Re: What is a photon

Den 15.06.2025 10:35, skrev Thomas Heger:

Am Samstag000014, 14.06.2025 um 11:33 schrieb Paul.B.Andersen:

Den 13.06.2025 09:55, skrev Thomas Heger:

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Velocity is meant as change of distance per unit of time.
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Since 'distance' is meant as a length of a vector between two points, we need a point 'at rest' in the first place, if we like to measure velocity.
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Since we cannot use empty space itself as reference, we need to define, what we mean by 'at rest'.
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This is actually a little difficult, because 'the universe' or 'the background stars' do not provide any 'natural' anchor for position vectors.
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So, we need to take what we have and that is actually the observer himself, because observers do not move in respect to themselves.
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But: all inertial observers are of equal rights!
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That's why we could use any observer, even hypothetical observers.
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Now this would include, that we measure velocity of something from one point, which rests in respect to the object in question and from another point, which moves with velocity v.
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This would mean: that object is at rest and moving with velocity c at the same time!
>

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When I drive in my car the speed of the car in front of me
relative to me is v(t) = dl(t)/dt where l(t) is the distance
between our cars. Right?
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Does that mean that I am at rest and moving with velocity c
at the same time?
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 When driving your car you usually don't use other cars as reference, but (most likely) the surface of planet Earth.

If you are driving a car and want to measure the speed of the car
in front of you relative to you, your car is obviously the reference.

But that surface does in fact move (actually very fast) and you simply ignore that movement.
 You could, however, consider also that movement, which is caused by rotation of Earth around its own axis.
 But that axis moves, too, but around the sun. And also the sun moves around the center of our home galaxy.
 And even that moves.

Thomas, you are babbling

 Therefore your odometer needs to show a simplified version of your velocity and ignores cosmology entirely.

An odometer measures distance, not velocity.
A speedometer consists in principle of an odometer and a clock.
When you use the speedometer in your car, the car is the reference.
The speedometer measures the speed of the road relative to your car.
v = dl/dt
The distance l is measured with the odometer and the time is
measured with a clock.
The speedometer is stationary in your car, so your car is
the reference, not the road.

 Relative velocities in respect to other cars is mostly not very useful,

The police who drives after you and measure your speed relative to him
with a radar finds it very useful.
-----------------------
But you failed to answer my question:
  When I drive in my car the speed of the car in front of me
  relative to me is v(t) = dl(t)/dt where l(t) is the distance
  between our cars.
  Does that mean that I am at rest and moving with velocity c
  at the same time?
Thomas Heger wrote:
| we measure velocity of something from one point,
| which rests in respect to the object in question
| and from another point, which moves with velocity v.
| This would mean: that object is at rest and moving with
| velocity c at the same time!
The point is:
What is this cryptic statement of yours supposed to mean?
--
Paul
https://paulba.no/