time measurement

Discussion of theories involving time as a dimension, time travel, relativity, branes, and so on, usually applying to the "real" universe which we live in.

time measurement

Postby papernuke » Thu Jan 18, 2007 5:39 am

Is our way of measuring time accurate? As in with the 24 hours in a day and that stuff. Is there a true time of the universe, not Universal Time, which is like military time.
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Postby houserichichi » Thu Jan 18, 2007 5:01 pm

The second is a physical invariant of measurement. As per wikipedia,

Wikipedia wrote:Under the International System of Units, the second is currently defined as 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. This definition refers to a cesium atom at rest at a temperature of 0 K (absolute zero).
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Postby papernuke » Fri Jan 19, 2007 3:22 am

Does that time apply for the entire universe(with the exception of blk holes)?
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Postby houserichichi » Sat Jan 20, 2007 1:55 pm

It applies in a black hole too....to you, assuming you're the one doing the falling into the hole, a second will pass as normal, time will feel like it does just like it does here on Earth. Your watch would still click off a second normally like it does where you are now...it's the time relative to other things that appears to speed up or slow down, but for you the second is still universally the same everywhere.

Addendum: it doesn't really matter when you get close enough to the singularity anyway because the tidal forces will rip you to shreds anyway and you won't have a watch to read off of anymore, but I digress ;)
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Postby papernuke » Sun Jan 21, 2007 3:56 am

WAit, but isnt time slowed down near black holes?
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Postby Nick » Sun Jan 21, 2007 6:08 pm

Paper Nuke wrote:WAit, but isnt time slowed down near black holes?


Yes, time stops completely at the core of a black hole. A second at the black hole is an infinite amoung of time; but since time has stopped for everything at the black hole, your personal time would have stopped as well.
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Postby Keiji » Sun Jan 21, 2007 7:06 pm

Of course, it doesn't make any difference, as nobody would be able to survive long enough to know what happened in a black hole ;)
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Postby wendy » Mon Jan 22, 2007 7:41 am

The duration of a second, is equal to 983574900 feet.

Time is a purely local concept. One might understand that there is problems with "simultaneousness" at a large scale event, and that the space-time metric and the exact nature of space play a role in the sequencing of events that occur at different space-time coordinates.

The UTC is "universal" in the sense that all countries recognise it. It's just another name for a different kind of clock that pumps out seconds.

One should note also that while the second is atomic, the day is kept to its astronomical entity, and accordingly, one adds "leap seconds" when there is a buildup of error. So the mean year (of 365.2425 days), is not 31556952 seconds (which is what 365.2425 * 86400 is), but a somewhat different number of seconds.
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Postby PWrong » Tue Jan 23, 2007 2:22 pm

The duration of a second, is equal to 983574900 feet.

What?
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Postby Nick » Tue Jan 23, 2007 4:54 pm

PWrong wrote:
The duration of a second, is equal to 983574900 feet.

What?


I think she was trying to prove the point that time cannot be properly measured since it's all relative. I think.
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Postby houserichichi » Wed Jan 24, 2007 3:24 am

Depends what your units are. Those are called natural units (and honestly, who the hell uses feet anymore anyway ;))
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Postby papernuke » Sat Jan 27, 2007 4:08 pm

My brother does, but i use metric.
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