{"id":41492,"date":"2014-03-22T16:15:13","date_gmt":"2014-03-22T22:15:13","guid":{"rendered":"http:\/\/hill-kleerup.org\/blog\/2014\/03\/22\/and-leons-getting-laaaaarger.html"},"modified":"2014-03-23T10:58:27","modified_gmt":"2014-03-23T16:58:27","slug":"and-leons-getting-laaaaarger","status":"publish","type":"post","link":"https:\/\/hill-kleerup.org\/blog\/2014\/03\/22\/and-leons-getting-laaaaarger.html","title":{"rendered":"And Leon's getting LAAAAARGER!"},"content":{"rendered":"
It's not that everything is moving through space away from each other — it's that space itself<\/i> is expanding without any any actual spatial movement at all.<\/p>\n

Which is … mind-blowing, if not mind-expanding.<\/p>\n

(h\/t +<\/span>Kee Hinckley<\/a><\/span>)<\/p>\n

Reshared post from +Brian Koberlein<\/a><\/strong><\/p>\n

Traveling Without Moving<\/b><\/p>\n

With all the news about BICEP2 and the possible detection of early inflation, there have been a lot of misconceptions about what inflation actually is. \u00a0One of the biggest is the idea that during inflation the universe expanded faster than light. \u00a0It\u2019s a misconception that even many experts get wrong, and is so common that there\u2019s a technical arxiv paper addressing these misconceptions. \u00a0It\u2019s easy to see how this misconception arises. \u00a0After all, during inflation, two atoms a meter apart just before would find themselves about a light year apart within a fraction of a second. \u00a0How is that not moving faster than light? \u00a0It all has to do with the subtlety of general relativity.<\/p>\n

Before we talk about inflation, let\u2019s talk about a similar effect we see in the universe today, known as cosmic expansion. \u00a0When we look at distant galaxies, we see that the light of more distant galaxies is redshifted more than closer galaxies. \u00a0Now we know that light can be redshifted when objects move away from us, known as the Doppler effect. \u00a0For this reason, this effect is often described as galaxies moving away from us. \u00a0But redshift can also occur due to the expansion of space itself. \u00a0That is, space expands, but the galaxies aren\u2019t moving through space. \u00a0The first is a property of special relativity, and is due to the motion of objects through space. The second is a property of general relativity, and is due to an expansion of space.<\/p>\n

Since both effects give a redshift to distant galaxies, how do we know that cosmic expansion is due to an expansion of space and not relative motion? \u00a0If the redshift were due to relative motion, then the light of distant galaxies would be redshifted when leaving the galaxy, and that means the light would also appear dimmer. \u00a0If the redshift is due to cosmic expansion, then light leaves a distant galaxy without being redshifted, and therefore also not dimmed. \u00a0Only later is the light redshifted due to expansion. \u00a0This means you can compare the brightness of distant supernovae with their redshift, known as the magnitude-redshift relation. \u00a0What we find is that the magnitude-redshift relation matches expansion extraordinarily well. \u00a0It doesn\u2019t match the relative motion model at all.<\/p>\n

So we know that space is actually expanding, but what does that actually mean?<\/p>\n

Cosmic expansion is determined by what is known as the Hubble constant. \u00a0Currently our best measurement of the Hubble constant is about 20 km\/s per million light years. \u00a0This means that two points in space a million light years apart are moving away from each other at 20 kilometers each second. \u00a0Since all of space is expanding, the greater the distance between two points in space, the faster they move apart. \u00a0So two points 10 million light years apart are moving away at 200 km\/s, and so on. \u00a0Because of this, if you consider two points far enough apart, they will be moving away from each other faster than the speed of light. \u00a0The speed of light is about 300,000 km\/s, which, given our current Hubble constant is the separation speed for two points 15 billion light years apart.<\/p>\n

Now you might think then that a galaxy 16 billion light years away from us must be moving away from from us faster than light. \u00a0You could say that the the galaxy appears to be moving faster than light, but in actuality it is space that is expanding between us. \u00a0The galaxy itself isn\u2019t moving much at all. \u00a0It\u2019s not as if that distant galaxy is defying relativity. \u00a0After all, from that distant galaxy\u2019s perspective we are moving away from it faster than the speed of light. \u00a0The key point to remember is that this is due to cosmic expansion, not galactic motion. \u00a0And cosmic expansion is not faster than light, even though very distant objects can appear to be moving faster than light.<\/p>\n

Which brings us to inflation. \u00a0Many of the popular articles unfortunately state that during inflation the Universe was expanding faster than light, which isn\u2019t true. \u00a0What is true is that during inflation the rate of spatial expansion was much larger. \u00a0This means that the distance at which objects appear to move apart faster than light is much smaller, but it does not mean that the Universe expanded faster than light.<\/p>\n

We still don\u2019t understand the mechanism that triggered inflation, but we do know that inflation doesn\u2019t violate the speed of light. \u00a0During inflation the rate of expansion was tremendous, but even today space continues to expand, just at a much smaller rate.<\/p>\n

Image:<\/b> \u00a0Cosmic Inflation by Don Dixon.<\/p>\n

Paper:<\/b> Tamara M. Davis, Charles H. Lineweaver. Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe. arXiv:astro-ph\/0310808 (2003).\ufeff<\/p><\/blockquote>\n<\/div>\n

<\/div>\n

<\/p>\n

View this post on Google+<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

It's not that everything is moving through space away from each other — it's that space itself is expanding without any any actual spatial movement at all. Which is … mind-blowing, if not mind-expanding. (h\/t +Kee Hinckley) Reshared post from +Brian Koberlein Traveling Without Moving With all the news about BICEP2 and the possible detection … Continue reading “And Leon's getting LAAAAARGER!”<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":41493,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"","_seopress_titles_title":"","_seopress_titles_desc":"","_seopress_robots_index":"","_seopress_analysis_target_kw":"","_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[106,6,82],"tags":[],"class_list":["post-41492","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-plusposts","category-science","category-space"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/hill-kleerup.org\/blog\/wp\/wp-content\/uploads\/2014\/03\/cosmic-inflation-don-dixon.jpeg.jpg","jetpack_sharing_enabled":true,"jetpack-related-posts":[{"id":13513,"url":"https:\/\/hill-kleerup.org\/blog\/2008\/11\/25\/pretty_soon_it_adds_up_to.html","url_meta":{"origin":41492,"position":0},"title":"Pretty soon it adds up to real money …","author":"***Dave","date":"Tue 25-Nov-08 12:07pm","format":false,"excerpt":"The cost of the economic bail-out to date: If we add in the Citi bailout, the total cost now exceeds $4.6165 trillion dollars. People have a hard time conceptualizing...","rel":"","context":"In "Big Business"","block_context":{"text":"Big Business","link":"https:\/\/hill-kleerup.org\/blog\/category\/big-business"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":10898,"url":"https:\/\/hill-kleerup.org\/blog\/2007\/05\/23\/potpourri_for_the_feast_o.html","url_meta":{"origin":41492,"position":1},"title":"Potpourri for the Feast of St Ivo","author":"***Dave","date":"Wed 23-May-07 8:45pm","format":false,"excerpt":"Who was St Ivo? 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But it looks like it's more than just a nebulous \"Ranchers should get all the land (for Liberty and Profit),\" and that it's no coincidence the building they took over.Per CNN (http:\/\/goo.gl\/i95w4R), quoting Ammon\u2026","rel":"","context":"In "~PlusPosts"","block_context":{"text":"~PlusPosts","link":"https:\/\/hill-kleerup.org\/blog\/category\/blogging\/plusposts"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":6017,"url":"https:\/\/hill-kleerup.org\/blog\/2004\/06\/06\/party_time.html","url_meta":{"origin":41492,"position":5},"title":"Party time","author":"***Dave","date":"Sun 6-Jun-04 11:02pm","format":false,"excerpt":"A rather depressing NYT Op-Ed from David Brooks about how partisanship blinds everyone, regardless of party. 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