Leaderboard

Continuing the calculations by Mordred and swansont: The sun's spectrum peaks in the visible range, so let's guess that its visible output is on the order of 1025J/sec. The energy of a visible photon is roughly hf = 10-33Jsec * 1017/sec = 10-16J. So the output of visible photons is 1025J/sec / 10-16J = 1049 per second. One light-year = 3*108m/sec * 3600 * 24 * 365 sec = 1016m. The diameter of our galaxy is D = 100,000 light-years = 1021m. The area of the spherical shell the photons pass through is roughly 10 D2 = 1043m2. The area of a 6-inch telescope is about 0.01 m2. So the area ratio is 10-2 / 1043 = 10-45. And finally, the rate at which visible photons reach the telescope from a star on the other side of the Milky Way is: 10-45 * 1049/sec = somewhere in the vicinity of 10,000 visible photons per second. Of course, this is only a rough guess, and different stars have different parameters, so let's say it's probably at least about 1000 per second, and maybe as many as 100,000, for an amateur telescope and an average star somewhere in the middle of the galaxy.

Your opening post contained an assertion that I challenged since it is not completely true. I gave you a counterexample. I did not only answer your question but posted in such a way as could not be (I thought) mistaken for anything other than an answer to the question you asked, which I identified by the question mark you provided in your opening post. Apart from the mathematical versions of the above examples, what about statistics and probability ? This time I provided two further counter examples to the false statement you started with as pertinent to explaining why I made the answer I did.

Just to clarify this last bit. We're not descended from dinosaurs. About 320 million years ago the ancestors of both humans and dinosaurs were to be found among a group of related small lizard-like creatures. One of these had made a few readjustments to its skull to improve the efficiency of its bite. It may have been a creature called Archaeothyris found in Nova Scotia, or a species very closely akin to this, and we (along with all other mammals) are their descendents. Dinosaurs and all other modern reptiles are descended from one of the species that had not developed this advanced bite.

Another thing I forgot about. Maybe someone can discuss what affected survival rates.

When the asteroid hit, today's Mexico and East Africa were not where they are now. They were much closer to each other, separated by only about 80 degrees of longitude. Anyway, the extinction event was global, affecting the entire planet, but differentially affecting different life lineages.

Hah! So I was right in the first place. I guess that makes sense, given how closely they resemble modern mammals. Thanks.

Er, well, mastodons, sabre-toothed tigers, etc. appeared about 40m or more years later, from the Miocene onwards. The mammals that existed at the end of the Cretaceous were indeed small and shrew-like.

Except for sabre-toothed tigers, mastodons, and/or probably other species. 🙄 Maybe it would be more accurate to say that some mammal species were small and at least some of the small ones survived. Also, the asteroid supposedly hit in Mexico, and our ancestors came from Africa, which is on the other side of the planet. So maybe there weren't quite as many extinctions on that continent.

Ok, thanks for clearing that up, appreciate your time

No, there was an extinction event. I think most mammals were relatively small back then. Lots of them, so I guess a few must have survived.

Placentalia existed at the same time as dinosaurs. They're mammals. Apparently the fossil evidence is a bit thin, but if you start with primates (or humans) and work your way back, placentalia are our closest ancestors that were alive 100 million years ago. Apparently the connection between mammals and dinosaurs dates back to amniotes, about 300 million years ago.

Uneven mass distribution does contribute, but the effect is small. It’s been measured. https://en.m.wikipedia.org/wiki/Gravity_of_Earth

This is particularly @Ghideon Now that that the repair is done and forgotten here is an update. The river has been in spate over the weir system during the last few days and I observed the different flowpatterns at the failure point abd the rest of the weir sidewalls. The first photo is the normal laminar flow as it tumbles over the weir, ducks down in a U, rises up again and carries on in the same direction. In the second photo against the failure wall, the water ducks down, rises backs up and flows back over the top of itself forming a vortex with a horizontal axis perpendicular to the wall. I have indicated the difference with flow arrows on the pictures. I would imagine that the vortex picks up small stone which grind against the sidewall constantantly boring into it along the axis line.

The particles don't go through both slits but as a particle goes through one slit, its virtual antiparticle goes through the other. The predictions of this is that the particles form an interference pattern on a screen.