Film, Media & TV2 mins ago
95 % Of The Universe
I keep reading on scientific websites that we don't know what 95% of the universe is made from?
Its all atoms isn't it?
What is this thing about anti-matter?
Can you explain it to me in laymens terms?
I just don't get that we don't know about what the universe is made of.
Its all atoms isn't it?
What is this thing about anti-matter?
Can you explain it to me in laymens terms?
I just don't get that we don't know about what the universe is made of.
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I just wanted to add to Kidas' post that:
(a) Dark Energy is, in fact, connected to the Cosmological constant, although how we don't exactly know. There's a fun prediction that you can fit on the back of an envelope, where the cosmological constant ought to be related to the energy of space-time, so you can estimate its size. Except, doing it this way you get an answer that doesn't match the observed value. At all. I think the error depends a little on certain assumptions, but even so the difference between the prediction and the actual value is worse than drawing a dot on a piece of paper and declaring that your dot is about the same size as the entire Universe.
b) Also, Dark Matter is a separate concept entirely from Dark Energy, and whilst it does enter the question of the expanding Universe, you can deduce the existence of Dark Matter even if you didn't know the Universe was expanding. The key test, instead, is in the rotation of galaxies. All galaxies rotate, and -- again -- the speed of rotation can be measured and related to the mass of the galaxy (as well as, more subtly, how the matter in a galaxy is spread out). Still, you get an error, and the explanation is that there is some "missing" matter that we can't see, but that does weigh a lot, in order to derive the proper rotating behaviour of galaxies.
In that sense, at least, Dark Matter and Dark Energy are "fudge" solutions to at least two separate problems. Although it's a little bit harsh to call it a fudge. It's better to make the following chain of deduction:
1. General Relativity works, because we tested it on e.g. the orbit of Mercury, the cool "Einstein Cross" effect (where the same star appears at least twice, and often four times, in the sky, if it is "behind" something heavy enough to bend light), and on the orbits of GPS satellites.
2. Because it works, then we should also be able to use it to describe the shape of the Universe and the behaviour of Galaxies, and trust the calculations to do so.
3. Assuming that all the matter we can see is the only matter in the Universe, it turns out that step (2) was wrong, and we can't explain the shape of the Universe after all.
4. Ergo, either all of physics is broken, or there was something missing that we can't see.
5. Making only the minimal assumptions about the things we can't see, we can fit the observations after all, and physics is fine after all.
Of course, the hunt is now on to explain in more detail what makes up the "things we can't see". But it's rather like a budgeting error: if you find that you can't account for all the income in your expenditure and savings column, then unless some git stole the missing cash, you know that it's around there somewhere...
(a) Dark Energy is, in fact, connected to the Cosmological constant, although how we don't exactly know. There's a fun prediction that you can fit on the back of an envelope, where the cosmological constant ought to be related to the energy of space-time, so you can estimate its size. Except, doing it this way you get an answer that doesn't match the observed value. At all. I think the error depends a little on certain assumptions, but even so the difference between the prediction and the actual value is worse than drawing a dot on a piece of paper and declaring that your dot is about the same size as the entire Universe.
b) Also, Dark Matter is a separate concept entirely from Dark Energy, and whilst it does enter the question of the expanding Universe, you can deduce the existence of Dark Matter even if you didn't know the Universe was expanding. The key test, instead, is in the rotation of galaxies. All galaxies rotate, and -- again -- the speed of rotation can be measured and related to the mass of the galaxy (as well as, more subtly, how the matter in a galaxy is spread out). Still, you get an error, and the explanation is that there is some "missing" matter that we can't see, but that does weigh a lot, in order to derive the proper rotating behaviour of galaxies.
In that sense, at least, Dark Matter and Dark Energy are "fudge" solutions to at least two separate problems. Although it's a little bit harsh to call it a fudge. It's better to make the following chain of deduction:
1. General Relativity works, because we tested it on e.g. the orbit of Mercury, the cool "Einstein Cross" effect (where the same star appears at least twice, and often four times, in the sky, if it is "behind" something heavy enough to bend light), and on the orbits of GPS satellites.
2. Because it works, then we should also be able to use it to describe the shape of the Universe and the behaviour of Galaxies, and trust the calculations to do so.
3. Assuming that all the matter we can see is the only matter in the Universe, it turns out that step (2) was wrong, and we can't explain the shape of the Universe after all.
4. Ergo, either all of physics is broken, or there was something missing that we can't see.
5. Making only the minimal assumptions about the things we can't see, we can fit the observations after all, and physics is fine after all.
Of course, the hunt is now on to explain in more detail what makes up the "things we can't see". But it's rather like a budgeting error: if you find that you can't account for all the income in your expenditure and savings column, then unless some git stole the missing cash, you know that it's around there somewhere...
In reality I suspect the only advantage I have over most people is that I started studying physics seriously when I was something like 8 or 9, and since then (on and off) I've been doing nothing but. Even despite my best efforts, around 20 years or so of hard work is bound to have some kind of payoff.
I've said it before -- this is well 'ard.
I've said it before -- this is well 'ard.
As Ive mentioned b4 Jim, my ex's son is now studying physics at uni and he always had an interest in this stuff as a kid, he was talking to me about multiverses and string theory etc at 10yrs of age. Just couldn't keep up with him. As stated, I think it takes a special kind of mind to wrap ur head around this stuff.
Just to complicate things further, this (published today on the BBC website) seems to muck some of the theories up!
http://
http://
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