billhinge

Yes I posted in the history section, the 456 page book is out next week (1st Sept)

In case anyone is interested the 'Apollo Remastered' 456 page book is released on 1st September from the usual places ...

https://www.bbc.co.uk/news/science-environment-62662685

I remember when I was at infant school in the late 60's you could collect the labels from spaghetti hoop tins (C&B I think?) and send them in to receive large poster size photographs of what I think may have been Apollo 8 or 10? Hoping they are in the book as I used to have those on my wall and was looking for reprints

8 minutes ago, cloudsweeper said:

The whole mass/energy/gravity/time thing is clearly very complex and non-intuitive.

For example, a Youtube video asserted that mass bends time, and bent time causes gravity.

None of it rests easy with me, but that is of course my failing.  I thought I understood what mass was, but even that is in question now.  

Good to hear all the contributions, though!

Doug.

gravity on the ISS is actually 89% of the surface gravity, it just appears to lack gravity due to free-fall .

We feel the moon's gravity and vice versa in tides

I think the problem is the mixing of newtonian and relativistic concepts of energy. In GR there is no clearly defined concept of potential energy . The previous question is then answered by the person lifting the weight gets hot through doing work

The problem with learning is the analogies we get taught initially  get engrained so it becomes difficult to shake. Took me ages to shake the newtonian model out of my head, same with covariant/contravariant vectors (at school you get taught euclidiean geometry and vectors look like A=5*i + 6*y + 7*z etc and the basis vectors i, j, k are at right angles to each other) and they don't even mention tensors other than pretend they are funny matrices

'A Youtube video asserted that mass bends time, and bent time causes gravity.'  Thats a good one isn't it , think its semantics 😉 - causes gravity? or causes to fall etc ? 

5 hours ago, PeterW said:

… got to keep Occam’s razor nice and sharp…

 

Peter

Always hated that expression, by whose definition do we choose? 

Did you dismantle the corrector ?

If you want to do it yourself you can buy the Hotech laser  https://www.firstlightoptics.com/hotech-collimation-tools/hotech-advanced-ct-laser-collimator.html  bit expensive now at £450 which you may wish to compare vs price of professional service, postage and insurance

You need a steady surface and mount plus about 3m of dark space (and a second tripod for the laser)

56 minutes ago, Macavity said:

I honestly wish I hadn't started the thead. lol. I (genuinely) congratulate you re. the
"super-determinism" bit though! Without Wikipedia I would have no idea! lol. 😉

I suppose I was intrigued to learn WHY she *so often* cites "Particle Physicists" as
the "bad guys" in this. I suppose I wondered how this had originated. I see Fifteen
years ago, she just seemed to be posting this stuff as not unreasonable questions.
You do have to wade through a lot of playground name-calling... on ALL sides. 🙄

I wryly admire her energies though. To opine on R-word, P-word, Gender/Sex, the
future of pro sport (Not a lot?) English/USA pronunciation and... *everything*!? lol
But thee is now quite a LOT of reward in being "controversial" (or appearing so)!

Aside: I not sure that being a Particle Physicist is JUST a privilege though! ISTR a
modest amounts of work are involved - Both getting there and working therein?
I am NOT convinced it's obligatory for everyone / anyone who gets *criticised*
by "science popularisers" to appear on some "Channel" to defend themselves!
Witten... various Laboratory Directors, "Chief Scientists"... "Bill Gates" etc. etc. 😅

It was her debunking of the delayed quantum eraser which was the clue, I wanted to know what her beef was and why some comment accused her of misinformation so did some googling 😉 

Notice how she states her assertions are universally accepted interpretations. Another clue was her apparent idolising of that guy again who was famously anti QM

Even in GR land there are disputes over why apples fall under gravity

Is an apple falling under gravity caused by time dilation at the earths surface or is the earth accelerating up to hit a falling apple? (or are  people using the wrong language) go ponder 🙂 

Recall the 2017 Jim Al-Khalili BBC documentary (free on amazon prime) in the last 5 mins at 1:22 when he quotes Kip Thorne saying matter moves to where it ages slower .

(sorry the documentary is called 'The Amazing World of Gravity' in case you want to watch it)

7 hours ago, Macavity said:

In retrospect, I'm just OLD? lol. The "Methods of Science" have changed? These days we
can circumvent *Peer Review* and "Speak directly to OUR Public"! lol. Sabine is a pretty
good singer too? (Thanks to my Youtube "Research", I have No Escape from her Music!) 🥳

"Music Critic": "Hey, Pretty Good... But you hit a couple of wrong notes"?
Sabine: WHICH (Vitch) two notes?!?
"Music Critic": "Uhm, not being specific" - "You're not a trained singer"...
Sabine: Then your post is stupid... I cannot improve... it is of no use to me etc. lol.

Welcome to the modern world of Science Popularising?
I have doubtless MISQUOTED some of the above!
I hope she doesn't get VIND of it! 😈

"Be Excellent to each other"? - Bill & Ted 😎
 

You seem to have a thing about Sabine 😉 , I'm not saying I agree with everything she says  and I know a lot of what she implies as fact is based on her belief in her super-determinism but she also says a lot that people can relate to and IMHO I enjoy the directness of many of her videos (everyone is selling something and she is a good sales person)

The issues here are not necessarily science/academia but human nature. Whenever you get tribes of people, even in industry it is difficult to get traction if your 'idea' doesn't fit the 'plan'. I've lost count of the number of crap projects that trundle on because of sunk costs, loss of face etc. (Fortunately I have/had jobs which allow me to call them out)

My view is that if you are confident in your product you can defend it adequately, if you can't then you don't have as good of a product as you think.

If mainstream physics don't like Sabine's social media then perhaps they should have their own social media outlet. Working in particle physics is a privilege that not many have, so maybe Ed Whitten should be telling  the public why tax payers should be paying their taxes to support his ideas if they are so great. Not being open gives the impression that something on the inside stinks and the tribe would like to keep it private. The taxpayer may ask why am I paying to support this esoteric research and shouldn't the money be better spent on NHS, climate change, etc (pick your  own good cause)

Having said that I don't begrudge funding physics through my tax £ but others may

52 minutes ago, iantaylor2uk said:

 

This is why some researchers are trying to "build up" space time from simple rules (e.g. Wolfram's cellular automata approach, or the approach used by loop quantum gravity theorists). 

Worth a read is Shell Beach https://jespergrimstrup.org/blog/

A third unfunded contender for a theory of everything behind String theory and LQG is Quantum Holonomy, and it is hated by both groups if you read the book, even if it shares some aspects of LQG dna (its the wrong kind of math), the author seems to say that research is very tribal.

It appears to be maintained by a team of 2 who struggle to get traction with mainstream physics. I don't know if its correct, but it is a compelling 'start from the bottom' with no assumptions approach and claims to show gravity is NOT quantum in nature and the standard model can be derived from first principles (and black holes have no singularities)

I posted 15kg of weights (3) wrapped in bubble wrap in a shoe box wrapped with T-Rex tape, thankfully it arrived intact, hopefully no one dropped it on their foot!

As an alternative view I guess it depends on what you want to do, do you want a qualification and letters or understand a subject mathematically in more depth and your starting point. I'm assuming a reasonable amount of physics and maths knowledge is assumed if you are mentioning M.Sc's

I was lucky enough to get a degree in astrophysics when they were free so I learnt physics & math techniques (mostly forgotten), but the thing I disliked was the focus on the 'how to derive an equation and put numbers in and turn the handle' rather than why, how does that work in relation to observed physics? e.g What does a path integral mean  anyway and why use that rather than another integral.

In those days there was no internet and the only source of info was the library or lectures, now we have great info online and arguably better presenters of information. 

Recently I went down the route pondering should I go for another degree but then I remembered, some subjects were boring (or at least the tutor was) and I focused on those subjects I liked

In the end I went the DIY route to teach myself (which is straightforward enough if you do maths revision etc, even after 40 years its funny what you can remember. In someways it's easier to understand than when you are 20 with loads of stuff going on). At the moment I think I have a reasonable mathematical  understanding of Riemannian geometry,  Christoffel Symbols and Schwarzchild metrics  and how to apply them, better than my 3rd year understanding of GR anyway. The fact that there are no deadlines, exams, time pressures  makes life easier I find.

(Also doing Quantum Field Theory, not the old particle in a box stuff- my uni professor never did answer my question as to why you don't use Schrodinger hydrogen perturbation theory for helium atoms, so what do you do instead, why use Hamiltonians vs Lagrangians etc 😉 )

I'm nearing retirement so no aspirations job wise and I'm doing it for my own interest

27 minutes ago, DaveL59 said:

hehe yeah technical indicators, support and resistance levels and so on, learned some of that when I dabbled with forex trading and writing my own bots. Thing is they rely on a behaviour within a sort of norm that doesn't really exist and is influenced by external events that can blow those away. Factoring in those events and their effect tho isn't trivial and typically needs some human interpolation based on experience and hunches. Easier to write a system to try ride a trend than to make quick coin on short fast moves but needs deep pockets to ride the waves along the way.

Maybe, but the point I was making was that it is possible to use computational tools to see what are the key factors that an AI learnt and by what percentage each factor matters

It's not a leap of faith to me to use the above analogy with physical models and parameters. Problem I see is that if we try to understand gravity, would it learn Newton or Einstein or GR hybrids if we teach it with a falling apple vs satellite vs black hole? The AI's conclusions would be influenced by its observations and accuracy (and experimenter's bias) surely - as would ours? 

On 31/07/2022 at 22:57, Macavity said:

Maybe we're not that into "talking computers"! But: Can "AI" discover new Physics? 🤔
For a change not the Youtube link! (But there is a FUN video embedded!)
https://www.creativemachineslab.com/hidden-variables.html
Interesting stuff, if you're into Robotics? 🥳

Sounds pretty cool to me, there were similar projects for financial markets. If you believe in technical analysis, which TA indicators are were more significant impacts on price . eg https://deepai.org/publication/bayesian-regression-and-bitcoin

If you are familiar with AI and github its fairly easy to try yourself

When I was a first year undergraduate one of the first questions discussed in tutorials was working out factors that influence a system and how they are proportional to the result. Sounds like an AI version of that

Lots of food for thought

36 minutes ago, robin_astro said:

Hi Steve,

No need to patronise me. I am a career hardened  physicist happily living in a quantum mechanical and relativistic universe  😉  

The equipment is just an off the shelf astronomical spectrograph and my measurements were just to test its mechanical stability under different orientations, not to make some profound physical insight. I saw this thread and saw the measurements as an interesting  alternative perspective on the measurement of the speed of light which does not have the difficulties of  round trips or synchronised clocks covered in the article and videos, though it may have other difficulties which we are exploring here (It is clearly a fully one way measurement, no reflection, no return path. The light leaves one end and arrives at the other where the wavelength is measured from the diffraction pattern after being dispersed by the transmission grating. I don't understand why you are still disputing that). 

 According to the measurements, multiplying two independent locally measurable physical properties of electromagnetic radiation, frequency and wavelength gives a constant value, v which  is independent of the orientation.  (The experiment could be made more robust by actually measuring both wavelength and frequency at both ends of the leg rather than assuming the frequency is unchanged. Although this would need two clocks, importantly there is no requirement for them to be synchronised as in the time of flight measurement, just for them to run at the same rate which would be the case for two clocks at rest relative to each other as here, according to special relativity ) 

You offer QED as an explanation as to why this value v may not be the velocity of light and which might be constant even in the case of a universe where the speed of light is different dependent on the direction of travel of the light beam but I have only seen generalisations so far. (The quantum effect of the observer on the measurement and the properties of the grating are spurious here. I don't understand why you would introduce these except to muddy the waters)

I fully expect there is some reason it would give the same result even in a universe where the speed of light is directional  but as an experimental physicist I have the luxury of saying "here are my measurements, explain them 🙂"

Cheers

Robin

 

 

How am I patronising you? I don't know your qualifications

I'm just trying to be civil and clear and I'm not just writing to you personally but to all the other readers of this thread 

I thought I was clear,  a spectrogram is a special mirror therefore it fails the test of direct measurement since your system source, mirror, detector.,the same as a traditional 2 direction measurement of light. QED describes the spectrogram part and why you are not measuring a direct A->B measurement

Anyway I've said what I intended, so best call it a day

21 hours ago, robin_astro said:

 

Sorry if I implied this, it was not my intention.  I invited you to demonstrate how a universe where the speed of light depends on the direction of measurement could be compatible with the results of my experiment which appears to suggest that either the speed of light is not direction dependent or as Andrew proposed, space is anisotropic (so the distance between two  objects stationary relative to each other depends on the direction of measurement).  Either viewpoint may be valid as Andrew proposed but personally I would then apply Occam's razor and chose  the simplest solution which is space is isotropic and the speed of light is not direction dependent)

The arguments put forward in the videos in the thread to support the impossibility of measuring c using one way time of flight measurements do not involve quantum mechanics. (Once we introduce quantum effects all bets are off 😉) They revolve around the impossibility of two observers agreeing on a common time, (which is correct and a consequence of relativity) and hence assert that any experiment to measure the speed of light must involve a round trip leading to the conclusion that the speed in each direction cannot be independently determined.  There is an important difference however between my experiment and one and two way time of flight measurements. My method uses one clock (The frequency of the light) and a unidirectional light beam (lamp, transmission diffraction grating, camera rigidly mounted in line, a fixed distance apart)

You can see the apparatus I use (an astronomical grism spectrograph with a built in calibration lamp) here 

https://www.shelyak.com/wp-content/uploads/Alpy600Demetra-510x320.png

The question I pose is why would this measure the same wavelength of the light independent of the direction it is pointing in if the speed of light is direction dependent ?

Cheers

Robin

Thank you, nice website! Let's go back to the beginning. The article states

'The speed of light is an assumption, not a certainty. It’s an assumption in that we have never experimentally measured the one-way speed of light. '

I responded to say, yes, in fact its baked into Einsteins original paper! (I also posted a video that discusses this, the fact that QED, not just Quantum Theory but Quantum Field Theory is not mentioned is not relevant as we were just talking about the challenge of directly measuring A to B vs B to A )

Most reasonable people would agree that the universe is isotropic (you quote Occam's razor which is a reasonable response), but the issue is do you accept that it is isotropic based on faith or do you try to prove it?

The article and my response asserts that the speed of light in one direction can't be measured directly measured.

No one disputes that you can calculate 'a value' from  an equation which includes fundamental parameters but it doesn't demonstrate experimental measurement of the one way speed of light

Your counter-argument seems to be that you have devised an experiment to measure the one way speed of light

My response was, you haven't since you have used a diffraction grating which is just a specialised mirror - these effects are fully described by QED (see 'The strange theory of light and matter' by Feynman)

True, using QED to explain diffraction, reflection and other effects involving light interacting with matter is using a sledge hammer to crack a nut, but Huygens etc are just analogies that give the same results in a way you use Newtonian mechanics rather than general relativity geodesics to describe earthly motion of projectiles. But don't mistake Huygens and Newton for reality. When you know that light is being affected by matter you need to understand mirrors are quantum mechanical in reality! (interestingly QED explains why your telescope secondary doesn't block the star in the centre of your field of view or why holes don't leave gaps in your telescope image - go read reddit or cloudy-nights if you want a laugh at the hand waving arguments). Since we are really in the realm of QED, we know any measurement affects the original state.

So to summarise, your use of a specialised mirror means you haven't measured the 'one-way speed of light. '. I don't dispute the accuracy of your measurements and what you have created with your website etc is highly commendable. Strictly speaking since diffraction gratings are made of atoms you should also try gratings of different materials to see if there is any effect there

I'm sure I won't convince you but it may convince some to dig into this subject further,  🙂 (the feynman book is cheap and part text chapters, part maths, path integrals, probabilities and Feynman diagrams and there are some semi technical videos on the subject)

cheers 

steve

4 hours ago, robin_astro said:

No I am not. The original hypothesis at the top of the thread  was that it was impossible to measure the speed of light in any one direction. My method (looking for any change in the diffraction pattern produced by a beam of photons sent in different directions) just uses a clock (the frequency of the photon generated by a transition of an electron between two energy levels in an atom),  a yardstick and geometry.  The only formula is v=lamda*f   which identical to that used to calculate the velocity in the return trip experiment (v = 2d/t) except in my experiment the beam is only sent one way. If the velocity of light was direction dependent the wavelength (as measured in the diffraction pattern) would be different. It is not, therefore the conclusion is that either the speed of light is independent of direction,  or  space is not isotropic such that the measurement of distance is in some way directional, (and in some peculiar way, since the diffraction pattern is produced orthogonal to the direction of the light beam)  You are welcome to formulate such an alternative universe and propose how it may be tested.

Cheers

Robin

You are using a 'diffraction grating', which is essentially the same as a mirror at the atomic level. ie photon scattering by atoms hence not a one way trip - refer to Feynman QED, you have chosen to adopt a classic approach which still gives the same answer (nothing wrong with that)

Indeed the photon being diffracted and measured is not even the original one being emitted. 

How does your method differ from the MM expt which also uses mirrors?

I don't say the speed of light 'isn't' isotropic so why do you assert I'm a believer of  alternative universes and physics? Proof and belief in assumption/axioms are subtly different

you are missing the point, sure you can calculate a value for c from other formula such as Maxwells eqns  etc but the question was about measuring directly using distance and time

- refer to Einstein

I can (and most others do) measure the square mass of a neutrino to be a negative number but we choose to say the error on the calculation is just enough to to make it a small positive number and hence not an imaginary mass when square roots are taken. This was my final year grad project study on radioactive decay many years ago, neutrino mass being an easily calculated by product based on conservation of momentum. But it wasn't a direct neutrino mass calculation.

On 18/01/2021 at 21:31, Ouroboros said:

Eh?  How have I not heard of this before?  I came across this today in the article linked below. 

“The speed of light is an assumption, not a certainty. It’s an assumption in that we have never experimentally measured the one-way speed of light. The best we have been able to do, even with our most sophisticated modern technology, is measure the roundtrip speed of light and assume that the speed is the same in both directions.”

We don’t really know the speed of light.

I would be interested to read people’s comments. 

Hi

The issue is as follows, Einsteins original paper states this is  an assumption (by definition) !

'We have not defined a common “time” for A and B, for the latter cannot be defined at all unless we establish by definition that the “time” required by light to travel from A to B equals the “time” it requires to travel from B to A. '

https://www.physics.umd.edu/courses/Phys606/spring_2011/einstein_electrodynamics_of_moving_bodies.pdf (page 3 top para)

I don't think many dispute or believe c is different in different directions, but it's there in black and white, you can't prove it, you assume it. You always need a two way trip, even MM relies on mirrors

There is a good Veritasium on this 

Thanks both, so the choice is  a seam or zits?  😂 I'm happy with how it turned out but I may try printing again in carbon fibre PLA as I want to teak a couple of tweaks to strengthen the OTA join - only held by 3 small bolts! Cheaper than paying £200+ for a custom metal jobbie

I had planned to sand and paint anyway but I was just curious (I'm using Qidiprint which is a Cura clone, its updated fairly regularly and usually does a good job so haven't bothered copying all the settings across to Cura)   

I may use the remains of this roll of PLA on v2 of my cycloid gearbox, measurements weren't quite right last time, couldn't get internal wheel to fit properly with the dowels

I used this blueprint https://www.ewhiteowls.com/2022/02/the-ultimate-guide-to-design-cycloidal-drives-the-beating-heart-of-robotic-arms/ for the cycloid

On 19/07/2022 at 17:20, billhinge said:

Step 1 complete

Measured inside/outside of TMB LZOS 115 Kruppax  tube and outside of new APM 3.7" R&P focuser (to replace existing 2" Feathertouch) accurate to 0.01 mm - got close with a micrometer and kept increasing size by few hundredths till I got a tight fit. No one makes an adapter this size and it would cost a fortune for a custom job so DIY is best

Final Prototype 'rings' now correctly measured and fitted snuggly against OTA tube and focuser - holes all line up

Needs to support either Riccardo flattener etc so now to design the bit between the tube end and the focuser and make a bit thicker

This is printed in  thick PLA which I plan to flock with protostar and paint (got some Mosou Black to try - good excuse 😉 )

Also printed a cycloid gear box but measurements are out slightly, needs tweaking and reprinting 

printer is Qidi X-Max

PLA seems quite rigid 

 

 

I printed the full adapter but given the heavy weight of a 3.7" focuser, Riccardi flattener and other kit such as cameras, is straight plain PLA tough enough.

I have carbon fibre PLA as well just in case, or could do nylon if required. The PLA does seem very rigid, I can't bend it by hand, walls are about 6mm thick.

Any idea what causes the straight ridge on second image, it isn't in the model?

The adapter slides over the focuser and into the OTA tube

Step 1 complete

Measured inside/outside of TMB LZOS 115 Kruppax  tube and outside of new APM 3.7" R&P focuser (to replace existing 2" Feathertouch) accurate to 0.01 mm - got close with a micrometer and kept increasing size by few hundredths till I got a tight fit. No one makes an adapter this size and it would cost a fortune for a custom job so DIY is best

Final Prototype 'rings' now correctly measured and fitted snuggly against OTA tube and focuser - holes all line up

Needs to support either Riccardo flattener etc so now to design the bit between the tube end and the focuser and make a bit thicker

This is printed in  thick PLA which I plan to flock with protostar and paint (got some Mosou Black to try - good excuse 😉 )

Also printed a cycloid gear box but measurements are out slightly, needs tweaking and reprinting 

printer is Qidi X-Max

PLA seems quite rigid 

Here is a link to a site showing Hubble vs Webb

https://bigthink.com/starts-with-a-bang/universe-before-jwst/

2 minutes ago, Zermelo said:

Yes, I prefer that look to the oranges of the test images. It will be interesting to find out how they assigned the colour.

I expect it will be more impressive with a bit more scientific commentary.

NASA’s James Webb Space Telescope has produced the deepest and sharpest infrared image of the distant universe to date. Known as Webb’s First Deep Field, this image of galaxy cluster SMACS 0723 is overflowing with detail.

Thousands of galaxies – including the faintest objects ever observed in the infrared – have appeared in Webb’s view for the first time. This slice of the vast universe covers a patch of sky approximately the size of a grain of sand held at arm’s length by someone on the ground.

This deep field, taken by Webb’s Near-Infrared Camera (NIRCam), is a composite made from images at different wavelengths, totaling 12.5 hours – achieving depths at infrared wavelengths beyond the Hubble Space Telescope’s deepest fields, which took weeks.

The image shows the galaxy cluster SMACS 0723 as it appeared 4.6 billion years ago. The combined mass of this galaxy cluster acts as a gravitational lens, magnifying much more distant galaxies behind it. Webb’s NIRCam has brought those distant galaxies into sharp focus – they have tiny, faint structures that have never been seen before, including star clusters and diffuse features. Researchers will soon begin to learn more about the galaxies’ masses, ages, histories, and compositions, as Webb seeks the earliest galaxies in the universe.

This image is among the telescope’s first-full color images. The full suite will be released Tuesday, July 12, beginning at 10:30 a.m. EDT, during a live NASA TV broadcast. Learn more about how to watch.

https://www.nasa.gov/image-feature/goddard/2022/nasa-s-webb-delivers-deepest-infrared-image-of-universe-yet

If you want to be OTT and tinker more, you could choose ABEC 7 grade bearings https://www.skf.com/us/products/mrc/precision-abec-5-and-abec-7-bearings Some skateboarders swear by them (I'm not a skateboarder), lots of ABEC7  skateboard videos on youtube. Its up to you whether you 'believe' or not

The worm bearings are easy to find but the big bearings can be £80 each !

I would be tempted to try https://www.ebay.co.uk/itm/193592991803?hash=item2d130aa03b:g:DOIAAOSw0SxfGtat&amdata=enc%3AAQAHAAAA4M4fESIOVpM4AfPZgMpi5H5QYHh3mNPYPNNE%2BqD506Sb3HBbCJq2MTwHaMA%2B1ZgcsvUW%2F%2B%2FCVMj%2FaV6RWMZnlz8bjAc%2BF4LweN18YDfkyoAUG3oTb%2F9Kh6IsfLJuwZWnXKiVnVvnbqMx8JQvMVztBSntSyikkAw%2FUMF3IWKp%2FrODLTpJ6GdCbnyeD%2Fn56xgMbN44%2Bz%2B2zNw4nWeTWeXurvWRCwbrm22ZscttQJhfKFMvGs69HYqSi3SyRlXG%2FmjeL9WFn9G1IKNxHerZBTKUjvawc1bEcsFEYJk34MfH7zjp|tkp%3ABFBM7sbGobJg. if I didn't have the 100% pure stuff both grease and dry powder bought from the US some years ago. You can even put it on teflon to make it slippier!

Or you could go all in for powder coating and run everything dry https://www.ws2.co.uk/

On 15/05/2022 at 21:44, Deadlake said:

That’s a good question, I do not know.

Rumoured price is around $3000.

This is close to RST-300 in load capacity, 20 kg, so why not two scopes?

Price on two well known UK sites is now £2450 which seems very reasonable