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Since the universe is 13.8 billion years old, we are able to see objects which are 13.8 billion light years away. How are the physicists able to say that the di
by hi41 9y ago
Since the universe is 13.8 billion years old, we are able to see objects which are 13.8 billion light years away. How are the physicists able to say that the diameter is 93 billion light years? Shouldn't it be closer to 27.6 billion light years in diameter?
- simcop2387 9y agoSo as you've set things up, the radius of the sphere we can see is 13.8 billion light years. That means that the diameter of that sphere is 27.6 billion light years. But here's the rub, the visible parts are all moving away from us, so while we see them as being 13.8 billion light years away, they've been traveling for 13.8 billion years away from us. Along with that, the rate that they're traveling has been increasing the further away (in time and space) they are. Now since we've found ways to correlate the distance and velocity that things are traveling on large scales in the universe, we can actually figure out about how far away the objects we can see should be from us, after traveling 13.8 billion years. This is where the 93 billion light year figure comes from, how far away those "edges" have traveled since they emitted the light we see today.
- twtw 9y agoSpace has expanded in the interim.
- btilly 9y agoThe usual image is to picture light traveling through the universe as being like an ant crawling along an expanding balloon. The distance from where the ant is to the point that it started at is longer than the distance that it crawled. Because you have to add in how much the path expanded after the ant crawled past. In 13.8 billion years, light crawled 13.8 billion light years. However the point where it started is now roughly 45.5 billion light years away. Making the diameter of the visible universe 93 billion years. (In general relativity there are complications about what "now" means between distant points. But suffice it to say that there is a reasonable way that sensible people can agree on to make sense of it, and those are the answers that we arrive at.)
- v_lisivka 9y agoThey don't. Light from distant stars has red shift, similar to Doppler shift. IF this red shift is interpreted as Doppler shift, then we can calculate corresponding velocity and then calculate position of a star at today date, and we will see that visible Universe is expanding. However, we need to point to source of energy for that expanding (with acceleration!). Nobody able to find that source yet. IF this red shift is interpreted as something else (e.g. loses due to friction), then visible Universe is still.
- badosu 9y ago> IF this red shift is interpreted as something else (e.g. loses due to friction), then visible Universe is still. This is a pretty interesting idea, I wonder if a consistent model of EM frequency damping with distance traveled could be built.
- v_lisivka 9y agoIMHO, you don't need that. If you will accept that our Universe is «digital» in nature (i.e. you cannot have 1/2 of black hole or 1/2 of star, of 1/2 atom, etc.), then you will see that each photon can be represented by large _integer_ number. This means that photon will lose 2*1/2 of it smallest digit at each revolution at average. Exceeding energy will make vacuum «hot». It's all.
- pokemongoaway 9y agoBecause they just fudge the math to match the old theory. They're frauds that are uncomfortable with change. Changing the theory to match new data so many times over the last century and acting like the theory hasn't failed or really had to change at it's core (and when other theories have predicted CMB and other measurements more closely) is the definition of fraud in science.
- AstralStorm 9y agoIs it really? Are you arguing for attaching version numbers to theories? This is not someone in backyard presenting a random set of equations that are not interlinked as a theory. Not epicycles.
- pokemongoaway 9y agoI'm not arguing for that since anyone who is steeped in the topic can determine a general "change history." I didn't claim it was someone in their backyard, did I? No it is job stability. No one who doesn't believe in string theory will get a specialized degree in it, for example. HN seems open to criticizing generalities like, "science publications are often fabricated" or "academia is too closed," but you start getting too specific and the folks who have most of the academic budget for a mainstream paradigm will come out of the woodwork to discredit skeptics using straw man arguments, ad hominem attacks, and various disingenuous methods of thwarting reasonable opposition. For example, just look at the percentage of worldwide physics funding goes toward big bang based fields vs the rest.