[Closed] How do "we" "know" how old the universe is?

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Don't they (the clever people) look at the speed that the universe is expanding and then work that backwards to the point where it, erm, wasn't expanding.

You know how if you heat soemthign up if glows red, then white etc

Well thats because the more energy something emits the higher the frequency of the radiation from it, so it glows infra red , then red, white, blueish (think car hedlamps, projectors etc), then eventualy microwaves, gamma rays etc.

Now assuming that the start was infinate energy, you find the background 'noise' in the universe with a radio telescope, measure its wavelelngth, and you know how much energy is left, and form that you can infer how old/big the universe is.

Dunno. But I know a a man who does.

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😀 @ oldgit...the concept of infinity just gives me a headache.

There's a label with cleaning details on the south west corner. If you scan the barcode it should give you a date of manufacture.

😉

And if the universe started from a single point and is expanding into infinite space - how is Andromeda going to collide with the Milky Way?

These are questions that arise from my dream last night.

As is - if we can see 13 billion odd years in one direction, how far can we see in the other direction?

Aren't there also other clues to the other age, such at the abundance of heavy elements which are formed when stars die. These are quite important for life too, so theres a theory life (similar to ours) couldn't have occurred much earlier.

wooobob - Member
Dunno. But I know a a man who does.

me too 😉

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How do "we" "know" how old the universe is

"we" don't categorically know, but we can make educated calculations, which'll become more accurate over time as our knowledge & understanding develops

There are quite a few ways that all corroborate each other loosely.

One is to use red-shift. Because of the way the universe is expanding (like a balloon being inflated) the further away something is from any point, the faster it is moving away. So the more its light is red-shifted (due to the Doppler effect). We can check this for closer objects by measuring their distance another way, which involves measuring their apparent position 6 months apart when we are on the opposite side of the sun and triangulating.

Measure the red-shift, measure the distance. Some stuff is x billion light years away, but nothing can travel faster than light, so the (current) universe cannot be any older than x billion years.

As for galaxies crashing into ours - let me swap the balloon analogy for a slightly more complicated one. Imagine a conical bowl. If you fill it with water from a hole in the bottom, the surface area of the water gets bigger as you fill, of course. Now as it's filling, put some.. I dunno.. polystyrene beads on the surface, and give it a swirl. On the whole, the surface is still expanding and most of the beads are getting further apart, but locally as the water swirls some of the beads will inevitably move towards each other and some will end up sticking together (in this case because of the water's surface tension, but in the case of galaxies gravity creates a similar effect but over a longer range).

"but nothing can travel faster than light" nothing that we are aware of.If the universe is infinite light speed would be pretty slow.

Speed of light cant be used as a constant in that context though. There are a few theories that the speed of light has changed over the life of the universe. The main reasoning for this it's the universe is bigger than it should be

"but nothing can travel faster than light" nothing that we are aware of

Well yes but if something could then all the rules we've been verifying all these years would be completely wrong. Possible but not particularly likely 🙂

Re the speed of light changing. The speed of light in a vacuum is (traditionally) contstant, but the early universe couldn't really be described as a vacuum could it?

Plus gravity seems to operate faster than light, maybe instantly, nobody knows yet

Edit, nobody actually seems to know what gravity is!

Also quantum entanglement, perhaps.

I still want to know [url= http://www.singletrackworld.com/forum/topic/is-the-universe-hollow ]if the universe is hollow[/url]. 🙁

Thats the thing with science, no absolutes. Infinite possibilites in an infinite universe.

indeed, which could turn out to be another form of gravity, or vice versa

the universe is bigger than it should be

what's the recommended size for a universe?
is there an international standard?
(just in case I ever get round to creating one)

Plus the direction of light can be changed by the mass of quite big objects. And naughty black holes will even steal it and not give it back. Or tell you where it has been hidden! Naughty!

TFM are you a real scientist or the armchair variety? 🙂

the universe is expanding (like a balloon being inflated)

I thought the universe was doughnut shaped?
Or possible saddle shaped?

If it's balloon shapes, is it one of those long sausage-shaped ones, because that would mean one end is moving away from the other a lot faster than the sides are moving awat from each other.

Christ - I won't sleep tonight.

Where's the Anadin?

this subject is far too demanding for my peanut brain, especially on a friday - lets talk about beer please...

in an infinite universe

so now the universe is infinite?

in which case trying to measure it's size is stupid and pointless ...

TheFunkyMonkey - Member

Plus gravity seems to operate faster than light, maybe instantly, nobody knows yet

That's not true.

What I don't understand is this:

EDIT I think I just realised my mistake, as you were 🙂

so now the universe is infinite?

in which case trying to measure it's size is stupid and pointless ...

We did this yesterday. The maths boffins maintained that there were different sizes of inifinity..

like infinity and infinity+1 ?

🙄

sounds like someone's making things up to explain something they've no idea about

How do you measure the speed of gravity ?
You can switch on a light source and measure how long it takes the light to get somewhere.
How do you instantly switch on a gravity source ?

So if space is expanding then surely all points are moving away from each other

All explained in full

MidlandTrailquestsGraham - Member

How do you measure the speed of gravity ?
You can switch on a light source and measure how long it takes the light to get somewhere.
How do you instantly switch on a gravity source ?

I don't know but I think it would invalidate the general theory of relativity if it did so.

mol, you answered that question yourself earlier! space is expanding, but gravity causes objects locally* to be attracted to each other.

* on a universal scale

EDIT: ignore the above, mol has edited his post

molgrips, as the light source is 'moving away' from us and the speed of light is constant, the wavelength increases and shifts to the red end of the spectrum, hence red shift.

Blue shift is due to the wavelength decreasing and moving towards the 'blue' end of the spectrum.

(I think...)

Just to be annoying, the universe is expanding faster than the speed of light. So we may never get there.

Just to be annoying, the universe is expanding faster than the speed of light. So we may never get there

To be a pedant, current favoured theory is that at some point at the beginning, it did expand faster than the current speed of light but it is not expanding that fast anymore. Either way this is correct:

So we may never get there.

But what if the universe were on a massive conveyor belt.......?

Why not just cut in half and then count the rings?

does anybody know what the universe is expanding into?

Itself.

Why not just cut in half and then count the rings?

or count the candles on it's cake

is there anything beyond the universe ?