Online reading group and book discussion forum
  HOME ENTER FORUMS OUR BOOKS LINKS DONATE ADVERTISE CONTACT  
View unanswered posts | View active topics It is currently Wed Dec 13, 2017 3:37 pm





Post new topic Reply to topic  [ 3 posts ] • Topic evaluate: Evaluations: 0, 0.00 on the average.Evaluations: 0, 0.00 on the average.Evaluations: 0, 0.00 on the average.Evaluations: 0, 0.00 on the average.Evaluations: 0, 0.00 on the average. 
Ch. 6: Dark Energy 
Author Message
User avatar
Years of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membership
BookTalk.org Hall of Fame

BookTalk.org Owner
Diamond Contributor 3

Joined: May 2002
Posts: 15658
Location: Florida
Thanks: 3203
Thanked: 1207 times in 955 posts
Gender: Male
Country: United States (us)
Highscores: 6

 Ch. 6: Dark Energy
Astrophysics for People in a Hurry
by Neil deGrasse Tyson

Ch. 6: Dark Energy


Please use this thread to discuss this chapter.



Thu Oct 12, 2017 2:37 pm
Profile Email WWW
User avatar
Years of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membership
Authors are MY fans!

BookTalk.org Moderator
Silver Contributor

Joined: Jul 2002
Posts: 1829
Location: Cincinnati, OH
Thanks: 53
Thanked: 620 times in 484 posts
Gender: Male
Country: United States (us)

Post Re: Ch. 6: Dark Energy
Quote:
As if you didn’t have enough to worry about, the universe in recent decades was discovered to wield a mysterious pressure that issues forth from the vacuum of space and that acts opposite cosmic gravity. Not only that, this “negative gravity” will ultimately win the tug-of-war, as it forces the cosmic expansion to accelerate exponentially into the future.

In the previous chapter NDT discussed the opposing forces of coagulation and dilution. Up until very recently, everyone believed the universe is a steady-state, not expanding or contracting. In the 1920s and 30s Edwin Hubble observed the expansion of the universe. Next came a raging question of whether it expands forever or contracts periodically. Now we have that answer due to measurements of the effects of dark energy.
Quote:
Since both mass and energy cause space-time to warp, or curve, omega tells us the shape of the cosmos. If omega is less than one, the actual mass-energy falls below the critical value, and the universe expands forever in every direction for all of time, taking on the shape of a saddle, in which initially parallel lines diverge. If omega equals one, the universe expands forever, but only barely so. In that case the shape is flat, preserving all the geometric rules we learned in high school about parallel lines. If omega exceeds one, parallel lines converge, and the universe curves back on itself, ultimately recollapsing into the fireball whence it came.

We know omega does equal one, but only after considering the huge amount of dark energy in the universe. This was understood only after very detailed measurements showed the expansion of the universe is accelerating, a paradox that lead towards dark energy.
Quote:
In a trillion or so years, anyone alive in our own galaxy may know nothing of other galaxies. Our observable universe will merely comprise a system of nearby, long-lived stars within the Milky Way. And beyond this starry night will lie an endless void—darkness in the face of the deep.

A potentially depressing thought, but they won't know any better. :? 8)



Sat Dec 02, 2017 2:45 pm
Profile
User avatar
Years of membershipYears of membershipYears of membershipYears of membershipYears of membershipYears of membership
Better Thread Count than Your Best Linens


Joined: May 2011
Posts: 632
Thanks: 476
Thanked: 269 times in 222 posts
Gender: None specified

Post Re: Ch. 6: Dark Energy
Hard to get excited about anything this new, this tenuously connected to observed mechanisms, and this unknown. "Dark energy" is likely to be in a category of outdated terms like "phlogiston" within 30 years, and could very well turn out to be a kludge made up to solve a number of problems which are actually not related as closely as the current thinking implies.

The idea that the universe somehow attains "flatness" (i.e. not negatively curved and not positively curved) by the same mechanism which explains the observed acceleration of the expansion of the universe seems like a cool coincidence. But it could be that Guth's "inflationary universe" is not as currently conceived, and so the flatness has some artificiality to it, or at least something that does not make it the most likely outcome of the "inflationary" mechanism (which has some observational confirmation in the evenness of the Microwave Background Radiation). It could also be that other factors are interacting of which we are not yet aware, leading our parsimonious approach to neglect some further factor. After all, 20 years ago we did not know the expansion was speeding up.



Sat Dec 09, 2017 1:12 pm
Profile Email
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] • Topic evaluate: Evaluations: 0, 0.00 on the average.Evaluations: 0, 0.00 on the average.Evaluations: 0, 0.00 on the average.Evaluations: 0, 0.00 on the average.Evaluations: 0, 0.00 on the average. 



Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:

BookTalk.org Newsletter 



Site Resources 
HELPFUL INFO:
Forum Rules & Tips
Frequently Asked Questions
BBCode Explained
Author Interview Transcripts
Be a Book Discussion Leader!

IDEAS FOR WHAT TO READ:
Bestsellers
Book Awards
• Book Reviews
• Online Books
• Team Picks
Newspaper Book Sections

WHERE TO BUY BOOKS:
• Great resource pages are coming!

BEHIND THE BOOKS:
• Great resource pages are coming!

PROMOTE YOUR BOOK!
Advertise on BookTalk.org
How To Promote Your Book

Featured Books

Books by New Authors


*

FACTS is a select group of active BookTalk.org members passionate about promoting Freethought, Atheism, Critical Thinking and Science.

Apply to join FACTS
See who else is in FACTS







BookTalk.org is a thriving book discussion forum, online reading group or book club. We read and talk about both fiction and non-fiction books as a community. Our forums are open to anyone in the world. While discussing books is our passion we also have active forums for talking about poetry, short stories, writing and authors. Our general discussion forum section includes forums for discussing science, religion, philosophy, politics, history, current events, arts, entertainment and more. We hope you join us!



Copyright © BookTalk.org 2002-2017. All rights reserved.
Display Pagerank