Menu
News
All News
Dungeons & Dragons
Level Up: Advanced 5th Edition
Pathfinder
Starfinder
Warhammer
2d20 System
Year Zero Engine
Industry News
Reviews
Dragon Reflections
Columns
Weekly Digests
Weekly News Digest
Freebies, Sales & Bundles
RPG Print News
RPG Crowdfunding News
Game Content
ENterplanetary DimENsions
Mythological Figures
Opinion
Worlds of Design
Peregrine's Next
RPG Evolution
Other Columns
From the Freelancing Frontline
Monster ENcyclopedia
WotC/TSR Alumni Look Back
4 Hours w/RSD (Ryan Dancey)
The Road to 3E (Jonathan Tweet)
Greenwood's Realms (Ed Greenwood)
Drawmij's TSR (Jim Ward)
Community
Forums & Topics
Forum List
Latest Posts
Forum list
*Dungeons & Dragons
Level Up: Advanced 5th Edition
D&D Older Editions
*TTRPGs General
*Pathfinder & Starfinder
EN Publishing
*Geek Talk & Media
Search forums
Chat/Discord
Resources
Wiki
Pages
Latest activity
Media
New media
New comments
Search media
Downloads
Latest reviews
Search resources
EN Publishing
Store
EN5ider
Adventures in ZEITGEIST
Awfully Cheerful Engine
What's OLD is NEW
Judge Dredd & The Worlds Of 2000AD
War of the Burning Sky
Level Up: Advanced 5E
Events & Releases
Upcoming Events
Private Events
Featured Events
Socials!
Twitch
YouTube
Facebook (EN Publishing)
Facebook (EN World)
Twitter
Instagram
TikTok
Podcast
Features
Top 5 RPGs Compiled Charts 2004-Present
Adventure Game Industry Market Research Summary (RPGs) V1.0
Ryan Dancey: Acquiring TSR
Q&A With Gary Gygax
D&D Rules FAQs
TSR, WotC, & Paizo: A Comparative History
D&D Pronunciation Guide
Million Dollar TTRPG Kickstarters
Tabletop RPG Podcast Hall of Fame
Eric Noah's Unofficial D&D 3rd Edition News
D&D in the Mainstream
D&D & RPG History
About Morrus
Log in
Register
What's new
Search
Search
Search titles only
By:
Forums & Topics
Forum List
Latest Posts
Forum list
*Dungeons & Dragons
Level Up: Advanced 5th Edition
D&D Older Editions
*TTRPGs General
*Pathfinder & Starfinder
EN Publishing
*Geek Talk & Media
Search forums
Chat/Discord
Menu
Log in
Register
Install the app
Install
Community
General Tabletop Discussion
*Geek Talk & Media
Is Time Travel (going backwards) Possible?
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="freyar" data-source="post: 6042217" data-attributes="member: 40227"><p>The other thing I wanted to talk about (hope I'm coherent now, 'cause I'm way past bedtime) is KarinsDad's discussion with Morrus and others. I don't want to get into the whole thing about open-mindedness other than to make one point: I am a physicist by profession and know a lot of other physicists. With very few exceptions, we try to be open-minded in the sense of weighing every new idea. We might make quick judgements sometimes, we might disagree with each other's opinions, and sometimes we (either individually or as a community consensus) are wrong, but we have well-thought out reasons for those decisions nearly all the time. And, frankly, those reasons have to do with the data at hand.</p><p></p><p>But I do want to say a bit more about dark matter and alternatives, since that came up and it's an area of my research. Dark matter was first discovered about 80 years ago, like KarinsDad mentioned, but most scientists didn't pay much attention at the time because there wasn't enough data to demand it --- the observations could have been fluky in some way. So the first big "demand" for dark matter was the discovery that galaxies rotate faster than they ought to if (1) gravity works the way Newton and Einstein said and (2) there's just normal matter. But it works if you add a invisible, nearly pressureless form of matter that interacts via gravity with about 5 times as much total mass as normal matter. That's the how we define "dark matter." You can also describe galaxy rotation well if you change gravity. This is the idea of MOdified Newtonian Dynamics (MOND) and similar theories (I'll lump them together). However, you can also look at galaxies moving in clusters of galaxies. They also move faster than they "should" based on normal gravity and just normal matter. If you add 5 times as much dark matter, you get a prediction consistent with observation. If you use MOND, you also have to add some kind of invisible, nearly pressureless matter usually identified by MOND enthusiasts as neutrinos (from the Standard Model of particle physics). So MOND doesn't work perfectly on its own. Next, you can look at the cosmic microwave background light (CMB), which is the oldest light that's possible to see (any older, and the universe was opaque). It looks very uniform, but there are tiny variations in its temperature over the sky. Based on dark matter, people made detailed predictions for the patterns of the CMB years in advance of their measurement. These predictions match the measurements very well. For MOND to make these predictions, you need a relativistic version, and there are 2 problems: (1) it's not clear that the relativistic version of MOND is a self-consistent theory of physics as it looks pretty ugly and (2) there's controversy -- meaning conflicting calculations -- about whether it can predict (postdict now, maybe) the pattern of the CMB.</p><p></p><p>So, dark matter makes good predictions, MOND, not so much. Nonetheless, MOND is an intriguing option, so there are physicists still working on it, getting grants, etc. As long as there is a way it might fit the data, people will talk and think about it. But I hope I've explained why dark matter is the prevalent idea. It just works with the data, and it has the added bonus of being something that makes sense in terms of particle physics (I haven't gotten into that). I also hope you can see that it's not like what KarinsDad has said about Neptune's winds; it's not that we think we know what's going on and make a prediction in the absence of data (though that is supposed to be one part of the scientific method). There really is a lot of data consistent with and predicted by the dark matter hypothesis.</p></blockquote><p></p>
[QUOTE="freyar, post: 6042217, member: 40227"] The other thing I wanted to talk about (hope I'm coherent now, 'cause I'm way past bedtime) is KarinsDad's discussion with Morrus and others. I don't want to get into the whole thing about open-mindedness other than to make one point: I am a physicist by profession and know a lot of other physicists. With very few exceptions, we try to be open-minded in the sense of weighing every new idea. We might make quick judgements sometimes, we might disagree with each other's opinions, and sometimes we (either individually or as a community consensus) are wrong, but we have well-thought out reasons for those decisions nearly all the time. And, frankly, those reasons have to do with the data at hand. But I do want to say a bit more about dark matter and alternatives, since that came up and it's an area of my research. Dark matter was first discovered about 80 years ago, like KarinsDad mentioned, but most scientists didn't pay much attention at the time because there wasn't enough data to demand it --- the observations could have been fluky in some way. So the first big "demand" for dark matter was the discovery that galaxies rotate faster than they ought to if (1) gravity works the way Newton and Einstein said and (2) there's just normal matter. But it works if you add a invisible, nearly pressureless form of matter that interacts via gravity with about 5 times as much total mass as normal matter. That's the how we define "dark matter." You can also describe galaxy rotation well if you change gravity. This is the idea of MOdified Newtonian Dynamics (MOND) and similar theories (I'll lump them together). However, you can also look at galaxies moving in clusters of galaxies. They also move faster than they "should" based on normal gravity and just normal matter. If you add 5 times as much dark matter, you get a prediction consistent with observation. If you use MOND, you also have to add some kind of invisible, nearly pressureless matter usually identified by MOND enthusiasts as neutrinos (from the Standard Model of particle physics). So MOND doesn't work perfectly on its own. Next, you can look at the cosmic microwave background light (CMB), which is the oldest light that's possible to see (any older, and the universe was opaque). It looks very uniform, but there are tiny variations in its temperature over the sky. Based on dark matter, people made detailed predictions for the patterns of the CMB years in advance of their measurement. These predictions match the measurements very well. For MOND to make these predictions, you need a relativistic version, and there are 2 problems: (1) it's not clear that the relativistic version of MOND is a self-consistent theory of physics as it looks pretty ugly and (2) there's controversy -- meaning conflicting calculations -- about whether it can predict (postdict now, maybe) the pattern of the CMB. So, dark matter makes good predictions, MOND, not so much. Nonetheless, MOND is an intriguing option, so there are physicists still working on it, getting grants, etc. As long as there is a way it might fit the data, people will talk and think about it. But I hope I've explained why dark matter is the prevalent idea. It just works with the data, and it has the added bonus of being something that makes sense in terms of particle physics (I haven't gotten into that). I also hope you can see that it's not like what KarinsDad has said about Neptune's winds; it's not that we think we know what's going on and make a prediction in the absence of data (though that is supposed to be one part of the scientific method). There really is a lot of data consistent with and predicted by the dark matter hypothesis. [/QUOTE]
Insert quotes…
Verification
Post reply
Community
General Tabletop Discussion
*Geek Talk & Media
Is Time Travel (going backwards) Possible?
Top