Interesting conversation.....

[roadrash]

Wrong, wrong, wrong!

The correct answer to this question is "What do you think I am, a blaaady astronomer?!" ...

No, we think your ..... wonnie pickewing

 

[ClichéGuevara]

A documentary a bit back started discussing things that were infinitely small.

I recognised the individual words they used when they explained it, but linked together they may as well have been Chinese.

 

[Andy_R]

Just stick him in front of Wonders of the Universe... that'll keep him quiet for at least 4 hours, after which, his skull will be filled with even more unanswerable questions

If I left him alone infront of the TV for four hours, he'd have the back off it and be salvaging units to use with his Raspberry Pi

 

[oldfatfool]

If I left him alone infront of the TV for four hours, he'd have the back off it and be salvaging units to use with his Raspberry Pi

I like pie, is it a Mary Berry recipe he uses?

 

[HertzvanRental]

Take the infinate number x, logically there must also be -x, negative infinity. This can be represented on number line joined to form a circle with 0 at 12 'o' clock and + and - infinity joined at 6 'o' clock. This 2d circle can represent an axis through the universe. As infinity is always x+1 the circle like the universe is ever expanding.

Is the answer n+1?

 

[oldfatfool]

Is the answer n+1?

That's bikes, but same principle.

 

[ColinJ]

No, we think your ..... wonnie pickewing

Wouldn't be a bit annoying and embarrassing now if your name actually were Ronnie Pickering (a different one!) ...?

 

[Tim Hall]

Klein Bottle ...... That will fool him

Shaun

My daughter knitted me a Klein bottle hat. I look rather dashing in it.

 

[midlife]

Hilbert's Paradox all over again ....

https://en.m.wikipedia.org/wiki/Hilbert's_paradox_of_the_Grand_Hotel

Shaun

 

[marinyork]

It's more on infinity, but this classic modern horizon episode is well worth a watch for your son. If anyone thinks it is a push over it features Ronald Graham himself, Gregory Chaitin, Max Tegmark and Peter Cameron.

http://www.bbc.co.uk/iplayer/episode/b00qszch/horizon-20092010-12-to-infinity-and-beyond

 

[Profpointy]

ar the risk lowering the tone, with serious answers there are at least two different things.

1 - is space infite - maybe / maybe not and anyway does depend somewhat on what the question means exaclty

2 If space is finite - is it bounded ? This is the essence of the lad's question. The usual analogy is to look at a two dimensional space - a flat plane - infinite and unbounded, a dinner plate ', finite and bounded - and the ineresting one - surface of a sphere - finite, but unbounded. Any of these can be expanding or contracting - think of stretching the surface. The surface of a sphere is mathematically a 2 dimensional thing. 3 dimensional spaces can be considered in the same way, albeit harded to visualise

Back to infinite question - the "observable" universe is finite as light / influences can only have travelled a certain distance (to us) since the big bang. Thus light from anything more than13 billion light years away hasn't had time to reach us yet. Further away things are receding faster so above some distance they are receding so fast that the light can't ever get to us. "receding" is (I think?) the wrong word as the space itself is stretching rather than things whizzing away through space (which can't be faster than light?) - A better or deeper explanaion is beyond me as I only half understand it.

Further away is outside ( now and forever) the observable universe so it is debatable whether it "counts" as part of the universe - and it may or may not be infinite.

The lad is asking great questions - get holim Malcolm Longair's "Our evolving universe" - suitable for the lay person, but still really solid and enjoyable. I apid fullnprice but was onky a couple of quid on amazon when I last looked

 

[marinyork]

At the risk lowering the tone, with serious answers there are at least two different things.

2 If space is finite - is it bounded ? This is the essence of the lad's question. The usual analogy is to look at a two dimensional space - a flat plane - infinite and unbounded, a dinner plate ', finite and bounded - and the ineresting one - surface of a sphere - finite, but unbounded. Any of these can be expanding or contracting - think of stretching the surface. The surface of a sphere is mathematically a 2 dimensional thing. 3 dimensional spaces can be considered in the same way, albeit harded to visualise

It's true, but most literature written by Physicists and cosmologists instead of the sums people talks about the different idea of Open/Closed and this is often how it will appear on serious tv or internet discussions.

There was a great horizon on the shape of the universe a few years ago, but it appears to not be on the archive available so I put the other one up instead.

 

[mjr]

So, my 12 year old son has just posed an interesting question....how can the universe be infinite if it is expanding? Answers on a postcard please, as I want to shut him up about it!

There are an infinite number of infinities of different sizes, as in the hotel @midlife mentions. The infinite universe is simply expanding into a space of a bigger infinity.

If he thinks that's difficult to understand, wait until he gets into women.

Fnarr!

 

[stephec]

"Because I'm your dad and I said so that's why," should cover it.

 

[Profpointy]

There are an infinite number of infinities of different sizes, as in the hotel @midlife mentions. The infinite universe is simply expanding into a space of a bigger infinity.


Fnarr!

sorry to be picky, but the different sizes of infities is a very very different matter


EDIT - I think so anyway