http://apnews1.iwon.com/article/20060908/D8K0V91G2.html

a 10-billionth of a second is just too long a time between ticks of a clock. And it really makes a difference that a clock in mile-high Denver ticks faster than another at sea level. (Time itself passes more quickly when gravity is reduced.)

I find this intriging, is it true?

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http://apnews1.iwon.com/article/20060908/D8K0V91G2.html

a 10-billionth of a second is just too long a time between ticks of a clock. And it really makes a difference that a clock in mile-high Denver ticks faster than another at sea level. (Time itself passes more quickly when gravity is reduced.)

I find this intriging, is it true?

Yup.

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Reality Internet Personality

So time must be "flying" in the vast weightlessness of space. I wonder how this affects astronomical sciences and whether this has been accounted for in our observations of all things across space and time...

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Kolch - Crunching for the BOINC@Australia team since July 2004.
Search for your own intelligence...

[edit]Ooops[\\edit]

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Kolch - Crunching for the BOINC@Australia team since July 2004.
Search for your own intelligence...

So time must be "flying" in the vast weightlessness of space. I wonder how this affects astronomical sciences and whether this has been accounted for in our observations of all things across space and time...

Sattelites such as those used in the GPS network routinely correct for time differences due to orbital effects. Especially on the military bands of the various systems.

Regarding the higher precision (shortened):

Bergquist and others have demonstrated a better way to make them, an approach he figures will eventually replace the technology that has reigned for 50 years. [...] The new clock technology may not only displace the old, but it may also force a revision in what physicists regard as the definition of one second.

Bergquist figures that with further development, the new technology will become at least 100 times as accurate as the standard kind of clock could ever be.

The current definition, like the ultra-precise clocks now in use, is based on microwaves and the behavior of a cesium atom. The nucleus of a cesium atom switches back and forth between two physical states when it is hit with microwave radiation of a particular frequency. That frequency is the "tick" of current clocks. One second, to physicists, is 9,192,631,770 such ticks.

The new "optical" clocks instead hit an atom with a laser beam, finely tuned to a certain frequency. Laser "ticks" come about 100,000 times faster, and thus could become the new basis for the definition of a second.

The timekeeping seems also to keep some sort of Moore's law, but in not-so-fine steps: instead increasing the resolution 2 x in 18 months, rather some 100 x in 50 years.

Peter

(Time itself passes more quickly when gravity is reduced.)

Unless I'm totally on the wrong track, a mechanical or electrical clock may be faster or slower under the effects of gravity, but "real" time will surely always elapse at the same rate, regardless of what any indicating devices say?

Maybe better to talk about the clock's perception (sense) of time?

I've read that people on a long space journey will return to earth younger than those they left behind, buts thats supposed to be an einstein effect of the speed they travel at not time?

Yes.

BTW, was it already proved on satellites? And the difference between speed and gravity?

Peter

Unless I'm totally on the wrong track, a mechanical or electrical clock may be faster or slower under the effects of gravity, but "real" time will surely always elapse at the same rate, regardless of what any indicating devices say? I've read that people on a long space journey will return to earth younger than those they left behind, buts thats supposed to be an einstein effect of the speed they travel at not time?

Chris

The time in your frame of reference does not appear to speed up or slow down. There is not such thing as absolute time or absolute space (real time?)..time itself does elapse at different rates for different observers...but yes..time runs slower for people who travel at faster speeds.

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Reality Internet Personality

So time not only runs slower when it is freed from the terrible oppression of gravity, it also runs slower when travelling fast.

So travelling fast through space would have a doubled effect.

Only thing is, i imagine there might be a spacecraft travelling very fast and there are space travellers on board. Only they aren't moving exactly... They're sitting around just doing their normal things. Everything seems normal to them except that when they look out the spacecraft window, everything outside the spacecraft appears to slow down.

Another way of saying this; when i drive my car, am i moving at 100km/h? Or am i sitting stationary in the driver's seat?

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Kolch - Crunching for the BOINC@Australia team since July 2004.
Search for your own intelligence...

Only thing is, i imagine there might be a spacecraft travelling very fast and there are space travellers on board. Only they aren't moving exactly... They're sitting around just doing their normal things. Everything seems normal to them except that when they look out the spacecraft window, everything outside the spacecraft appears to slow down.

No. I think they are supposed to see everything outside happening amazingly fast for them.

Another way of saying this; when i drive my car, am i moving at 100km/h? Or am i sitting stationary in the driver's seat?

You are moving at 100km/h related to the road. The question is whether and how fast does the road move with you...

(I'm sorry for stealing the thread.) I was thinking about if some spacecraft would travel at 0.95 light speed from Earth to e.g. Pluto, the passengers should feel they are getting pretty fast there (I do not remember the equations for time and speed). Then in the middle of the road, maybe somewhere around Saturn, they will send some courier with small ship back to Earth. He is also capable to travel with the same high speed. A) does it mean he have to break twice the speed (relative to Earth) in order to travel 0.95LS towards Earth? and B) is it the speed difference between the traveller and some origin of universe which is important for his local time speed, or the time speed is relative between two objects moving at some relative speed between them? (Uffff.)

Peter

[quote]No. I think they are supposed to see everything outside happening amazingly fast for them.[\\quote]

Actually as you yourself said, its due to the apparent relative nature of speed that this confusion occurs. And yes we have pretty much hijacked the thread, sorry.

Speed is not truly relative though. Given that distance and time are known constants, and speed is measured in distance per timespan.

So to the occupants of a fast moving spacecraft, everything appears to move by very fast (as you pointed out) but in the time it takes them to get from one side of the solar system to the other only a few seconds (i could look up the exact time but i can't be bothered) have passed.

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Kolch - Crunching for the BOINC@Australia team since July 2004.
Search for your own intelligence...

Actually as you yourself said, its due to the apparent relative nature of speed that this confusion occurs. And yes we have pretty much hijacked the thread, sorry.

Speed is not truly relative though. Given that distance and time are known constants, and speed is measured in distance per timespan.

So to the occupants of a fast moving spacecraft, everything appears to move by very fast (as you pointed out) but in the time it takes them to get from one side of the solar system to the other only a few seconds (i could look up the exact time but i can't be bothered) have passed.

The whole point of relativity is that time and distance are not constant.

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Reality Internet Personality

I can assure you that 100km is 100km no matter how you measure it, where you are, how fast you travel it, what its made out of... If you could plot a path between two points in the universe the distance between them is always the same, unless you move the points, which is a different story. Even if the points are the same and you travel a 100km circle to return the the same point, you've travelled 100km.

As for time not being constant, that's a whole barrel of works i'm not sure i want to think about.

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Kolch - Crunching for the BOINC@Australia team since July 2004.
Search for your own intelligence...

I can assure you that 100km is 100km no matter how you measure it, where you are, how fast you travel it, what its made out of... If you could plot a path between two points in the universe the distance between them is always the same, unless you move the points, which is a different story. Even if the points are the same and you travel a 100km circle to return the the same point, you've travelled 100km.

As for time not being constant, that's a whole barrel of works i'm not sure i want to think about.

100 km is not 100km no matter how you measure it.

Here is an easy read on The Lorentz Contraction.

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Reality Internet Personality

I can assure you that 100km is 100km no matter how you measure it, where you are, how fast you travel it, what its made out of... If you could plot a path between two points in the universe the distance between them is always the same, unless you move the points, which is a different story. Even if the points are the same and you travel a 100km circle to return the the same point, you've travelled 100km.

As for time not being constant, that's a whole barrel of works i'm not sure i want to think about.

100 km is not 100km no matter how you measure it.

Here is an easy read on The Lorentz Contraction.

Isn't the universe also expanding? Wouldn't that mean that two points in space that are exactly 100km apart immediately startmoving away from each other?

I can assure you that 100km is 100km no matter how you measure it, where you are, how fast you travel it, what its made out of... If you could plot a path between two points in the universe the distance between them is always the same, unless you move the points, which is a different story. Even if the points are the same and you travel a 100km circle to return the the same point, you've travelled 100km.

As for time not being constant, that's a whole barrel of works i'm not sure i want to think about.

100 km is not 100km no matter how you measure it.

Here is an easy read on The Lorentz Contraction.

Isn't the universe also expanding? Wouldn't that mean that two points in space that are exactly 100km apart immediately startmoving away from each other?

That would be a different effect from Lorentz contraction.

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Reality Internet Personality

Here is an easy read on The Lorentz Contraction.

I'm a bit confused now. It is a mix of relativity and Doppler effect what the Time Dilation page suggests. But all-in-all I understand it so that the time measurements (in the moving objects) should indeed be related to some steady origin and can't be easily compared between each other while moving.

Peter

Isn't the universe also expanding? Wouldn't that mean that two points in space that are exactly 100km apart immediately start moving away from each other?

Surely that would depend upon their relationship to the centre of the "big bang".

If they were in line astern they ought to move together, therefore the distance between them should stay constant. However if they were side by side, then presumably they would move apart angularly???

Anyway, measuring a distance between two points in space is probably only accurate at the moment it was measured. Who knows what gravitational effects or other forces are out there to change that later.

Chris

From what I understand there is no 'centre' of the big bang. Everything is moving away from everything else and not away from a central point. In fact it doesn't make sense to have a central point as before the big bang there was no place for there to be a central point. Space-Time itself was created in the big bang.

So yes, the distance between things is increasing..but your ruler will be increasing by the same amount so it doesn't make any difference to your measurement.

I think the temperature of an object would have a more obvious effect on the size of it than the gravitational forces acting on it...but you might want to check out the Einstein@home project to see how they go about detecting such things.

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Reality Internet Personality

Here is an easy read on The Lorentz Contraction.

I'm a bit confused now. It is a mix of relativity and Doppler effect what the Time Dilation page suggests. But all-in-all I understand it so that the time measurements (in the moving objects) should indeed be related to some steady origin and can't be easily compared between each other while moving.

Peter

What steady origin? I don't understand.

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Reality Internet Personality

From what I understand there is no 'centre' of the big bang. Everything is moving away from everything else and not away from a central point. In fact it doesn't make sense to have a central point as before the big bang there was no place for there to be a central point. Space-Time itself was created in the big bang.

Well this is how I've always understood it.

The universe has always been there, complete with space and time, always has been, and always will be. It is infinite with no beginning and no end, and goes on forever. We have difficulty in visualising that as we live in a finite world as against an in-finite one.

At some point in the past, in our local part of the universe, all the local matter condensed in a single place, and became so compressed that it exploded, the results of which we can still detect today. There may be other parts of the universe that have had similar explosions.

The theory apparently goes that, the universe itself is in "steady state" but various parts of it occasionally go into different mode. Whether it's "expand/contract" or "expand for ever" no-one knows.

Phew!!!

It only goes on forever in the sense that a circle goes on forever. If you go far enough in one direction you will get back to where you started from. In other words, space itself if curved...not flat. It just looks flat locally, the same way the Earth looks flat to us as we crawl about on it's surface.

When we look out from out planet it any direction we see that everything is moving away from us..we know this because all the light reaching us from other stars and galaxies has had it's wavelength shifted towards the red end of the electromagnetic spectrum. (The Doppler red-shift).

So either we are at the centre of the universe and at the heart of the big bang (very, very unlikely)..or where ever you stand in the universe everything looks the same. So in other words..the universe itself is expanding. An analogy might be two points drawn on a balloon will move away from each other as the balloon inflates.

Extrapolating backwards, we can assume that at one time everything must have once all been at the same point..this is how physicists arrived at the idea of a big bang.

You are right that there are still discussions as to whether the universe will expand for ever (an open universe), someday just stop expanding or stop exapanding and collapse back on itself to a singularity. (and last I heard the rate of expansion was actually speeding up!)

However, the big bang was not an event localised in space. The universe was (theoretically) created in that moment. Time and space were created in that moment (so there was no 'before' the big bang).

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Reality Internet Personality