« on: 22/08/2021 16:31:55 »
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this gives a momentum pressure of between 3.33 x 10^-6 N/m^2 and 6.67 x 10^-6 N/m^2The Crooke's Radiometer, or "light mill" lets you test this calculation.
depending on full absorption to perfect reflection, of the light energy received.
The plumb line only hangs vertically at the equator,For a particular definition of vertical. (essentially: "points to the middle of the Earth").
Er, no it doesn't. Gravity (G, in black) acts perpendicular to the earths surfaceYou have assumed a spherical Earth- often a reasonable start, but not in this thread about the Earth not being a sphere.
I was quoting directly fromHmm, OK.
The sudden disappearance of the sun is much more like an example situation to help visualise something about GR. It simply doesn't fit the criteria to be considered a "thought experiment" (IMHO).I agree, but I am pretty ambivalent about it's use.
This is a quality resource and it has kept me occupied for hours. Thank you, thank you. I think you've already pulled the text that is most relevant to this forum thread and put it directly into your earlier post.John is one of those really nice guys who is also an excellent researcher and thinker. You should find something on his site about thought experiments in general. Lots of good material and he’s happy to share.
I don't seem to have much disagreement with or from you, Colin.
Any student wishing to follow this example through more carefully with some Mathematics can find a way to provide that acceleration to the sun. They can add stiff strings, photon rockets or high momentum incoming ping-pong balls if they need to. The main thing is that they don't hit a wall that stops them proceeding with the Mathematics as soon as they look at the E.F.E. and realise that the proposed stress-energy tensor isn't even continuous let alone differentiable.
I think it is a mistake to characterize gravity as 'action' at all. It's a field, not something that radiates towards us.I think you, like me, enjoy looking at physics from different perspectives and use the most appropriate at the time. I remember as an undergrad we were set the exercise of deriving Newton’s laws from GR in the weak field limit, a useful reminder that in the approximations they are still valid.
In principle you can derive a relativistic mass for the photon, but this is not often used nowadays.Would you care to put a number to the mass of a photon?Think you can put a value on the equivalence substituting hf for E in the famous equation
Hi allIs there any method that you can think of that could achieve this? Have a stab at it.Similar to the sodium lamp, I believe it would be possible to derive the speed of light using the red/blue shift due to interaction of light with a gravitational field, for example
Hi all"Direction of relative" does not parse. If you mean direction of motion, the answer is no, it matters not. In SR, time dilation relative to inertial frame F is a function of your speed relative to F, and speed, being a scalar, doesn't have a direction.
Halc can I please just clarify your points in regards to;Quote from: HalcAll clocks are affected by these things. Atomic clocks are in no way special in this way. Paint peels slower relative to a frame in which it moves faster.In regards to your first point does direction of relative away/towards have any bearing
I meant reverse. We're talking about a coordinate effect, and one can create a non-inertial coordinate system where some clocks run backwards. Look up the Andromeda 'paradox' as an illustration of this.Quote from: HalcThe coordinate rate of clocks can indeed be negative given a non-inertial coordinate system.are you stating rate of atomic clocks as negative as going in reverse or just slowing down ?.
Because if negative = reverse
are we not setting the scenario of the paint analogy going from peeling/flaking into the wind to. returning to the painted surface becoming shiny and new then liquid in the brush/sprayer to been back in the paint tin ?If my coordinate system orders the paint events that way, then yes. It's just a coordinate system.
So is it not just an energy wave detector, detecting an effect from a cause ?
Then I would like to know average speed of all particles of the sphere(relatively of me).