andrew s

I have started up loading my data into the AAVSO exoplanet database where NASA imports the data into its Exoplanet Watch database. I had not realised this until I discovered my data there. They analyse the data and if they deem it ok use it to update the planets emphasises. My data is the last point on the right.

Regards Andrew 

2 minutes ago, saac said:

At that moment of realising would we just disappear in a puff of blue smoke. 

Jim 

I think therefore I'm not. 🤐

Regards Andrew 

I think we must have a common or at least very similar perception in that our mental models of the world are congruent.  If not then how do we communicate and create our rich culture and technology. 

When misaligned we identify mental illnesses and pathological behaviour. 

What astonishes me is our lack of access, via introspection,  to our metal processes. Maybe it has to be like that for our sanity. 

Regards Andrew 

19 minutes ago, saac said:

I think that must be where I left my car keys  

Jim 

I think it more likely it's where all socks were initially paired up correctly - before they became fermions. 

Regards Andrew 

The other standard time quote is "time is what stops everything happening at once". The root of time is in the observation that things change.

Anyway enough of this pop philosophy back to science.

I have found this paper here which discusses the changes in wavelength associated with Plank scale quantisation as @saac and @vlaiv proposed.

While this one discusses the impact on X-ray and gamma-ray wavefronts.

Both put tight constraints on any proposed foam.

I did find a Sky and Telescope article claiming a detected difference in arrival of soft and hard gamma ray arrival times. However,  it was so full of pop science nonsense I could not bring myself to link to it. Further,  I could not find a related paper. If indeed it was a robust result the researchers would be up for a Nobel prize.

Regards Andrew 

3 minutes ago, iantaylor2uk said:

If space is quantized it will be at the Plank scale, which is many orders of magnitude lower than anything we can measure at the moment. I think it is quite likely that space-time is quantized as I don't think infinity has any place in physics (infinity is a mathematical concept not a physical one). The fact that continuity breaks down at  the lowest length scales also means we will end up with difference equations rather than differential equations. 

While I can't put Google on the paper but it has been tested to below the Plank scale. 

If space were quantised different wavelengths of light would travel at slightly different speeds and this would show up in the arrival time of light of different wavelengths from transient event at astronomical distances none was found.

I will look again tomorrow. 

Regards Andrew 

As far as I am aware there is no experimental evidence that either space or time are quantised. Both QFT and GR, our two most successful theories, are both based on a continuous spacetime. It certainly has been looked for.

I am with Einstein that time is what clocks measure and space is what metre sticks measure.  A pragmatic operational approach that I am sure @saac will appreciate.

I have half a book case full of books about "time" accumulated over 60 yrs of pondering about the nature of time but none has been as insightful as Einstein's  position. 

There is a serious approach to time not flowing in the Block Universe where everything exists as a 4D block of all space and all time. In this Universe we just perceive time flowing as we trace out a trajectory.  Interestingly,  it's advocates claim it solves the fine tuning issue but this is challenged by others. I  have one or two books on that too😊.

Regards Andrew 

Just now, ollypenrice said:

There's the rub. I have always struggled with the anthropic principle, not because I don't understand it but because I don't see the need for it. It seems to me (perhaps wrongly) that it is born of a spurious need to account for something which 'just is.'

Olly

I agree. It has several  versions of varying degree. I feel at best it is circular and worse empty. I am not aware of any new predictions of substance from it.

Regards Andrew 

Of course once something has happened ths odds of it happening are 100% .

Regards Andrew 

1 minute ago, ollypenrice said:

They do, I agree, but so do the parameters applying to my knocking the vase off the table if I look back through the accident expecting those particular fragments to be created.  The outcome of the falling vase has incredibly specific consequences - say, one thousand three hundred and forty one fragments of shapes x, mass y. It takes very specific initial conditions to produce them, yet they were formed without any fine tuning. We simply accept that those were the fragments produced. So why do we have trouble accepting that the big bang happened to produce what it did?

Olly

Also, consider the unimaginable odds against you and the vase being created and in such proximity that you could knock it over!

Regards Andrew 

As @iantaylor2uk mentioned one escape is a more or less strong version of the anthropic principle. 

Another is if they were different maybe a totally different set of entities may have evolved one we can't or have not conceived of. Normally the discussion goes along the lines that if the fine structure constant had not been X +/- a small bit atoms would not be stable. However, we don't consider if other elementary structures could be as we have no data on which to speculate on.

Regards Andrew 

Have a look at this posted earlier 

Regards Andrew 

43 minutes ago, EarthLife said:

As light is affected/bent by gravity, then the speed of a photon moving away from the center of gravity (say the Earth) will be different to the speed of a photon moving directly towards the center of gravity - one way that the speed in each direction can be asymmetric.

Gravity bends spacetime. Light follows the "shortest" path which are straight lines when there is flat spacetime and curved lines (geodesics) when spacetime is curved as in GR by mass/energy. 

Regards Andrew 

40 minutes ago, EarthLife said:

As light is affected/bent by gravity, then the speed of a photon moving away from the center of gravity (say the Earth) will be different to the speed of a photon moving directly towards the center of gravity - one way that the speed in each direction can be asymmetric.

If you measure the speed of light locally in a gravitational potential well you will get c. What changes is the frequency the light will be red shifted climbing out of the gravitational potential well and blue shifted falling in.

Regards Andrew 

1 minute ago, saac said:

That was my initial thoughts Ian but I think what the issue is with that is that it represents a "derived" value, assumption are in effect baked in. The question arises from the possibility that space may not be isotropic in nature with respect to the passage of light.  So the challenge for the experimentalist is to find a way to verify the one way light path and it seems impossible. 

Jim 

Just to be clear you can measure the anisotropy without trying to measure the one way speed. This has a tradition going back to the MM attempts to detect the eather. 

Regards Andrew 

40 minutes ago, saac said:

Relativity effects of time dilation, length contraction etc are predicated on Einstein's postulates (Galilean invariance holding true and speed of light being fixed).  If the speed of light was dependant upon direction would that not show in our measurements of relativity effects?  Or is the magnitude of the speed less important than light being compelled to travel at its maximum speed whatever that would be in either direction?  

Jim 

The isotropy of the speed of light is built into SR through the Einstein synchronisation procedure. It's not the only possible procedure and you can develop a nonstandard relativity based on them. However,  while the equations are more complex you get the same predictions as SR.

As the paper I linked to show the measured limits of any anisotropy are very tight.

In my view and that of the SI board it's a done deal and the isotropy is built into the SI standards.

Regards Andrew 

44 minutes ago, iantaylor2uk said:

I don't know what you think the physical basis is for why the speed of light would differ in direction.

If you look at Maxwell's equations, there is a single speed c, predicted for electromagnetic waves, and as far as I'm aware the c that appears in those equations does not depend on direction, and electromagnetism agrees well with experiment. 

In addition, there have been many published papers where general relativity has been applied to pairs of spinning black holes, particularly for black hole collisions, where as I understand it the simulations agree well with the measured data. 

I think if the speed of light were different on the two separate paths application of GR to spinning systems would have shown up as discrepancies with experiment. 

You can have an eletrodynamics with an anisotropic speed of light but the equations are much more complex. 

The consensus is that you can measure the anisotropy but not the one way speed.

This Wiki article is a good starting point 

https://en.m.wikipedia.org/wiki/One-way_speed_of_light

Regards Andrew 

PS This paper https://arxiv.org/abs/1011.1318  reviews the isotropy of the speed of light see table 5. Current experiments show it is isotropic at the 1 in 10^-10 level.

19 minutes ago, EarthLife said:

Both clocks start continuously TX'ing their pulses.

Clock 2 then phase locks their TX pulse to the RX'ed pulse from clock 1.
ie, clock 2 synchronizes it's TX pulse with the pulse it RX's from clock 1.

If the speed of light is actually the same in both directions, clock 1 should RX the pulse from clock 2 at the exact same time it TX's it's own pulse.
If clock 1 see's a difference in the two pulses (TX'ed pulse and RX'ed pulse), then the speed of light is different between the directions.

Yes ?

You need to be clear what your trying to measure.  One way speed requires the clocks to be synchronized  anisotropy of the speed does not. Regards Andrew 

To honour the original I would propose it has to be a man made mechanical device that operates (I.e. has moving parts) continuously without any energy input.

Regards Andrew 

PS this seems close https://en.m.wikipedia.org/wiki/Beverly_Clock

Not been wound since 1864. However  it uses changes in air temperature and pressure as energy input so does not really count.

Light going around any closed loop in space has to go in both directions so it won't measure the one way speed of light.

Formally, the claim is about the local speed of light. Things get very complex in curved spacetime where you can't uniquely add vectors (like velocity). 

As an example consider two cars on the equator on opposite sides of the globe both heading north at 10mph.

What is there relative speed? You calculate this by bring their velocity vectors together via a process called parallel transport.

Well if you parallel transport them round the equator they are equal so relative velocity is 0 mph.

However,  if you parallel transport them along a great circle throuh them and the poles they are travelling in opposite directions so their relative velocity is 20 mph. 

Fun isn't it 

Regards Andrew 

Have you checked that the power to the 460ex is clean both via USB and power?

Noisy DC could play havoc with the chip.

Regards Andrew 

30 minutes ago, markse68 said:

Hi Andrew, was it a desiccant dehumidifier? I understand that they’re better at low temp than the refrigerant variety but having bought a second hand one, taking it apart and discovering scorched, melted plastic parts inside, they do kind of scare me!

Mark 

Refrigerant type. It many years ago now. Regards Andrew 

18 minutes ago, CraigT82 said:

If you don’t mind me asking, what was the cause of the fire? Perhaps a learning point for the rest of us? 

I was about to go on holiday and the only item powered up was a dehumidifier.  The fire was so hot everything was melted or mangled apart from the steel pilar. 

So I can't be absolutely sure but it seems it was the dehumidifier. 

Regards Andrew 

Well this did happen to me. My observatory burnt to the ground. Luckily, my house insurance paid out.

The up shot was I got a better setup as rather than incrementally adding and changing things I could get a balanced setup in one go.

Regards Andrew 

33 minutes ago, CraigT82 said:

I see there is an integrated adaptive optics module that can be purchased as an add on to the PW1000 system too. Would be a rude not to.

https://planewave.com/commercial-pre-integrated-adaptive-optics/

I love that the video has a cheap ASI camera rather than an up market 40k sCMOS camera.