Time dilation

[Anders]

2320AD claims (p. 310) that

"There is a subtle time distortion involved with the stutterwarp drive operation, such that clocks on the vessels are out by approximately 1 second per light year once they’ve finished their voyage, compared to local clocks using Sirius as an astronomical reference point. No one knows the cause of the apparent time-dilation, but apart from having to reset
timepieces it doesn’t cause any problems."​

Hmm, what's the deal with this? First, I doubt any anomalies with the stutterwarp wouldn't be heavily investigated - any apparent oddness might be the key to a better drive or understanding physics better. Second, why Sirius as reference point? The sun is a far more natural one.

That there might be time dilations with stutterwarp use is not strange: given that "instantaneous" and "simultaneous" doesn't have any meaning in relativity it may just be that each jump moves the ship (relative to the original reference frame) not just a distance but a tiny amount forward in time; this is just as likely as it not doing it - and for a passing observer at another speed the jumps will look simultaneous or have another time difference. It is just that relative to the local velocity field they have a small time component.

[ Any FTL drive is a potential time machine after all. The second could just as well have been lost as gained. As I handle it, micro-experiments have confirmed that one can indeed do time travel with stutterwarps, it is just that the Novikov quantum self-consistency principle holds so paradoxes are not possible. To send an entire ship back in time requires relativistic speeds, something that has not been achieved in 2320 - and the Novikov principle suggests that it would be pretty pointless. ]

Setting up interstellar time is an interesting challenge. The trick is to use the speed of light, since it is the same for everybody, regardless of how fast they (or their solar system) are moving. Ignoring general relativity, a simple method would be to send a radio signal from Earth to all other systems. If the signal is sent at January 1 2300 00:00 GMT and you know you are exactly ten lightyears away when it reaches you, then it must be January 1 2310 GMT (OK, I'm ignoring leapyears, leap seconds and the other awful mess of actual timekeeping). So finding exact positions of every system and world together with a few timing signals to set local atomic clocks (with adjustments for gravitational time dilation, relative motion and other messy factors) would enable to set up a universal human time (Temps Atomique Interstellar, run by the International Bureau of Weights and Measures (BIPM)). Using the signals from millisecond pulsars allows independent verification that everything is consistent to a high precision. The local TAI time can then be used to set the local universal coordinated time system, from which local timezones can be derived.

To sum up, I think the extra second is likely not mysterious at all, and I don't think Sirius has anything to do with it.

Added later: here is a paper showing just how complex timekeeping is across an interplanetary network.

 

[Plankowner]

Sirius might make sense just from the point of view that it is a bright star, clearly visible within explored space. By the time you get 10-20 lightyears from Earth, the Sun is pretty dim.

 

[Anders]

If you are using it as a reference you are using a telescope, and then the sun is easy anywhere in human space. While I can imagine using a star as a coordinate origin, it seems odd to select a multiple star that is moving along an elliptic orbit over a single star that is just staying in one place. Especially one that is important to humanity and already is the origin of a whole bunch of coordinate systems.

 

[Doyle Hunt]

In order to detect subtle differences like that cited, you have to be able to compare a hyper-accurate chronometer that made the journey to one that didn't. Which means you either have to make a round trip and come back to a chronometer that never moved, or a time-coded signal has to be sent from your point of origin to your destination. The former is far more likely than the latter, because who wants to wait several years for a signal to catch up to you just to synchronize clocks?

So, why Sirius? Perhaps it's simply that's where the ship that discovered the phenomenon left from (and returned to), and where the comparison was made. It needn't have anything to do with Sirius being a time reference for the whole of explored space.

The most likely time reference for the whole of explored space is probably a pulsar anyway, as that's the only regularly repeating signal guaranteed to be visible everywhere.

 

[Anders]

Pulsars are pretty good clocks, but they do wind down. Fortunately most of the slowing is again extremely reliable, so absent the occasional glitch one can use them to measure the rate of time (especially since one uses data from many known pulsars). The two main problems is that there is timing noise which is larger than current atomic clock accurancy, and that it is nearly impossible to synchronize with pulsars - the glitches are not terribly exact, lasting many milliseconds.

This makes human-produced timing signals invaluable, since they can be sent (using a big radio transmitter or interstellar laser) with a pattern that makes it easy to get an exact time (and estimate of relative speed through the Doppler effect).

As for Stutterwarp glitches, doing the roundtrip is going to be the best way of testing it. There are a lot of important things you can learn by doing this (think of parallel transport and the Riemann tensor in differential geometry), so I expect that one of the very first uses of the early unmanned ships was to carry sensitive instruments on roundtrips to check how much clocks, gyroscopes, atomic spins and whatnot were affected by the length, area and surroundings of the trip. There is going to be 200 years of intense study of this area.

 

[Colin]

How about this, then:

The time differential is minor enough that, in day-to-day use, it is effectively inconsequential. However, some systems require accurate clocks for the purposes of navigation and Link network authentication and synchronization. The systems of Col Mountain, Beowulf, Beta Canaum, Ellis and Niebelungen all have atomic clocks synchronized to the Master Time System, located on Earth's moon, and maintained by the Orbital Quarantine Command. All of these system-wide broadcast clocks can update and synchronize a ship's clocks once they pass the ftl shelf.