size of the universe

[munka]

I did quantum physics in Uni for 3 units as part of my engineering degree. So I can spell the word particle and have a rough concept of how little I know. But after constructing a second sentence on the subject I generally run out of steam.

However, lately and mostly inspired by the Higgs Boson discovery, I have been reading a bit more, and while I drifted way off topic I hit a very confused moment.

Look at these 3 points (sorrry I'll quote Wikipedia for consistency but have verified this in other sources):

Age of the universe is 13.75 billion years http://en.wikipedia.org/wiki/Age_of_the_universe
Universe started as a singularity (ie taking up a single point in space) http://en.wikipedia.org/wiki/Big_Bang
The visible part of the universe (to us) is 46 billlion light years wide. http://en.wikipedia.org/wiki/Universe

So take the common (most likely incorrect) human perception that we are center of the universe. Start at that single point and ignoring relativity for the moment matter is spread out at the speed of light in all directions. The biggest I can see the universe getting is 27.5 billion light years.

Even going one step further, if we can see 46 billion light years away, but nothing was there before the big bang, how did i possibly get to us already?

One of those figures isn't adding up for me.

So where do the other 18.5 billion (probably much more) years come from.

[shift]

The universe expanded at (much) greater than the speed of light immediately after the big bang.

[Dr1fty]

/end thread........

[EuroSlave]

Originally Posted by shift

The universe expanded at (much) greater than the speed of light immediately after the big bang.

Can you explain this for the science illiterates here?

[DaveHimself]

if 10 people al start at one point then move away from that point equally for 1 day, if you as one point move back it'll take one day to reach that original point but if you want to talk to the person that was opposite you then you will have to travel another day plus the day you spent travelling back to the point then the extra distance they were still travelling while you were making your way to them.


the universe expanded exponentially in all directions, so you have to add up your distance plus their distance travelled x + y = lots of numbers

[Hyram]

The Hitch Hiker's Guide To The Galaxy kicks off with an introduction to the size of the universe.

"Space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. Listen ..." and so on.

To be fair though, when confronted by the sheer enormity of the distances between the stars, better minds than the one responsible for the Guide's introduction have faltered.

Even light, which travels so fast that it takes most races thousands of years to realize that it travels at all, takes time to journey between the stars. It takes eight minutes to journey from the star Sol to the place where the Earth used to be, and four years more to arrive at Sol's nearest stellar neighbor, Alpha Proxima.

The simple truth is that interstellar distances will not fit into the human imagination.

-- Douglas Adams

[hlokk]

Ah, this ol chesnut.

The universe is 13.75 billion years old.
It is 46.5 billion light years to the edge of the observable universe. (This is called the comoving distance btw)
This makes the observable universe a sphere 93 billion light years in diameter.
(The observable universe is the universe where light has been able to reach us. The whole universe is almost certainly a lot larger than this... possibly infinite).

How is this possible? As previously mentioned, its because the universe is expanding. Simply multiplying time by speed does not work if the system is moving (it will depend what reference you use).

So as a simple answer: Imagine a person walking away from you and they put a note on a electric car that drives towards you at a constant speed. By the time the car gets to you, the person is further away than when they sent it. The car covers less distance (in its or your timeframe) than that person is now further away from you.


However, for a bit more accuracy: when the universe expands, it was not like a hand grenade that exploded, its more like a pudding expanding in the oven, or a piece of rubber being stretched.

As the universe expands, on the large scale all points get "expanded" away from each other. So, lets consider it in 1D and use an elastic band. If the elastic band expands at say 10% per second, then in 1 second, something 1m away will then be 1.1m away, but something 1km away will be 1.1km away. So relative to you, one is moving 0.1m/s and the other is moving 100m/s. However, at that 1.1km point, something 1m either side of it will only be moving 0.1m/s relative to it.

So imagine this constantly stretching rubbing band. We mark one point and consider it the centre. Then we have another spot (say 1m from us) that sends a message via an ant.
As the ant travels, the ground is stretching under its feet. After the ant has traveled say 13.7 seconds, it reaches us. To the ant, it has covered 13.7 seconds at a constant speed over the rubber band surface(analgous to the speed of light). However, because the elastic band has been stretching while the ant is moving, that 1m point the light originated from might now be several meters away.

If its expanding at any rate (linear or exponential), by the time the light gets to you it will always be futher away than the distance*time.


http://en.wikipedia.org/wiki/Observable_universe

http://www.atlasoftheuniverse.com/bigbang.html

http://www.atlasoftheuniverse.com/redshift.html

[spludgey]

Originally Posted by hlokk

*Informative post*

All very true, but this all means that the universe is larger, so therefore the matter that's out there would have had to have travelled faster than light still.

[|guanA]

You need to watch this, it will answer all your questions:

It's pretty much exactly what hlokk said, but in a very easy to understand way complete with charts.

http://www.youtube.com/watch?v=7ImvlS8PLIo

[Shepete]

No, that's all bullshit.
This is the truth.

http://www.youtube.com/watch?v=buqtdpuZxvk

Dam I wish I knew how to link a film clip

[War1910]

Originally Posted by Shepete

No, that's all bullshit.
This is the truth.

http://www.youtube.com/watch?v=buqtdpuZxvk

Dam I wish I knew how to link a film clip

put the 'buqtdpuZxv' between [ YOUTUBE ] [ /YOUTUBE ] tags:

[ YOUTUBE]buqtdpuZxv[ /YOUTUBE] =

[hlokk]

Originally Posted by spludgey

All very true, but this all means that the universe is larger, so therefore the matter that's out there would have had to have travelled faster than light still.

No. The distance the light has travelled in the lights reference frame is still 13.7 billion light years. Imagine it from the point of view of the ant. The ant travels for 13.7 seconds and 1m/s. If the ant had a little odometer, it would say it covered 13.7m in those 13.7 seconds. The ground is stretching under the ants feet, but because the ant is effectively a point, the ant can still measure "speed over ground" correctly.

By the time the ant gets to you, the point it started from is now 46m away. The sum total distance the ant traveled is 13.7m, and the ant started say 1m away from you (or whatever the actual figure works out for the expansion rate).
If you were to pause the universe now and stop it expanding. It would take 46 billion years for light to get to the edge of the observable universe (or rather where it currently is). Because the universe is expanding, a light ray will never reach something that is now 46 billion light years away though.


Take "I" as the ant. "B" as the origin, "A" as us.

A.....|B (B at say 1)
A....|...B
A...|.......B
A..|.............B
A.|......................B
A|....................................B (B at 46)

So if we sum the dots the ant travelled:
A|............... (Length = 13.7)

Notice how the distance the ant (light) travelled is less than the distance from A to B now (the comoving distance, 46 billion light years).

[munka]

Originally Posted by hlokk

No. The distance the light has travelled in the lights reference frame is still 13.7 billion light years. Imagine it from the point of view of the ant. The ant travels for 13.7 seconds and 1m/s. If the ant had a little odometer, it would say it covered 13.7m in those 13.7 seconds. The ground is stretching under the ants feet, but because the ant is effectively a point, the ant can still measure "speed over ground" correctly.

By the time the ant gets to you, the point it started from is now 46m away. The sum total distance the ant traveled is 13.7m, and the ant started say 1m away from you (or whatever the actual figure works out for the expansion rate).
If you were to pause the universe now and stop it expanding. It would take 46 billion years for light to get to the edge of the observable universe (or rather where it currently is). Because the universe is expanding, a light ray will never reach something that is now 46 billion light years away though.


Take "I" as the ant. "B" as the origin, "A" as us.

A.....|B (B at say 1)
A....|...B
A...|.......B
A..|.............B
A.|......................B
A|....................................B (B at 46)

So if we sum the dots the ant travelled:
A|............... (Length = 13.7)

Notice how the distance the ant (light) travelled is less than the distance from A to B now (the comoving distance, 46 billion light years).

You've reverted to Newtonian physics so it still falls apart. The photon (ant) in question you refer to has still travelled 46 billion light years away from B in 13.7 billion years in its frame of reference.

Also 13.7 billion years ago it wasn't 13.7 billion light years away (if the universe started as a singularity). Of course I'm bounding the early days of the universe by current day physics which may be my biggest downfall but no matter what I don't understand it!

[munka]

Originally Posted by shift

The universe expanded at (much) greater than the speed of light immediately after the big bang.

Ok this is the best explanation, where do you get that from? And how can we see further than the start of time?

[ikonz0r]

Yeh I've always wondered this too... I thought nothing could travel faster than the speed of light? Expansion = objects moving further apart.. objects moving faster than light? I don't really understand physics like some of you folk though..