saac

Just now, Greggy-spaceboy said:

Yeah I think that is a valid point as it would be perhaps more likely to be environmental .... although the frequency of external bodies hitting the earth carrying microbes that can survive the space journey might be plausable too... either way it could of been possible on both fronts and as we know , it had to on some fronts as we have arrived

Absolutely  

Jim 

It really is a great and fun question.   

1 minute ago, Greggy-spaceboy said:

i believe single cell organisms evolved into multi-cell they believe due to a predator ... that predator would perhaps not of existed on the planet before but perhaps came from external meteorites that crashed on the earth, started to gobble the single cells , which provoked them to evolve.  Once that happened complex life happened really quickly , (500million years to get to us) .. i felt it is an important point perhaps if somehow we could look at earth's relative positiion in the universe and look at areas that are "a similar age"

I haven't came across the "external predator" theory before but I guess that evolutionary pressures are inevitable as they would arise from any "stress point" . A stress point being a condition which places a challenge to the organism, environmental change being the most likely.  Stress in turn would give rise to natural selection processes which would favour organisms with advantageous mutations.  So I'm guessing, again I'm not on solid ground here,  that evolution could occur without an externally arrived predator to light the blue touch paper.  Homegrown (evolved) predators would of course in turn eventually bring additional stress points and perhaps accelerate the natural selection process. 

Jim

For what it's worth I think the question was an interesting one , and I don't know why but I'd never really considered it before !   Ask the same question of a sterile Earth with all the necessary precursors - would there be a necessary time line threshold before life could arise.  Surely not, surely if it is a random and inevitable occurrence it is just  probability and luck of the right molecules being present in the right conditions.  Or am I missing something fundamental?

Jim 

Greggy-spaceboy to answer your question directly  "do exoplanet hunters factor in their searches a filter of an evolutionary timeline" then I suspect the answer is no.  I may be wrong but I think they simply look for the signature affects of an orbiting planet on its parent star (radial velocity and light curve dip) . Once they detect a candidate star it is then a matter of looking at size of the planet and its distance to the star to consider whether it resides in the habitable zone.  To be honest I've not really considered the necessity for an time bar threshold for life. By my way of thinking , if life is a natural and inevitable consequence of the characteristics of our universe then surely the only precursor is the conditions - stars and the chemistry.  I suppose then the only time bar would then preclude life emerging in the timeline of first generation stars - organic building blocks not yet created and scattered across space !  Im not really sure about that last part but that is my thinking anyway.  

Jim 

23 hours ago, Michael Kieth Adams said:

The more distance away from us something is, the faster it moves away from us.    Things are moving slower near to us.  Am I wrong to believe that the huge speeds we see happened long ago and the fact that things near us are slower has to mean that things are slowing down.  Closer is more recent, far away is long ago.  Do I misunderstand ?

I don't believe that this is a correct interpretation . The speed to which you are referring is, as described above, a consequence of the expansion of the space that the objects inhabit.  The expansion of our local space, the space we inhabit and share with our galactic neighbours,  does not dominate rather gravity is the more dominant influence.  So nearer things are not slowing down compared to more distant (earlier) objects they simply inhabit a different space which in turn imparts the "local" expansion signature onto those objects which we observe in red-shift.  The more distant objects carry the signature of their "more distant" expansion of space, again in the form of red shift,  and they inhabit space at a steeper part of the expansion curve.  Remember also that it is space and not the objects therein that is expanding.  I think you are right to assume though that the oldest objects in our universe are furthest away from us .  Even that interpretation may even be fraught with difficulty as, as far as I understand it, it is not really possible to use a  notion of simultaneity across the expanse of the universe - the moment of "now" here on Earth does not translate to the same point in time at the other end of the universe !   My understanding here may be incorrect , happy to be educated, but I believe there is no fixed or absolute point of universal time. 

Jim

Good luck with it Lars - once you get the hang of it it can be very satisfying.  Have you tried Fusion 360, it's good but usual learning curve ?

Jim

Lol , I'll  try but don't go cashing any cheques on this   Dark energy is a candidate for causing what appears to be an acceleration in the rate of expansion.  The detail  has still to be written !  

Jim

I think what you are looking at is the expansion of the universe which gives rise to distant objects having a higher recessional velocity than nearby objects.  This is measured in the red shift of distant galaxies which is one of the supporting pieces of evidence to support the expansion of the universe.  My understanding is  that it doesn't point to things slowing down rather than the stretching of the space between the objects. 

Jim

First class effort and perseverance.  I'm hoping to get a few practice shots in this week weather permitting - still don't know if it will actually be visible much from here but I'd love to photograph them. 

Jim

On 08/12/2020 at 08:59, maw lod qan said:

Any idea where this is showing from?

In Fla Saturn is up at an angle to the left.

The pictures showing the track position is taken for British Isles.  If you have Stellarium you could forward the date to find the positions relative to the Florida sky.  I'll give it a go.  

Jim

PS - I think if I have done it right it should look like this at the moment - pretty close to each other already - this was for Bloomingdale Florida .  I don't know if that was of any help !

26 minutes ago, andrew s said:

 

Stop blaming the hammer it's your foot that is applying a proper acceleration (deceleration ) force to the hammer.

Regards Andrew

So many ways to think about what caused the pain - and there's me , just thinking about the pain. I'm missing out on so much of the experience 😜

Jim

2 minutes ago, vlaiv said:

Don't know why everyone keeps blaming gravity for this, when it clearly states that both hammer and feather fall with same acceleration.

Remember that next time you drop feather on your foot

I knew I was doing something wrong  vlaiv    Alexa - set reminder - "remember to replace lump hammers with ostrich feathers " 

Jim 

The next time I drop my lump hammer on my foot I shall console myself that the blistering pain  ringing through my very core is not the result of a force rather my foot preventing the hammer continuing on it' geodesic line of travel   I await the "happiest thoughts of my life"  moment as Einstein commented as the pain slowly subsides - it never comes  -  gravity remain a stubborn force!

It's a hard idea to shake , it's embedded in our experience, deeply rooted from childhood onward. Described in one of the books I'm reading, The Ascent Of Gravity by Marcus Chown,  " our only real and tangible everyday interaction with the fundamental forces" - electromagnetic competing equally one could argue but point taken . Only until the very senior stage of school physics at say A level, Adv Higher and the Int baccalaureate does GR feature in any meaningful way (still only introductory and very much qualitative ). Only then does the geometric nature of gravity reveal itself. So to the majority of school leavers and general public gravity remains the familiar force of the lump hammer dropped on a foot!  In the professional realm  engineers (my own background) have no need or care to see gravity other than the agent of force (weight)  as they strive to keep aircraft in the air and bridges standing.   The thing is, the force nature of gravity is not redundant and although not a complete description, depending upon the application at hand it is perfectly fitting. I'm not one hundred percent certain of this but I would be surprised if in any of the orbital mechanics mathematics of the Apollo programme reflected anything but Newtonian mechanics, where gravity prevailed as a force of attraction.  I guess much as we talk about the duality of light (particle and wave nature) we could play fast and loose and think about the duality of gravity - the model chosen to fit the application.   I bet the the cosmologists working on dark matter theories unlike us armchair warriors know exactly when it is appropriate to consider either nature of gravity though.  What I will say is that this forum  is a fantastic resource; I've certainly benefited from reading many of the really informed posts from contributors like Andrew S, Vlaiv, and Georges Jones to name only a few.  I often find I benefit from pre reading on here before trying to make sense of the more academic publications where the maths can be impenetrable.  This really is a great community in that respect. 

Regarding need for another quark - there was news of a new penta quark  last year, don't think it was necessarily hinting anything towards gravity/dark matter though though.   Now there is a thing - all school books need to be revised!

https://home.cern/news/news/physics/lhcb-experiment-discovers-new-pentaquark

Jim 

32 minutes ago, Viktiste said:

IIt just sounds like a fudge factor made up to fit nicely in the equations. I'm probably wrong though. 

No I can't tell you where the course of research should be, and if I did nobody would care anyway 😜

 

I think if it is a "fudge factor" then it is a so with a fair amount of weighted and reasoned argument behind it .  In any respect, surely  most of science has progressed  at some point on the basis of a fudge or assumption -  albeit educated ones.   Hasn't it (dark matter ) only really been put forward as a candidate for what may be causing the departure from predictions?  I don't see it as any different from say the work done by Peter Higgs who saw a gap in a pattern and theorized the existence of the Higgs field to fill that gap. The challenge was picked up by the experimentalists to search for it.  It turned out he was right but he may have been wrong and something else would have been found to be the cause of the gap.  Im sure the same process will play out with Dark Matter it will either be confirmed (if within our ability to detect ) or some other candidate will emerge.  Either way our understanding will progress.  If it is found to be a reality I do hope they rename the thing straight away  call it a negative expansion flux , index or accelerant or whatever  - too much woo woo connotations with dark matter and dark energy  

Other than the MOND posted up by Andrew I'm nowhere near knowledgeable on other current alternative dark matter  candidates but they will no doubt exist.  Would be good to hear what if any are gaining traction. 

Jim

5 minutes ago, JamesF said:

I'm sure this is not limited merely to physics.  But I bet it's quite often what has happened when you hear a scientist say: "Oh!  That's odd."

James

May be apocryphal but the story goes the discovery of the strange quark was exactly that   " that's strange "  

jim 

12 minutes ago, andrew s said:

While it does well with galaxy rotation (that's what it way aimed at) it does less well with clusters of galaxies and as the Wikipedia article notes it still needs dark matter to help it out in such cases. 

Regards Andrew 

It's intriguing in that respect. I can't think of any parallels of the top of my head but there must be other models in other areas of physics which only take us so far before breaking down (classical and quantum must be replete with examples).  I think it is  intuitive that the reach of a model must surely  be limited by the boundary conditions in which it was framed.  We run into problems then as our capability  allows for more accurate or rather greater resolution in our measurements then the more susceptible our models become to falling to the effects of unknowns.   I hope that makes sense - I think I know what Im talking about but I often confuse myself  

Jim 

13 hours ago, andrew s said:

Here the synopsis of a as yet peer reviewed paper on Modified Newtonian Dynamics. Posted on ArXiv.org where per published papers are collected.

The global stability of M33 in MOND

Indranil Banik (Bonn), Ingo Thies (Bonn), Graeme Candlish (Valparaiso), Benoit Famaey (Strasbourg), Rodrigo Ibata (Strasbourg), Pavel Kroupa (Bonn, Prague)

The dynamical stability of disk galaxies is sensitive to whether their anomalous rotation curves are caused by dark matter halos or Milgromian Dynamics (MOND). We investigate this by setting up a MOND model of M33. We first simulate it in isolation for 6 Gyr, starting from an initial good match to the rotation curve (RC). Too large a bar and bulge form when the gas is too hot, but this is avoided by reducing the gas temperature. A strong bar still forms in 1 Gyr, but rapidly weakens and becomes consistent with the observed weak bar. Previous work showed this to be challenging in Newtonian models with a live dark matter halo, which developed strong bars. The bar pattern speed implies a realistic corotation radius of 3 kpc. However, the RC still rises too steeply, and the central line of sight velocity dispersion (LOSVD) is too high. We then add a constant external acceleration field of 8.4×10−12 m/s2 at 30∘ to the disk as a first order estimate for the gravity exerted by M31. This suppresses buildup of material at the centre, causing the RC to rise more slowly and reducing the central LOSVD. Overall, this simulation bears good resemblance to several global properties of M33, and highlights the importance of including even a weak external field on the stability and evolution of disk galaxies. Further simulations with a time-varying external field, modeling the full orbit of M33, will be needed to confirm its resemblance to observations.%We finally discuss a novel observational test using the warp induced by the external field in nearly edge-on galaxies.

It shows science at work. MOND models do well at galaxy rotation curves.

Regards Andrew 

 

I wasn't aware of MOND and I found that account really interesting - thanks for posting that Andrew.  As as you say a good example of science at work .    There is useful background introduction  to MOND on wikiipedia for anybody interested.  https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

Jim 

1 minute ago, philthy said:

These could equally be evidence for an incorrect theory where dark matter doesn't exist

I'm sorry I don't see how that could be could you explain why that could be the case?

16 hours ago, Viktiste said:

When Newton's laws did not quite explain Mercury's orbit, Einstein came up with another theory. When Einstein's theory does not quite explain galaxies rotation speed, we come up with another theory dark matter. 

?

Not relaxing, but have had a beer 😀

I'm not sure he did.  His rationale for the theory of GR was a little wider than the problem with Mercury's orbit.  Mercury's orbit was used to test the new theory as it presented a measurable effect but I don't think it was the driver.  Look at the end of the day if dark matter is a piece of nonsense then we will find out , if it is not then we will find out.  If it needs a new theory then a new theory will emerge in time ,  that is how science works. Quite exciting either way but it's a long game.   I take it you are not keen on the concept of dark matter as part of the solution , could you explain why and maybe give some insight to where you think the focus of research should be?  I don't really have any strong opinions about it other than I detest the name dark matter and dark energy - it is a gift to pseudo science and lazy media hacks.  It also frightens children :) 

Jim 

We have some very good observational data which backs up GR , gravitational lensing being one of the more compelling I guess and gravitational red shift (1959 Robert Pound and Glen Rebka observed redshift in light in an experimental setup at Harvard Univesity).    So GR appears sound, while no doubt like all theories further layers of refinement may emerge in time, there is nothing really at the moment to suggest that it is significantly flawed.  The  high rotational speed of galaxies may ultimately be accounted for  by what they are calling "dark matter" (I really do wish they had used a different name) or even an error in measurement  of "normal matter"   time may tell. But certainly at the moment there is no basis (no evidence)  for laying  aside GR , it appears to make accurate predictions. 

Jim 

Blinky I'd be interested in finding the answer to that but on first inspection I wonder why not following calibration etc.  I've been thinking for some time to try some photometry work myself.  As well as Andrew's link to Brit Astronomical Association I wonder if you caught this by Matt Baker ( he posted on SGL the other day) - his site has a useful intro guide to transit data capture and processing.  Can I ask , possibly silly question, but what are the multiple lines , at first i thought colour channel but too many for that !  Is it repeated data runs against the same target ?

Jim 

https://www.mattsastro.co.uk/post/photographing-exoplanet-transits

On 12/11/2020 at 00:40, Drifter said:

Maybe the cause of lensing effects aren’t solely gravitational?
Chemicals, liquids between a light source can cause distortions

Imagine some mechanism out in space generating such pockets of refraction? 

Aren’t our observations ‘lensing’ through the ice fields of the Kuiper Belt?
 

That would be a simply unbelievable amount of liquid/chemicals to cause the extent of gravitational lensing recorded. Most improbable. 

Jim 

20 minutes ago, Paul M said:

I think the word "invented" is way too strong. Number theory quite clearly follows geometric rules. As I said above, everything in Physics can be expressed mathematically but that relationship isn't necessarily a two way street.

The example of imaginary numbers you gave is interesting and certainly beyond my grasp as a maths dunce. But there is a Pi in there and Pi is a geometrical entity if ever there was one. So doesn't that tie the rest of it to geometry?

My first encounter of imaginary numbers was in a now quite well know book by James Gleick: "Chaos", and was my first foray into fractals. Particularly the Mandelbrot Set, which I explored extensively (and very slowly  ) on my BBC micro using an algorithm I constructed myself based on my reading of that book. Imaginary numbers play a big role in fractals and by my reckoning fractals are geometrical entities. So we come full circle; maths being a language that quantifies the geometrical nature of physics.

Does the Mandelbrot Set reside in geometry or mathematics? (I think I just convinced myself that it's purely mathematical...  )

We do quiet regularly "force" or perhaps approximate geometry onto the real world in order to more easily model it mathematically.  What I mean is we often approximate the physical world by reducing it to a more convenient and expressible geometrical device - the classic "consider a spherical cow moment".    Maybe this will make better sense - when describing Irradiance which we define as power per unit area  , we start with the approximation of "a point source".  Light emitted from a point source propagates as a sphere and so the mathematics becomes determinable and produces the inverse square law I = kd^-2  derived from the area of a sphere 4 PI d^2.   So in a way we have artificially forced PI into the relationship and upon nature.   Point sources don't really exist (not in our macro world)  so the real or true relationship between Irradiance and distance is somewhat more complicated (for extended sources) than our simple approximation suggests.  I think I tend to agree with you Paul , from my experience much of our  Physics describing, certainly the classical world, is rooted in geometrical approximations. 

Jim 

17 minutes ago, vlaiv said:

Sure, it is very famous and often quoted as one of the most beautiful if not the most beautiful math equations:

https://en.wikipedia.org/wiki/Euler's_identity

 

I'd hazard a guess it has been much exercised by epidemiologists in the battle of Covid 19.  Here's to Euler and his equation  

Jim