13,75 vs 78, 93, 820
Enligt dagens forskning är universum ca 13,75 miljarder år gammalt. Det betyder att den stora smällen gick av stapeln för så länge sedan. Det är lätt att med denna siffra tro att det synliga universums diameter då blir dubbelt så stor - fotoner spreds i alla riktningar och har färdats i 13,75 miljarder år. Ändå säger man att det observerbara universum är bra mycket större (vissa säger 78 miljarder ljusår, andra 93. Jag har till och med hört ett bud på 820). En väldigt vanlig fråga är; Hur i hela friden kan detta komma sig?
According to general relativity, space can expand faster than the speed of light, although we can view only a small portion of the universe due to the limitation imposed by light speed. Since we cannot observe space beyond the limitations of light (or any electromagnetic radiation), it is uncertain whether the size of the Universe is finite or infinite.
Slänger även in ett intressant svar på detta "påstående": "... the universe has been expanding for 13.7 billion years, the total diameter of the universe, as a result of the additive expansions, is about 43 billion light years across."
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"the estimate I think you are quoting is 46-47 billion lightyears and it is a RADIUS figure, not a diameter. That length is technically known as the particle horizon and it is the distance from us today, at the present moment, of the most distant particles that we can in principle be seeing today.
So that figure of 46-some billion LY is the radius of what is known as the (currently) observable universe.
It is confusing to speak of 46+ billion LY as "the radius of the universe" because it misleads people into thinking that it is the radius of the whole universe. It is not. The actual universe is known to be larger, and may indeed be infinite
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46+ billion LY is the current distance from us of farthest particles which today we could be pointing a dish or wave-detector or neutrino-eyeball at and at this moment be getting signals from. I speak figuratively about the technology.
Present technology has a way to go. At the present we dont have sensitive enough eyeballs and all we can see are particles which are 45 billion LY away. These are what sent us the light which eventually (after 13-some billion years) is being received by us as the cosmic microwave background. So we actually see 45, with present technology, and we could see 46. if we had instruments that could see stuff in the throes of the biggiebang.
In effect, 46+ billion LY is just the current size of a big ball with us as center which we call the (currently) observable universe.
the actual sure enough universe is bigger than that ball, and does not appear to have a center or a boundary, our notions of it are preliminary and somewhat vague.
If it is not infinite, which it could well be, then according to 2007 'best fit' to the available data it could have a circumference of
820 billion LY. This is a wildass guess which a professional, Ned Wright, just barely hinted at in a Jan 2007 scholarly paper if you read between the lines. At one point he gives a 'best fit' estimate of the overall curvature if the thing turns out to be finite and he does not translate that into a circumference, but 810-820 is what you get if you do translate."
"Keep looking up"
According to general relativity, space can expand faster than the speed of light, although we can view only a small portion of the universe due to the limitation imposed by light speed. Since we cannot observe space beyond the limitations of light (or any electromagnetic radiation), it is uncertain whether the size of the Universe is finite or infinite.
Slänger även in ett intressant svar på detta "påstående": "... the universe has been expanding for 13.7 billion years, the total diameter of the universe, as a result of the additive expansions, is about 43 billion light years across."
----------------------------------------------------------------
"the estimate I think you are quoting is 46-47 billion lightyears and it is a RADIUS figure, not a diameter. That length is technically known as the particle horizon and it is the distance from us today, at the present moment, of the most distant particles that we can in principle be seeing today.
So that figure of 46-some billion LY is the radius of what is known as the (currently) observable universe.
It is confusing to speak of 46+ billion LY as "the radius of the universe" because it misleads people into thinking that it is the radius of the whole universe. It is not. The actual universe is known to be larger, and may indeed be infinite
=====================
46+ billion LY is the current distance from us of farthest particles which today we could be pointing a dish or wave-detector or neutrino-eyeball at and at this moment be getting signals from. I speak figuratively about the technology.
Present technology has a way to go. At the present we dont have sensitive enough eyeballs and all we can see are particles which are 45 billion LY away. These are what sent us the light which eventually (after 13-some billion years) is being received by us as the cosmic microwave background. So we actually see 45, with present technology, and we could see 46. if we had instruments that could see stuff in the throes of the biggiebang.
In effect, 46+ billion LY is just the current size of a big ball with us as center which we call the (currently) observable universe.
the actual sure enough universe is bigger than that ball, and does not appear to have a center or a boundary, our notions of it are preliminary and somewhat vague.
If it is not infinite, which it could well be, then according to 2007 'best fit' to the available data it could have a circumference of
820 billion LY. This is a wildass guess which a professional, Ned Wright, just barely hinted at in a Jan 2007 scholarly paper if you read between the lines. At one point he gives a 'best fit' estimate of the overall curvature if the thing turns out to be finite and he does not translate that into a circumference, but 810-820 is what you get if you do translate."
"Keep looking up"
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