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The Last POWER1 CPU on Mars Is Dead

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Re: The Last POWER1 CPU on Mars Is Dead

#61

Post by dfox »

wbl wrote: post #42
echlebek wrote: post #34

Earlier quoted context omitted.

That's actually not true if you're using SI units for seconds. "The SI unit of time is the second (s): The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom." I'm not a physicist, but I think that's a universal definition - the rate of the periods should be constant everywhere in the universe. S…

You are forgetting relativistic effects.

Because SI itself assumes that you and whatever you are measuring is in same relativistic frame of reference. When you start to take relativity into account the whole system breaks down horribly.

Re: The Last POWER1 CPU on Mars Is Dead

#62

Post by Rebelgecko »

wlesieutre wrote: post #41
teraflop wrote: post #32

Earlier quoted context omitted.

I don't think the relativistic effects would be a problem in practice. You can synchronize clocks on other planets to the UTC or TAI reference time, which are already specified in terms of the Earth's reference frame. Because of relativity, clocks on other planets would very slowly drift relative to UTC on Earth. But the drift is on the order of a few parts per billion (see e.g. [1]) which is comparable to what you'd…

If I did my math right that's 0.178 seconds per year. As long as everyone's handling time the same way you shouldn't have a problem, but it's enough to be noticeable if someone forgets about it. I suppose the more noticeable oddness for most people would be that the speed-of-light delay in communications from Earth to Mars varies so much. Around 3 light minutes up to 22 depending on where they are in their orbits.

That's around what I got from my back of the envelope Math too (well, I got around 300ms/year). Small enough where you can adjust a leap second everyone few years to take care of the drift. Kind of like converting between UTC, TAI, and UT1.

It may need to be compensated for when receiving transmissions between the planets, but I don't know enough about RF to judge how meaningful the difference is. There was a spacecraft (I think Huygens?) that actually had problems with Doppler shift. I think in that case they forgot to take it into account entirely, so it wasn't that they just forgot the relativistic component.

Re: The Last POWER1 CPU on Mars Is Dead

#63

Post by james_s_tayler »

yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

I vote we switch to Metric Time. That'll solve all our problems.

Re: The Last POWER1 CPU on Mars Is Dead

#64

Post by CydeWeys »

JumpCrisscross wrote: post #9
yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

> Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? This fundamentally cannot exist. Any "universal" system would drift for observers on different planets. Having different times in New York and New Delhi isn't the worst right now; doing a calendar look-up for the time on Mars isn't as neat. But given we won't have real-time communication, it isn't as big of a problem e…

They won't drift if the observers correct for their corresponding known differences. E.g. we know the orbital speed of the planets, so plug those into general relativity and you would know how fast your local time is moving vs time on another planet, and can thus compensate.

Re: The Last POWER1 CPU on Mars Is Dead

#65

Post by CydeWeys »

wlesieutre wrote: post #18
dahfizz wrote: post #8

Earlier quoted context omitted.

I don't really see the problem with standardizing on 'seconds since the epoch' for any interplanetary communication and having clients convert to something more meaningful to humans. Any other "universal" time format will be just as meaningless when days and seasons are all different lengths.

At a certain point of accuracy you run into issues with this - seconds don't pass at the same rate due to relativistic effects (both speed and gravitational). An example we already deal with is GPS satellites orbiting Earth. Their clocks tick a little bit slower on account of how fast they're orbiting, and tick a bit faster on account of being further up Earth's gravity well. The gravitational effect is stronger, and…

GPS satellites already control for relativistic effects. Their required accuracy is so high that they wouldn't work without doing so.

You would simply also correct for relativistic effects caused by the orbits of different planets, and boom, you have a pretty consistently defined time that is valid across the entire solar system.

Re: The Last POWER1 CPU on Mars Is Dead

#66

Post by weberc2 »

JumpCrisscross wrote: post #9
yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

> Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? This fundamentally cannot exist. Any "universal" system would drift for observers on different planets. Having different times in New York and New Delhi isn't the worst right now; doing a calendar look-up for the time on Mars isn't as neat. But given we won't have real-time communication, it isn't as big of a problem e…

You can factor the drift into the time expression or you can simply agree to use earth time or Martian time or any other time. No fundamental need to base time units on Mars on Martian astronomy.

Re: The Last POWER1 CPU on Mars Is Dead

#67

Post by twic »

yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

> Something that is a little more useful than "seconds since UNIX epoch"

Milliseconds since UNIX epoch!

Re: The Last POWER1 CPU on Mars Is Dead

#68

Post by oso2k »

gonehome wrote: post #54
JumpCrisscross wrote: post #9

Earlier quoted context omitted.

> Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? This fundamentally cannot exist. Any "universal" system would drift for observers on different planets. Having different times in New York and New Delhi isn't the worst right now; doing a calendar look-up for the time on Mars isn't as neat. But given we won't have real-time communication, it isn't as big of a problem e…

Somewhat comically J.C.R Licklider's first proposal for what became the internet was titled the Intergalactic Computer Network. He later said he did this because when the project is inevitably downsized it would at least cover the earth. Interplanetary internet designs and peering are interesting problems to think about though. https://en.wikipedia.org/wiki/Intergalactic_Computer_Network

There are real, standardized protocols [0] for this sort of thing, now. Early in my career, when I worked at JPL/NASA, I did a bit of work to test these protocols on Linux in a simulated Network of spacecraft. Fun stuff!

[0] https://en.wikipedia.org/wiki/CCSDS_File_Delivery_Protocol

Re: The Last POWER1 CPU on Mars Is Dead

#69

Post by emilfihlman »

yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

Any time period in itself is arbitrary. Our seconds, minutes, hours and days, years are sorta okay.

Though I do see the irony with at the same time shaming imperial units.

We'll highly likely stick with second as the base unit but create base 10 multiples on that .

Re: The Last POWER1 CPU on Mars Is Dead

#70

Post by magduf »

make3 wrote: post #16
yingw787 wrote: post #5

Might be O/T, but I found it really interesting how they mention "5,352 Martian solar days". Do we humans have plans in the pipeline for a universal time standard we can use wherever we are? Something that is a little more useful than "seconds since UNIX epoch" but something a little less terrestrial than UTC? Or is time going to be based wherever we land or travel (e.g. divide up Mars into time zones upon colonizati…

must be Terran time, as literally all humans are currently either on Earth or orbiting around Earth, so literally everyone can relate

>as literally all humans are currently either on Earth or orbiting around Earth

The fact that this phrase of yours is literally true, and it's already 2019, makes me very sad.

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