I like to think that whenever I drink water, I drink Mickey Mouse heads.

Earth - You are here.

See? It's educational!

how do they know how old the universe is

Water molecules look like mickey mouse heads ... lol

Our universe is 930 Septillion Metres in diameter. Would you look at all those nebulas and stuff. WTF are the pillars of creation? This stuff is so damn fascinating!

That took much longer to read than anticipated.

By looking at the size of the observable universe, looking at the rate of expansion and doing the maths backwards.

I want to know how they estimate how big the universe is beyond the observable part.

how do they know what the rate of expansion is

Basically they measure the trail of light things leave behind as they move along. That's about all I know of it, but typing 'Redshift' into Google or Wikipedia might (I say 'might') tell more.

Being unusual even amongst Christians in my status as a Young-Earth Creationist I don't believe that the Universe is a fragment of that age, but that's just me. I did find it very fascinating, especially the bit where they compared the USA to various planets and moons. I did rather feel that the Milky Way got somewhat shoved aside in favour of less local galaxies, however.
It's a shame they didn't go all sci-fi and loop the cycle from top-to-bottom, making out that our entire universe is a mere neutrino in the eye of another dimention... ooh, ahh...

It was difficult to navigate without constant finger-holding and pixel-precision mouse control, but otherwise interesting.

Arrow keys.
Though actually I agree; it'd've been nice to have those little arrow thingies at either end of the scrollbar for you to use.

I want a mouse with a DPI switch (for quickly swapping between ~3 DPI settings) especially for situations such as those.

how do you not know how to use punctuation?

Old. But interesting even if you have seen it before.

The Universe and the game.

the full size of the universe is only estimated so even if they know the rate of expansion and work it backwards they can't know how long ago the universe wasn't anything

Cosmic Microwave Background Radiation

You know the blackness in the sky? You know, that bit behind all the twinkly things? That is what the early universe looked like. Not just like, it is the early universe.

By "early" I mean around the age of one second. Younger, even.

Back then, the universe was thick with particle soup, and was completely opaque. No light could penetrate far. Indeed, even it it could, there was nothing to really illuminate, and the only source was almost everything. It was fucking hot. We know this from both observations from various particle accelerators and predictions made by mathematics (which are then confirmed by those accelerators and our astronomical observations).

The bleeding hairy edge of modern physics is now entirely beyond the human senses. We need technological senses to detect what is invisible to us, and mathematics to quantify, qualify and understand what we find. You can't do experimental physics research on your desk any more, unless your desk is an elecotromagnetic ring fifteen miles radius and buried underground.

Anyway, it didn't take long for the universe to become very, very large. About one second again (a period called "Inflation" which is much more impressive than the Big Bang, aka damp squib. Inflation theory explains what didn't quite fit in the standard Big Bang expansion model.

So, light itself takes time to get anywhere. It is fastest in a vacuum (though some recent experiments are supposed to have somehow exceeded this, but there is a lot more work to do before we can even discuss that possibility. They may be wrong). In a perfect vacuum, ie space, which is close enough, it takes on second for light to travel 300,000 kilometers, or 186,000 miles. In a year, it travels one light year.

The black curtain at the edge of the visible universe is approximately 13.7 billion light years away. The universe is calculated to be 13.7 billion years old based on various methods and measurements. Coincidence? Not at all. Although the universe extends beyond the visible edge, the light from the stars beyond is still en route. The universe has not existed long enough for the light from the stars beyond to have reached us yet. This black curtain, which isn't an actual thing, is receding from us at light speed, as the visible universe, a sphere 13.7 billion light years in radius centred on the observer, expands. Incidentally, the stars that are revealed this way (not that we have the lifespan to measure their appearance) no longer exist, a trait shared with many of the stars in the sky. They have died, but their light from their life still travels through space. Eventually the flash of their novas catch up.

Finally, although the visible universe appears 13.7 billion light years in radius, it is actually about 98 billion light years in radius. This is because the universe is still expanding, but the light from objects from when they were closer is still travelling toward us. The light from the farthest objects is redshifted. Light from objects moving way is red shifted due to the Doppler Effect, ie its wavelengths extended so that they appear redder (and advancing towards invisible wavelengths). But the redshift from the most farthest objects is actually because the fabric of space itself is expanding, which stretches out the light as it travels through it. This effect is only noticeable with the most distant objects, close ones, up to galaxies even, are kept closer because of the attraction of their gravity.

But the rate of the expansion of the universe is increasing, mysteriously. It shouldn't be, the mass within the universe should slow it down. The cause is unknown, the placeholder name for it is "dark energy". It is a meaningless term, it could as well have been called "Derrick". but it does mean that eventually the galaxies themselves will be carried beyond the expanding veil of the visible universe and be lost to us. The astronomers of future generations (of some other species millions or billions of years down the line) will see no galaxies or any really interesting phenomena that has our own scratching their heads. Without the availability of this data they will never unlock of the mysteries of the universe.

We should count ourselves lucky that we live in (or that our species evolved in) a time when it is at least possible to discover the origin and nature of the universe. We should not squander that.

So seek out your local space program and/or observatory and give them all your money! Clock's ticking people!

EDIT: sorry, that was a cuntish thing I just said there.

What I meant was: we don't actually know this any more than dis-proven astronomical theorists of the past.

It's a theory based on a series of apparent facts which themselves are based on observations - which are all we can base it on, and therefore we will never know, we can only theorise.

EDIT 2: read it now.

If the rate of expansion is increasing, then it is not constant. If it is not constant, how can we say what speed it was expanding at 13.7 billion years ago?

I don't even believe the universe is finite (though I don't believe it isn't, either), and in the same way I do not believe in the Big Bang theory.

Explain to me how can know for sure that the universe is getting bigger and that it was a single point that blew up.


BTW, Terry Pratchett's Big Bang theory is cooler

I recommend that you go read The Universe : a Biography by John Gribbin. It's an excellent book that explains the origin of the universe in simple (comparitively speaking) terms. It's also good as an explanation of the concept of theories and models and the process of testing them.

But how does he know he's correct?

Firstly, the rate is constant, we can observe this. And the effect of the rate increase is very small in the earlier stages anyway.


And technically, no, we can't know that it is true. But if you objectively hold that standard of certainty, then we don't know anything at all about anything. Uncertainty is a part of science, from the precision of the tools you use to measure things, to the fundamentally necessary principle of falsifiability, in which you list things that, were they found to be true, would prove a theory wrong. Looking for those things and/or experimentally trying to bring them about is how you test ideas in science.

Making it possible to know that you are wrong when you are, which is more important than anything in science (and stops it from turning into religion) comes at the expense of absolute certainty, which was always a false economy anyway. And yet the fruits of science are no less wonderful or functional for it. In fact they are more so.

For example, we know that Newton was wrong. His ideas still work in day to day life and for simple obervations, and in those circumstances are indeed used, because they are simpler and more than sufficient. On grand scales of size and speed, Einstein's relativity is the only thing that works. And relativity can get you right up to singularities, but can't actually get you there (singularities are when the numbers you put into Einstein's formulas quite literally result in dividing by zero. It actually does). We will need something else to cover singularities (and combine relativity with quantum mechanics).

The killer is that any new theory not only has to explain the evidence that disproved the old one, but all of the old evidence as well.

Just go read the book, Ench. It explains the answers to all your questions, even the ones you haven't thought of yet.

That first bit is inflation. I already explained that. And I said that the rate of the increase in rate is constant, or seems to be.

You've done quadratics, right?

Note the sudden expansion at the end. How is that constant?

Rate, RATE! Rate of the change of rate! It's positive feedback. the universe grows larger, matter becomes more space, the effect of their collective gravity weakens and is less able to slow expansion like we might otherwise expect. Rinse and repeat.

Tell me you done quadratics. That would make it so much easier to visualise.

So what does Dark Energy do?

As I already said, dark energy (or Derrick) is just a place holder name for something we don't understand. It's not necessarily dark nor energy, and is probably neither. It probably doesn't respond to the name "Derrick" either. It represents a major gap in our understanding that we are working on. Some people are working on finding out what is causing the rate of expansion to increase that we can use to adjust our models, and others are working on an entirely new model that doesn't have that problem.

Both are very difficult, and any breakthrough will probably come out of the blue from an unexpected source. They usually do.

1) we assume the rate of expansion is constant because it appears so

2) oops, the rate of expansion actually changed a billion years ago, there must be a cause for that


Rather than postulating wildly, maybe they could realise that if evidence which the theory was built on suddenly appears to not actually work for that theory, then maybe the theory was wrong.

The name Dark Energy was chosen because it sounds cool, thus making people more inclined to believe it. If they had called it Derrick, you probably wouldn't have even mentioned it. Or maybe you would have, because it would be funny.

1. Jesus, the rate of the rate! Expansion is speeding up. The rate of expansion appears to be increasing at a constant rate! We don't know why, buy it is, and I challenge any other institution to ever admit it is ignorant or could be wrong about anything. Regardless of the dark energy expansion rate, it fits well within the precision values of our estimation of the age of the universe (13.75 ± 0.11 billion years)

2. The force of dark energy expansion begins to exceed the force of gravity that would slow it. We can account for this.

The name "dark energy" was chosen because of "dark matter". Dark matter is another thing we don't understand, though we understand it better than dark energy. Matter, which generally has mass, has a gravitational signature. All masses have gravity, even ants, but gravity is the weakest of the four fundamental forces so only has en effect when there is a lot of mass in one place. We can observe the effect of that gravitational signature on the universe.

But wait: all the matter in the universe that we can account for (and it's quite easy to account for it: much of it is very, very bright) can only be producing 20% of this signature. What about the other 80%? There are two possibilities: that our models are wrong (and it's not as simple as that when they make such accurate predictions), or if they are right, then they predict the existance of something else in the universe that we don't know about. Both avenues are being explored, but without answers to either, our current models remain the most useful. We call it "dark" because we can't see it, and "matter" because the very clue that we inferred it from was a behaviour that matter is known to have. A more proper name is also goes by is "cold dark matter". Neither emitting nor reflective heat or light.

The term "dark energy" just follows this impromptu convention. Normal matter and dark matter account for only 26% of the mass-energy density of the universe, based on, among other things, data from the Wilkinson Microwave Anisotropy Probe. The WMAP measures the remnant radial heat of the Big Bang itself: we can actually see it.

WE JUST NEED TO FIND THE MASS OF A NEUTRINO DAMMIT