Prev: Quantum Gravity 357.91: Croatia Shows That Probability of Vacuum Energy Density is More Important than its Vacuum Expectation Value (VEV) of the Hamiltonian Density, in line with Probable Causation/Influence (PI)
Next: Hubble Views Saturn's Northern/Southern Lights
From: PD on 13 Feb 2010 13:44
On Feb 13, 7:29 am, Ste <ste_ro...(a)hotmail.com> wrote:
> I've been absolutely racking my brain (to the point of getting a
> headache) for the last few days about this issue, and it's clear that
> the speed of light (where light is either considered in the form of a
> ballistic photon, or a wave-cycle) cannot, physically, be constant in
> all relative frames, and at the same time be constant when travelling
> between two objects in two different frames. It's a physical and
> logical impossibility.
>
> It's also clear that velocities cannot be additive (in the form of
> speed of bullet+speed of gun), and nor can they be subtractive
> relative to a background medium (in the form of speed of propagation
> in medium-speed of source).
>
> Take an illustration:
>
> A                         C
> B
>
> Where A and B are atoms that pass infinitely close to each other. In
> the illustration, A and B are separated from C by a distance L. A and
> C are stationary relative to each other. B is moving, and approaching
> C at a speed S. A pulse is emitted from both A and B simultaneously
> towards C, at the point when A and B are equidistant from C.
>
> Now, clearly, if velocities were additive, then light from B would
> reach C much quicker than light from A. We don't see that, so we can
> dismiss that immediately.
>
> Next, if velocities were subtractive, like sound, well that seems like
> a compelling explanation for what we see, which is that light from
> both A and B travel towards C at the same speed. But the presence of
> an absolute medium seems to fall down when one considers that, to be
> consistent with observation, the speed of propagation orthogonal to
> the direction of travel must be the same as the speed in the direction
> of travel.
>
> A speed (i.e. a mesure of distance traversed within a period of time)
> cannot possibly be measured constant in all directions within a frame,
> *and* constant between frames, where the frames themselves are moving
> at a speed relative to each other. So how the hell does one reconcile
> this physically?

First of all, it's a mistake to say that velocities must be either
additive or subtractive, as though those are the only two
possibilities.
The reality is that velocities combine this way: v' = (v+u)/(1+uv/c^2)
or this way: v' = (v-u)/(1-uv/c^2).
Now then, the right question might be, why on earth would it be this
way rather than simple addition or subtraction.

Secondly, if you're looking for a diagram that makes sense of this,
you need to be Googling first for something like "worldline in
Euclidean space".
This will show you what the *meaning* of velocity is on the worldline
diagram.
This will also show you *diagrammatically* what it means to transform
the velocity to a different frame and WHY the additive rule would be
expected if the universe had that geometry (disconnected time and
space dimensions).
Then you can find out *diagrammatically* what it means to transform
the velocity if the universe has connected time and space dimensions,
and just a little playing around with the diagram will reveal the
reason for the odd-looking sum rule above.

Robert Geroch's book that I've mentioned to you previously has some
good presentations of these diagrams.
From: PD on 13 Feb 2010 13:45
On Feb 13, 11:51 am, Ste <ste_ro...(a)hotmail.com> wrote:

>
> Not really. I'm still struggling to understand what is happening
> physically to explain these phenomena (which is not helped by the
> dearth of interest in physics in physical, rather than mathematical,
> explanations).

Oh, come now. You appear to have bailed on the discussion of
relativity of simultaneity, which I was doing with purely physical
explanations and a complete lack of math.
I think you're being just a bit disingenuous here.

From: dlzc on 13 Feb 2010 13:59
Dear Ste:

On Feb 13, 6:29 am, Ste <ste_ro...(a)hotmail.com> wrote:
....
> So how the hell does one reconcile
> this physically?

Simple. All you have are light speed signals, one way or another,
being correlated at a single point. Not mental model constrains
Nature, only the human brain struggles with his / her preconceived
notion of "what is going on out there".

David A. Smith
From: Ste on 13 Feb 2010 14:01
On 13 Feb, 18:45, PD <thedraperfam...(a)gmail.com> wrote:
> On Feb 13, 11:51 am, Ste <ste_ro...(a)hotmail.com> wrote:
>
>
>
> > Not really. I'm still struggling to understand what is happening
> > physically to explain these phenomena (which is not helped by the
> > dearth of interest in physics in physical, rather than mathematical,
> > explanations).
>
> Oh, come now. You appear to have bailed on the discussion of
> relativity of simultaneity, which I was doing with purely physical
> explanations and a complete lack of math.
> I think you're being just a bit disingenuous here.

I didn't bail on it. I said I felt that your train analogy had a lot
of extraneous concepts, such as clouds and tracks, and then you didn't
really go on to say anything more about that analogy or about
simultaneity.

And on a slightly separate matter, I admitted that I couldn't make
sense of the speed of light in terms of a stationary medium.
From: PD on 13 Feb 2010 14:11
On Feb 13, 1:01 pm, Ste <ste_ro...(a)hotmail.com> wrote:
> On 13 Feb, 18:45, PD <thedraperfam...(a)gmail.com> wrote:
>
> > On Feb 13, 11:51 am, Ste <ste_ro...(a)hotmail.com> wrote:
>
> > > Not really. I'm still struggling to understand what is happening
> > > physically to explain these phenomena (which is not helped by the
> > > dearth of interest in physics in physical, rather than mathematical,
> > > explanations).
>
> > Oh, come now. You appear to have bailed on the discussion of
> > relativity of simultaneity, which I was doing with purely physical
> > explanations and a complete lack of math.
> > I think you're being just a bit disingenuous here.
>
> I didn't bail on it. I said I felt that your train analogy had a lot
> of extraneous concepts, such as clouds and tracks,

On the contrary, I *agreed* with you that the clouds (which I never
brought up -- you did) are extraneous, as are the tracks, which is
precisely why the velocities of the train with respect to the tracks
are irrelevant.

> and then you didn't
> really go on to say anything more about that analogy or about
> simultaneity.

I'm sorry, read again. I laid out the plan for where we were going
next. Did you not see that?

>
> And on a slightly separate matter, I admitted that I couldn't make
> sense of the speed of light in terms of a stationary medium.

First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13
Prev: Quantum Gravity 357.91: Croatia Shows That Probability of Vacuum Energy Density is More Important than its Vacuum Expectation Value (VEV) of the Hamiltonian Density, in line with Probable Causation/Influence (PI)
Next: Hubble Views Saturn's Northern/Southern Lights