Reddit reviews Cosmology

>So I was thinking to myself that Dark Energy seems like a seemingly, for someone like me at least, silly concept

oh thanks for your assessment on 50 years of cosmology research.

come back when you have read a book on cosmology.

https://www.amazon.com/Cosmology-Steven-Weinberg/dp/0198526822 (or your local library).

that book also discusses alternative explanations of observations in detail and shows why they can be rules out.

>As in, "Big Bangs" occuring across multiple regions, very far apart, couldn't the gravity of these individual "universes" cause something similar?

very sophisticated suggestion. tell me how that is different from "i dunno, it doesn't fit the equations, i haven't even checked, i just blabber random stuff that seemed to sound good."

>I'm not the sharpest tool in the shed, so forgive any logic fails I may have made. :I

the only thing you can be blamed for is not bothering to read up on what research has been done, yet commenting on it, calling it silly, and providing 3 vague half-baked sentences of how you would explain it. that's arrogance.

have a nice day.

Not sure if you've played then, but haven't: Kerbal Space Program is the best way to get an intuitive understanding of orbital mechanics. If you like to play God you should also try the Universe Sandbox, and if you want a really really hardcore space sim you should play (or wait, it's still in alpha) for Rogue System.


As for actual books, OpenStax recently published their free astronomy book, and it's quite good for an introduction. From there, it depends entirely on what you're interested in, there's literally a universe's worth of information about
Astrophysics,
Astrochemistry,
Astrobiology,
Astrometry and
Orbital mechanics (for the aspiring galactic navigator),
Cosmology,
Planetary geology and
Cosmochemistry (careful, these last two lead to geology and meteorology which are equally disastrously addictive fields!)


Also, feel free to follow NASA's, ESA's, and JAXA's blogs. And spend a minute each morning checking the astronomy picture of the day.


Just don't end up llike me and annoy all your friends.

>Ok let’s switch it. What if instead of slowing down because of the lack of energy the expansion acceleration is creating energy which will multiply exponentially on itself till the the closer you get to the finite end when the rubber has met its furthest possible expansion it snaps back creating the next bb

"Ok let's switch it. What if [proposal that doesn't fit what we observe, because i don't feel comfortable with that]."

how about we just go with our best knowledge instead?

>I’m sorry. I just don’t think the vacuum theory feels right

you are dismissing decades of solid science, observations, model building, testing the model experimentally on a gut feeling?

if your gut tells you to dismiss the work of people who have decades of education and then experience in them without even actually reading and working through that work, it may just be flatulence.

just read a book frankly.

https://www.amazon.com/gp/aw/d/0198526822/ref=mp_s_a_1_5?ie=UTF8&qid=1509881934&sr=8-5&pi=AC_SX236_SY340_FMwebp_QL65&keywords=cosmology&dpPl=1&dpID=415BiHVKprL&ref=plSrch

of course you'll need years of prerequisite physics classes.

Once you have read that you will probably be thirsty to dig a bit deeper. Weinberg hast to be a good option. He is probably one of greatest physicists of our time. Andrew Liddle has another book that takes things much further. It is still very accessible even though it goes into quite a lot of depth. The one downside is that there are quite a few mistakes in it.

Have you read Weinberg's Cosmology?

> It still can and is still evidence

When the vast majority of correlated sequences are not causually related, correlation alone is not evidence. It provides a safety test used to discard ideas early. Since the majority of correlated sequences are not related, taking correlation as evidence is more likely to represent non-casual events as opposed to causual events. Only when there is an underlying mechanism and/or all (or most) other competing theories have been discredited through experiment or observation do we conclude that the events are casual.

Think about that carefully: the vast majority (precisely, all but a set of measure zero on a suitable space) of correlated sequences are not casual. Picking a correlated sequence uniformly at random from empirical measurements has a 0% chance of being casual. 0%.

This link demonstrates the ludicrousness of claiming correlation is evidence. In this case is the correlation evidence that the hypothesis is true?

> Tons of theories are supported by nothing more than correlation. For instance, the main methods for finding distances to other galaxies are the Tully-Fisher relationship and the Fundamental Plain. Neither of these methods has any theoretical backing, both are merely empirically observed correlations.

Yeah, except that's wrong. Both have significant theoretical explanations underlying the mechanism. For example, grabbing Weinberg's Cosmology off my shelf explains the mechanism behind Tully-Fisher on page 25, and the Fundamental plane is an extension of the Faber-Jackson relation (page 27), which follows from theory (virial theorem, derived from basic physics on page 66). In both these examples we believe the correlation is from causation precisely because we have a solid theoretical back, and we have eliminated other competing theories. Saying "Neither of these methods has any theoretical backing" is nonsense. For one thing, if it were true, there'd be some PhDs available to anyone explaining it, and no one is working on explaining it anymore - it's done. People work on newer methods, or refinements.

> ind me a source that says we know for a fact that the universe is an infinite sheet.

Weinberg's book shows a proof that that the only flat, homogeneous and isotropic manifolds is the infinite sheet.

Also, the only person who would say that manifolds only have to have local properties like the universe we see are those that have no problems with fairies filling the universe as long as they don't locally. Think about it. Since homogeneity and isotropy for you only have to hold locally, there is nothing wrong with postulating the universe is full of fairies, just not locally.


Sure, if to make your case all you require is that the physics we observe only holds locally than there is nothing wrong with globally the universe being filled with fairies, Santa Clauses, not being isotropic or whatever floats your boat. But there is no reason to take these universes seriously and so there is no reason to conclude anything other than the universe is infinite, since this is the only universe that is compatible with observations, unless we say anything goes as long as it is not local.