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# Tiki

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1. ## How was the Universe created? How will it end or will it end?

Perhaps this forum could benefit from another sticky: 'The Conceptual Limits of Science'
2. ## Cooldown time c8 vs c9.25

If a c9.25 is simply a scaled up version of a c8 then the c9.25 would take approximately 15% longer to cool down. ( The amount of heat in a 9.25 is about 1.5 more than a c8, but the larger surface area of the 9.25 is better able to disperse the heat)
3. ## Gravitational wave doubt

It is worth pointing out that gravitational waves are very subtle in their nature. Einstein himself was not always convinced of their existence, so if you don't understand gravitational waves you are in very good company to say the least. It was not until the 50's and 60's that much of the details were worked out. The tidal effect described by acey above is Newtonian and has nothing to do with gravitational waves (assuming that the elevator is somewhere on the earth). The Earth's gravitational field, being spherically symmetric is independent of time. Time varying gravitational fields give rise to gravitational waves eg. Binary pulsars/black holes, the collapse of stellar cores, black hole mergers. In the unlikely event of a perfectly symmetric collapse of a star then no gravitational waves would be emitted. As Paul M points out above, gravitational waves are transverse. This is key to their understanding. Suppose we knew that the sun was about to act completely out of character and emit some gravitational waves. In order to best detect them we would configure our apparatus in the tangent plane. If we aligned our apparatus radially then we would detect nothing. Our apparatus in this case could consist of a bar and we would be looking for deformations of the order of 1 part in 10^21. Early detectors were commonly of the 'bar' type. I hope this helps. Electro magnetic waves are the closest analogy to gravitational waves but the manner in which they interact with matter is somewhat different.
4. ## If the universe is infinite why can't i see stars everywhere I look?

Top drawer. Three things particularly impress me about Feynman: his scientific integrity, his scientific intuition and his ability as a mathematician.

I drive on the A351 and head off westwards at Stoborough passing over Grange Hill. I'm afraid I don't know of any toll road.

What a night you had Stu, Sagittarius is something special indeed.I had an excellent night myself just down the coast at Kimmeridge a month or so ago. M24 was particularly beautiful I recall.
7. ## If the universe is infinite why can't i see stars everywhere I look?

I forget who (Eddington perhaps), but someone famous did say: " All science is physics, everything else is just stamp collecting"
8. ## What is a force ?

Isn't this what Einstein did: he expressed the curvature of spacetime in terms of local tidal forces.
9. ## What is a force ?

The gravitational force is of course relatively weak. eg. The ratio of the gravitational force to the electrical force is of the order -10^43 for two electrons.
10. ## What is a force ?

We can also use force to define fields. Eg. Lorenz force in elecro-magnetic theory.
11. ## Would you get the exact same universe from a common starting point?

Perhaps we are all playthings of chance. A non-limp wristed roll of the dice should suffice for a random outcome. In "idealized snooker", no friction/air resistance, with cueing as accurately as allowed by The Uncertainty Principle, Newton's Laws would be useless to us after the struck ball had made ten successive collisions.
12. ## If the universe is infinite why can't i see stars everywhere I look?

I am not 100% sure, but I think the method that Eratosthenes used was as follows: There was a well which upon a certain day used to be illuminated all the way down by direct sunlight. Eratosthenes (I think), measured the height of the sun on the same day and in conjunction with his distance from the well was able to calculate the radius of the earth. Neat.
13. ## Aluminium vs steel

Your tube will be fine as it is. A proper structural core would significantly increase the rigidity of your tube. The core would need to be virtually incompressible and properly bonded to the tube walls. 'Builders pour foam' would therefore be useless. (Medium grade structural foam is very hard to mark with your fingernail.) Good luck with your project.
14. ## Wave-Particle Duality

Feynman on wave/particle duality: http://www.youtube.com/watch?v=hUJfjRoxCbk. Feynman is an excellent teacher.
15. ## Explaining expansion.

No-one knows what the 'Universe expands into' as we can't yet see beyond the CMB radiation. If cosmologists were able to hit upon the 100% correct model of the universe the prediction of 'what the universe expands into' would sadly be unverifiable by observation. Not only does space seemingly grow, it also changes the manner in which it accommodates the passage of photons (cosmological redshift). It seems more natural to say that space 'stretches'. Prof. Bernard Schutz's 'Gravity from the ground up' would interest you I am sure. Schutz is a first-rate teacher. http://www.gravityfromthegroundup.org/
16. ## Parabolic or spherical mirror, how can you tell?

It might be helpful to look at the 'Optical Testing' section about 2/3 of the way down this page https://stellafane.org/tm/atm/index.html. The difference between parabolic and spherical mirrors are so small that diffraction tests are the simplest way of inferring the true shape of a mirror. A parabolic mirror will reflect incoming parallel rays of light (eg. from a star) to a point whereas the reflected rays in a spherical mirror will be a bit spread out (spherical aberration). I hope this helps.
17. ## Bought my first telescope

Nice setup. Just right for lugging into the garden for a quick peek upwards. As for advice, I'd say plan your observing sessions beforehand and be sure to spend some time sweeping the Milky Way with your lowest power EP. Enjoy.
18. ## North America nebula: what should I see?

I usually star with zeta Cygni (mag 3.5ish) and then pan about a quarter of the way towards Deneb. This takes you to the 'Gulf of Mexico' and using this as a reference point I try and trace out the edges.
19. ## Gravitational wave doubt

If it's 'too good to be true' it often is. I'm sure that gravitional waves will be detected one day but I do wonder how as gravity is such a weak force. From the Scientific American link in Acey's original post: "In the ensuing two months, the doubts have only grown stronger, as physicists have attempted, and failed, to reproduce the BICEP2 team’s calculations—admittedly, without the original data, which the team hasn’t yet provided, and without the “systematics” paper, laying out the possible sources of error, which the team has promised but not yet completed. The paper describing the results themselves has not yet been published by a peer-reviewed journal, although that process is underway."
20. ## If the universe is infinite does that mean there is an infinite number of "me"s?

If mathematicians are happy [overjoyed] with the the ''concept of infinity" then perhaps we should be too. After all, mathematicians are on the whole a pretty skeptical bunch. To avoid most confusing aspects of "infinity" I remember to myself: Infinity is NAN (not a number).
21. ## Are black holes real?

Thanks for posting. If I understand correctly then the contention is that 'stellar collapse does not lead to BH formation' rather than 'BH's do not exist'.
22. ## Dob mount proportions

Me too. Mine is a bit wide so i'll have to trim it down. I am still undecided on azimuth bearing material but I won't need to decide just yet...
23. ## Dob mount proportions

Plenty to think about still, although I am now in a position to start a bit of wood butchery. The "Dobstuff" site has some useful piccys. http://www.dobstuff.com/assemble.htm I noticed that "Dobstuff" use a relatively coarse laminate/large Teflon bearing for azimuth. I was intending to use smaller (1"ish) square pads and some very matt formica. Any thoughts?
24. ## Excellent seeing on South Coast

Of late, whenever the sky is decently clear the moon is out . Last night though I had some excellent views of Saturn over the rooftops. It is not very often that I can go up to 216x without loss of contrast. A night to remember: sustained views of the Cassini division and some surface features were visible. Not bad for such a measly altitude. It did get very dewy though...
25. ## If the universe is infinite does that mean there is an infinite number of "me"s?

If the Universe were infinite then the sky would be bright at night. Google "Olbers paradox".
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