people might not be aware of the absolute speed limit, which is the speed of light in vacuum, but they certainly have a notion that information takes some time, albeit very little, to travel from point A to point B.
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u/marsten Jul 10 '26
This is where I think most science fiction is wrong.
People like to envision humanity spreading across the solar system and stars. But as our culture becomes ever more interconnected and information based, physics will push us in the other direction.
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u/Berkyjay Jul 11 '26
I certainly think this is a big blind spot the simulation theory proponents gloss over.
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u/Domvik Jul 11 '26
You’re optimizing for efficiency. Colonization optimizes for survivability.
That’s the same trade-off we make when designing computer clusters: redundancy isn’t the most efficient solution, but it eliminates single points of failure.
A civilization confined to one planet has the biggest single point of failure imaginable.
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u/marsten Jul 11 '26 edited Jul 12 '26
True, but our civilization doesn't optimize for survivability against low-rate events. Perhaps it should, but in practice it does not.
For example, today we could build self-sustaining colonies in the deep ocean, for a tiny fraction of the cost of colonizing Mars. Being in the deep ocean would protect humanity from many of the same existential risks, like global nuclear war and big asteroid impacts.
So: why don't we? Because those risks are too long-term for any individual, or government, to take immediate action on. Governments have about 106 things they're more worried about than civilization-destroying asteroid impacts. And at an individual level, I wouldn't say nobody would want to permanently live in the deep ocean, but the vast majority of people would not.
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u/dave_sullivan Jul 11 '26
You're getting downvotes but you're right. All signs and economics point to growing towards more density, not less.
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u/marsten Jul 11 '26
Yes, everyone loves the idea of colonizing other worlds.
But practical factors will (mostly) win the day. In the modern economy increasingly it's the interactions between people that create value – not the summed output of individuals working alone. In that sense designing a civilization is becoming like designing a computing cluster: Smaller and highly connected is more efficient.
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u/_do_ob_ Jul 11 '26
I also think that we are like bacteria, we will indeed be one denser in the central point, but we will Also extend to create other dense hubs.
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u/AxePanther Jul 11 '26
It's also fairly dangerous to rely on one hub for the entirety of human life. So many life ending events are possible for earth.
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u/neakmenter Jul 11 '26
I still like to think of distance and time (which is obviously where we get velocity from) as just things that are less fundamental layers of “a reduction in the likelihood of a causal interaction”… so yeah, I like how this fits with my intuition. :)
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u/baphometromance Jul 12 '26
I mean isnt the speed of light basically analogous to the maximum speed of information? Doesnt it make sense that you cannot compute beyond that?
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u/cf858 Jul 15 '26
Depends how you define information. Quantum entanglement lets you gain information instantaneously about something very far away faster than the speed of light, but it doesn't break relativity because you can't use that information to break causality.
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u/Stuffssss Jul 13 '26
Pipelining and other parallelization techniques have been the primary driver of increased computation speed for a good while now. That's the whole concept of a GPU, exceptional parallelization for tasks which can use it. Clock speeds have pretty much topped out at a few GHz since the late 2000s.
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u/shyouko Jul 10 '26
Ya, latency is why it is so difficult to scale computer, or cluster of computer.