# The Naked Scientists Forum

### Author Topic: Do we know exactly what time is?  (Read 24076 times)

#### evan_au

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##### Re: Do we know exactly what time is?
« Reply #75 on: 04/11/2014 09:25:52 »
Slightly off-topic (sorry):
Quote from: JeffreyH
Reflection and refraction follow definite paths....  This is the concept I have a problem with. Application of the uncertainty principle should mean that this path deviates and yet it doesn't.

The design of optical telescopes takes into account of the fact that a photon which has reflected from a mirror (or been refracted by a lens) can be detected in a range of locations, making images of stars blurry.

You can constrain the amount of deviation by making the mirror larger (or the lens larger, for a refracting telescope). When building telescopes, Bigger is Better!

Deviation of photons from the "classical" laws of reflection and refraction is a fundamental part of quantum theory.

#### phyti39

• Jr. Member
• Posts: 45
##### Re: Do we know exactly what time is?
« Reply #76 on: 04/11/2014 20:05:19 »
Quote from: phyti39
Time is a scalar, and has no direction, so there is no arrow of time.
I recommend that if you wish to delve into the physics of special relativity that you learn the mathematical terms correctly. This won't be possible unless you pick up a good textbook on special relativity that explains it using tensors. Tensor analysis is the language of relativity, and hence the math that you should learn. May I inquire as to the level of math that you're familiar with?

The term scalar as you used it comes from elementary school math and science textbooks. It that sense it means a number, real or complex. In tensor analysis it means something else, i.e. A scalar is a tensor of rank zero. This means that it's a number which remains unchanged upon a valid change of coordinates. For example; if you were working in special relativity and using Cartesian coordinates for your spatial coordinates then the coordinate transformation from one inertial frame to another, which is in standard configuration with the original one, is referred to as a Lorentz Transformation. So a Lorentz scalar is a number which remains invariant (i.e. unchanged) upon a Lorentz transformation.

I mention it so that you learn this early on. If you continue to discuss relativity with learned physicists then you'll have to learn the jargon.
Time as a derived number, distance/speed, is a variable. The Lorentz tranformation of t results in a different value for t', for relative motion.
You can do SR using algebra!
I'm not here to impress anyone, so my level of math is irrelevant.
I don't expect to discuss relativity with learned physicists on a public forum.

#### yor_on

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##### Re: Do we know exactly what time is?
« Reply #77 on: 04/11/2014 20:09:41 »
No Phyti, you're correct in defining measures as inventions of the human mind. Without them physics won't exist. But they work and they give us the ability to predict. So they are not 'arbitrarily' made even though you can change their measures.

#### yor_on

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##### Re: Do we know exactly what time is?
« Reply #78 on: 04/11/2014 20:19:34 »
And Pete isn't as hard as he sounds sometimes. If you want to catch a glimpse of the math you need to read his thoughts and ponder :) He's a asset to us all and we should treat him as that. Just as some other guys here,  and you will see them with discussing, I think myself that we have a good blend of minds here.

#### yor_on

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##### Re: Do we know exactly what time is?
« Reply #79 on: 04/11/2014 20:32:25 »
All in all. TNS is probably the best place i know, although I've seen some very close to it. But, we still have that glimmer of humility hiding behind our convictions, and that is in my mind, what science is about, not bullying, talking.
=

And that goes especially for you moderating.
Keep on doing the work you do.

And now I will define 'c' as something similar to a turtle, I'm positive you will agree?
« Last Edit: 04/11/2014 20:47:27 by yor_on »

#### PmbPhy

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##### Re: Do we know exactly what time is?
« Reply #80 on: 04/11/2014 22:26:51 »
Quote from: phyti39
Time as a derived number, distance/speed, is a variable.
What do you mean by a "derived number"?

Quote from: phyti39
The Lorentz tranformation of t results in a different value for t', for relative motion.
Yep. I'm well aware of that. There are two measures of time in relativity. One is called proper time and the other is called coordinate time (or simple "time"). Proper time is the time as measured on a clock which passes through the two events of concern while moving on a geodesic. The coordinate time isn't. The proper time between two events is a Lorentz invariant whereas the coordinate time between the same two events isn't.

Quote from: phyti39
You can do SR using algebra!
Yep. I'm well aware of that.

Quote from: phyti39
I'm not here to impress anyone, so my level of math is irrelevant.
I never assumed that you were. I was merely pointing out a small point on the definition of what the term "scalar" means in SR. That's all. :)

#### phyti39

• Jr. Member
• Posts: 45
##### Re: Do we know exactly what time is?
« Reply #81 on: 05/11/2014 19:38:49 »
All in all. TNS is probably the best place i know, although I've seen some very close to it. But, we still have that glimmer of humility hiding behind our convictions, and that is in my mind, what science is about, not bullying, talking.
=

And that goes especially for you moderating.
Keep on doing the work you do.

And now I will define 'c' as something similar to a turtle, I'm positive you will agree?

I would like to believe that the original intent of science forums was similar to that of "Scientific American", to present complex ideas in terms understandable to the common person with limited technical knowledge. Some have drifted away from that purpose. Those in their specialized fields have their own resources for staying current.

I trust your recommendation is true.

#### The Naked Scientists Forum

##### Re: Do we know exactly what time is?
« Reply #81 on: 05/11/2014 19:38:49 »