Physics terminology (split from velocity of a neutrino)

[michel123456]

I am not questionning invariance of C.

 

There are too many concepts here where none is synonym of the other. Frame dependent, relative, constant, absolute etc.

IMHO something can be alltogether invariant and relative.

As an analogy:

When you stand upright at sea level, you horizon is at approximatively 11km away. The distance to horizon is relative, because it comes from you, you are at the centre of vision. The distance is also constant, if you walk to your horizon, the distance will not diminish.

 

I know it is simply an analogy, distance is not velocity, but it is an example where something relative is also constant.

Edited November 10, 2014 by michel123456

[swansont]

Your example doesn't show anything that is invariant. It shows something that is constant for one observer but relative between observers. Constant and invariant don't mean the same thing. One means it is unchanging in a frame, the other means it is unchanging between all frames.

[Sensei]

As an analogy:

When you stand upright at sea level, you horizon is at approximatively 11km away.

 

On Moon or other planet it would be different distance to horizon. It's depending on curvature (radius) of sphere and your height.

Edited November 10, 2014 by Sensei

[michel123456]

 

On Moon or other planet it would be different distance to horizon. It's depending on curvature of sphere and your height.

Correct.

(BTW I looked in wiki the distance on Earth is approx. 5km, not 11)

 

The horizon is the same for all observers that are in the same conditions (on Earth at sea level) no matter their state of motion. If you run to the horizon, you will never catch it. The distance to the horizon does not change.

How do you call that in physics?

Edited November 10, 2014 by michel123456

[swansont]

You can derive it from geometry. You would call that a constant, because you have set all of the variables it depends on to be constant.

[michel123456]

You can derive it from geometry. You would call that a constant, because you have set all of the variables it depends on to be constant.

Agree.

That would be a constant.

But isn't it relative as well, in the sense that there exist no absolute horizon?

[studiot]

Relative doesn't necessarily mean there is no absolute.

 

It means that there is a connection between two quantities that can be expressed as an equation.

 

This may be a subtraction, as with velocities and elevations above sea level.

It may be a ratio (or division) as in my conker is five times as strong as nigel's new one.

It may be a square root as in The increase in radius is the square root relative to the radius.

and really any (mathematical) connection you can think of.

[Dekan]

Suppose we were exceptionally intelligent dolphins. Would we know what a lateral "horizon" was?

 

Probably not. Because when we looked laterally, we wouldn't see a horizon. The lateral, sideways, view, would be too dim and constricted by coral reefs, marine outgrowths and stuff.

 

But - if we looked upwards, towards the surface of the sea - wouldn't we then see a clear, flat, plane horizon - ie, the dividing line between sea and atmosphere?

[swansont]

Agree.

That would be a constant.

But isn't it relative as well, in the sense that there exist no absolute horizon?

 

 

Yes, it's relative because it depends on other variables, and constant because you've fixed those variables.