Horizon BBC2 - What's The Time.....

[mosaix]

Interesting program tonight (although Horizon is still a shadow of its former self).

The discussion was 'time' and exactly what it is.

I'm still baffled. I'm sure I'm wrong, but time, as a concept, seems to me to a human construct.

In the program they were explaining how gravity has an effect on time, that atomic clocks can vary, one to another, according to their proximity to massive objects.

But surely what is being affected isn't time, but what we choose to measure or represent time. i.e. what is being observed is the effect of gravity on atomic clocks.

Can anyone help me out on this?

[Dave]

I didn't see that programme (it sounds like I should have) but I would say that as atomic clocks work on the rate of decay of unstable isotopes, and that decay is a function of probability, then they must be a constant. (Gravity can not change the probability that an atomic isotope will decay or not.) If anyone disagrees, please help me too!

So, it would seem to me, from your post, that if the speed of atomic clocks is affected by Gravity, then Gravity is indeed having an effect on Time.

You need to dispel our human notions of Time. We see Time as a constant ever going forward second by second, when in reality it is just a fourth dimension of Space, after length, width and depth. It is difficult concept to get your head around, but not really any more difficult that believing that things only fall to Earth because of Gravity, and that there is no such thing as up or down.

It gets more difficult to deal with the concept that there may be as many as fourteen dimensions. To a Being that could actually see in all fourteen dimensions, to them, the whole history of the Earth wouldn't even be what a two-dimensional spot on a piece of paper is to us.

[Ursa major]

Did it mention any of the weirder stuff - like those folk who propose the idea that time is really just like another dimension, except thatr we somehow can only observe travel in the one direction?

[Nik]

Um, I've only seen a portion of program due family interrupt...

( Recorded, so we'll watch it tomorrow-- If we can spare the time ;-)

Okay, IIRC, the classic example for time dilation at near-relativistic speeds is muons formed in upper atmosphere by cosmic ray strikes. Their half-life is so short, few should reach surface. Many do. They're travelling so fast, their 'fuze' runs slow by our reckoning...

IIRC, the ultimate example for time changing near mass is the edge of a black hole...

A more practical example is GPS system. IIRC, if the system does not correct for transmitters' motion within gravitational field, position fixes come out wrong. They also must correct, IIRC, for second-order effects of Earth's rotating mass such as frame dragging...

Time, of course, is relative. Flies when fun, drags when you're killing it...

[Dave]

I don't see that as a problem (but I only did Physics to A Level and we never covered this).

If you were in a car driving at 70 mph for the whole of your life you would only see length in one direction too.

(I'm saying that there is a vector and a velocity - for Time for us, that is always positive and constant. Someone correct me if I'm wrong here. Otherwise, there is a story potential - someone who can change velocity and direction in time.)

[TheEndIsNigh]

Originally Posted by mosaix

But surely what is being affected isn't time, but what we choose to measure or represent time. i.e. what is being observed is the effect of gravity on atomic clocks.

Can anyone help me out on this?

Ah mosaix. Sanity in a world of chaos. I'm with you on this one.

It's like the particles that are supposed to be unable to reach Earth from the sun because their half life is too short. This is taken to be a proof the time slows down for things travelling at near light speeds.

Now why not explain this by supposing that all sorts of weird things happen to atomic structure when particles travel at near light speeds instead.

[Ursa major]

Originally Posted by Nik

Time, of course, is relative. Flies when fun, drags when you're killing it...

I heard a short section of a Radio 4 programme that dealt with our perception of the passage of time. (The programme was between 16:00 and 17:00 on a Wednesday a month or two back.) My memory of what I heard is a bit fuzzy, but I think it had something to do with the way the brain records experiences.

[TheEndIsNigh]

Ah, Was it like the program where they dropped sudents off a ten storey crane with no harness. They could read the flashing time on an led display easily.

Now that was funny. Especially the faces when they said they had to re do it because they hadn't done it right.

http://www.youtube.com/watch?v=RjlpamhrId8

[Ursa major]

That sounds like the one. I think. I don't recall "the faces", as my radio doesn't have pictures.



(But then I was listening on the car radio and it wasn't a very long journey. )

[mosaix]

One thing that I've never heard before is that Einstein said that we are travelling through time at the speed of light. How weird is that?

[TheEndIsNigh]

Ursa, it's time you upgraded that old steam radio for one with valves.

I stuck the link in the last post, possibly before you had chance to see it.

[Nik]

We managed to watch the rest of the program tonight, albeit with umpteen re-winds and shouting...

The notion that time runs slower at (relative) speed and in a gravity well / near-mass prompted much of the shouting.

Certainly, the notion makes my head spin, even without frame-dragging which, mercifully, was not mentioned by name...

And, what happened at/before the Big Bang ? Who smacked the branes together ? Be funny if our 13 point summat billion years of universe was just the flaky fall-out from a supra-cosmic fender-bender...