**Ask a monkey a physics question thread**

[OngBonga]

Yeah, because there's not enough iphones on ebay.

I'll have an update in a month, then we'll have an idea if I'm wasting my money and time.

[MadMojoMonkey]

I get it won't sell to proper chemists, but schools looking to save a few quid on test tubes?

IDK. I'm sure in America, some idiot would protest that you probably just sold the school your meth lab. Who knows if that gains traction with other members of the PTA.
Still worth a shot to phone up any local high schools (or whatever you call them in the UK) and get in touch with their chemistry and physics teachers.

Don't offer to clean anything for them. If the person whom sold you the stuff didn't clean it, then there could be a reason. It could be that they are lazy, or it could be something else.
There's no point in volunteering extra time and effort on your end when your goal is to simply buy something at $10 and sell it at $13 (or whatever).

Why buy new stuff when they're "dirty" after their first use?

In general, you know exactly what's dirtying it and that's the key.
It's not so much that it's contaminated, it's that it's contaminated with unknown substances.

Also, there's surely a large amateur chemist market.

Maybe not just chemists. I use a fair amount of glassware in my physics demos.

My brother makes vape juice and uses chem lab equipment and glassware.

I'll clean everything first with diluted bleach then rinse thoroughly with water. That's sufficient for most applications, surely?

Please don't do that.
You have literally no idea what chemicals you're trying to clean off those items, and you don't know whether any of those chemicals will interact with the bleach.

If you find a potential buyer whom is concerned about filth, then... maybe... offer to wipe them off with a dry cloth. Even water could activate an acid and that's not likely to be a big deal, given the amounts we're expecting, but it could cause some skin irritation or damage the cloth you're using.

The biggest concern is in creating toxic vapors. Not all of the things that can harm you have a bad smell, and some of the things that smell bad have done their damage if they're concentrated enough for you to smell them.

So long as I make my £500 back within two or three months, and I still have plenty of stuff left, I'll be happy.

I hope it all works out.

[MadMojoMonkey]

Not so long ago, I bought a strip of magnesium ribbon for the sole purpose of setting it on fire.

... under water, I hope.

[Savy]

A school isn't going to buy used lab equipment off a stoner.

[OngBonga]

A school isn't going to buy used lab equipment off a stoner.

haha shall I say in my product description that I'm a stoner, or should I advise people when they make a purchase?

[OngBonga]

Please don't do that.
You have literally no idea what chemicals you're trying to clean off those items, and you don't know whether any of those chemicals will interact with the bleach.

Ok I won't. Thanks for the advise. I figured bleach would just remove anything, leaving a residue of chlorine or something, which can be washed off. I'm ok doing it outside to counter any noxious gasses. But if it isn't going to "clean" the glass, there's no point.

Let's see what state they're in when I get them. They might not need any attention. They are certainly already highly organised, it appears the school who sold them had their pupils well drilled in cleaning apparatus after use. But that's based on photos.

[OngBonga]

... under water, I hope.

Is this a thing? How do I set fire to magnesium under water, and what happens if I do?

[MadMojoMonkey]

Is this a thing? How do I set fire to magnesium under water, and what happens if I do?

There are plenty of videos on this. This one is pretty short and cuts to the demonstration quickly without a long explanation.



Periodic Videos has a video on this as well, but it's longer and goes into the details of the reaction a bit more.

[Poopadoop]

I'll clean everything first with diluted bleach then rinse thoroughly with water.

Sure, then while you're in the hospital recovering you can sell it.

[OngBonga]

I'm totally doing this once I have my own mini lab.

[Poopadoop]

IDK. I'm sure in America, some idiot would protest that you probably just sold the school your meth lab. Who knows if that gains traction with other members of the PTA.

Here too.

Private individual tries to sell llab equipment to a school; no questions asked.

[OngBonga]

Here too.

Private individual tries to sell llab equipment to a school; no questions asked.

Do you imagine me turning up at schools, unshaven, stinking of weed, asking them if they want to buy my boiling flasks and test tubes?

I'm imagining some school with dickheads for pupils, breaking test tubes all the time, trying to save a few quid by buying cheap replacements on ebay, and clicking on my shit. Then they buy it, because it'll be cheaper than anyone else is selling it in the UK.

[Poopadoop]

There are plenty of videos on this.

Are there any videos showing how to sell used lab equipment? I think that's what's really needed here.

How about a video showing how to clean it without poisoning yourself.

[Poopadoop]

Do you imagine me turning up at schools, unshaven, stinking of weed, asking them if they want to buy my boiling flasks and test tubes?

I'm imagining some school with dickheads for pupils, breaking test tubes all the time, trying to save a few quid by buying cheap replacements on ebay, and clicking on my shit. Then they buy it, because it'll be cheaper than anyone else is selling it in the UK.

Maybe there's a school that purchases things off ebay from unknown people to use in a chemistry lab with young people. But I kinda doubt it.

[OngBonga]

Maybe there's a school that purchases things off ebay from unknown people to use in a chemistry lab with young people. But I kinda doubt it.

Fuck me I bet you're a barrel of laughs in the board room.

[MadMojoMonkey]

Do you imagine me turning up at schools, unshaven, stinking of weed, asking them if they want to buy my boiling flasks and test tubes?

Well, now I am.

[Poopadoop]

Fuck me I bet you're a barrel of laughs in the board room.

Seriously you have no sensible plan for how to sell this stuff.

You think 'a school sold them to me, a different school will buy them'

Fact is, there is no way a school goes and buys chemistry kit off of ebay. Unlike you, these people have to answer to other people; they can't just do whatever they want to save a few quid. And it's not like they get to keep whatever money they save and split it amongst themselves. It just goes back into some big pot somewhere and they never see it again. Why should they take a chance on buying some contanimated-with-God-knows-what lab kit from some-guy-on-ebay who happens to have a lot of lab shit lying around, when it's not even their money they're spending to begin with.

And you talked in some other thread about people not knowing how the world works.

[OngBonga]

Seriously you have no sensible plan for how to sell this stuff.

I'm not at business plan level here, but if you're asking me if I did any research to see if I could sell this stuff and at what kind of price, then yes I did. But I can only do so much when I'm looking at photos. Have I taken a risk? Yes. Am I happy to take the risk? Yes, this looks like fun. At worst, I've got a fucking lab.

It's 500 quid, if it turns out to be a waste of time I could probably list it as an entire lot at the same price I paid for it and shift it onto another mug who thinks there's a market for it when there isn't. Except it'll be missing one of everything.

[OngBonga]

I could probably film myself blowing up a makeshift lab and rake in the youtube profits.

Assuming I survive.

[Poopadoop]

I could probably film myself blowing up a makeshift lab and rake in the youtube profits.

Assuming I survive.

You could probably get a used bomb disposal suit for a couple hundred quid.

[OngBonga]

That box of tongs is £100

[BananaStand]

I hope that lot came bundled with some bonus IQs

[MadMojoMonkey]

Ongie's YouTube channel where he gets overly excited to poorly explain some scientific shizwaz that was done using some piece of equipment.
Then he uses fireworks and DIY nonsense to destroy the equipment.

A science show that always ends with explosions and destruction?
Yes, please.

... calls in the Slow-Mo Guys to do a collab. Shows the explosion in regular time and shows ongie making some stupid mistake in frame-by-frame.


I think I'd watch that.
I think I'd watch a lot of that.

[OngBonga]

Let's take this discussion to surviva's UPDATE thread.

Someone ask mojo something sciency.

[OngBonga]

I think I'd watch that.
I think I'd watch a lot of that.

End with explosions. Yep, noted. I'd have probably come up with that idea myself, but I'll give you a shout out for it all the same.

[OngBonga]

What are these are what do they do?
My best guess... micro bubbler and micro funnel, the funnel is self explanitory but the bubbler... I guess it goes into a test tube and gives gasses a place to expand to ensure no liquid can escape.
BB01.jpgBB02.jpg

[OngBonga]

Do you know of anywhere on the web where I can get a comprehensive image bank of chemistry lab glassware? The ones I have found are pretty basic, there's quite a lot here that I'm struggling to accurately identify.

I could make a fucking awesome bong, I know that much.

edit - I'm just gonna dump a link here for future use...
https://www.thoughtco.com/chemistry-...allery-4054177

[Poopadoop]

Oh, you're still alive? Well done!

[MadMojoMonkey]

I guess it goes into a test tube and gives gasses a place to expand to ensure no liquid can escape.

IDK what either of those things is.

I think liquids don't usually escape from the top of a container, unless they're in a super-fluid phase.

[OngBonga]

Oh, you're still alive? Well done!

Haven't started cleaning stuff yet, just cataloguing.

IDK what either of those things is.

I think liquids don't usually escape from the top of a container, unless they're in a super-fluid phase.

hmm interesting. Those bungs clearly go into test tubes, but I can't find similar images by googling.

I'll keep digging, I'll find a good resource sooner or later.

[BananaStand]

Made any money yet?

[OngBonga]

Made any money yet?

Of course not. I haven't listed anything yet. However, I'm happy with what I'm finding. There's a handful of Wedgewood mortar and pestles, they're vintage and are potentially worth £25 a piece. There's hundreds of Royal Worcester fluted funnels, RW is collectable china and they probably sell for at least £10 each.

I'm not going to make a quick buck from this lot, but if by the end of the year I haven't doubled my money, I'll be surprised.

[MadMojoMonkey]

hmm interesting. Those bungs clearly go into test tubes, but I can't find similar images by googling.

I'll keep digging, I'll find a good resource sooner or later.

The shape of it reminds me of the sewer traps you see under any plumbing drain. Their purpose is to trap the stank sewer gas behind that fluid blockage that collects in the bend.

[BananaStand]

How many of these things have you personally smoked weed out of so far?

[OngBonga]

How many of these things have you personally smoked weed out of so far?

None yet, but I'm definitely going to.

[OngBonga]

The shape of it reminds me of the sewer traps you see under any plumbing drain. Their purpose is to trap the stank sewer gas behind that fluid blockage that collects in the bend.

Yeah I definitely think it's a gas trap of some sort. My thinking was if there's a vigorous reaction in a test tube releasing gas, this little thing will stop is spewing over and ensure that what comes out is only gas. But I really am just guessing, I've never seen one before. Got hundreds of the little buggers.

[OngBonga]

Mojo, are you a mathematician?

[MadMojoMonkey]

Mojo, are you a mathematician?

Not currently employed to do math, but a large portion of my job involves using math.
Professionally, I could do math for a living and I'd be good at it.

That said, I cannot force myself to be interested in raw, abstract math. If I can't see an application of the math, my brain just refuses to remember it. So in that regard, I am definitely not a mathematician.

[OngBonga]

Ok, it's just that there's this thing called Cantor's Diagonal Argument which is considered proof that there are infinitely more irrational numbers than ratioanl numbers.

I have reason to think that around 61% of all numbers are rational, and I have what seems to me a compelling proof. Bet that perks your mathematical interest.

[OngBonga]

If that fails to perk your interest, then I'll add that by "around 61%" I mean "precisely 100(6/pi^2)%"

[MadMojoMonkey]

A quick wiki check says that his argument has different interpretations, but it basically says, "Look. The counting numbers do not create a set of size which has a countable infinity. The number of counting numbers is not a countable infinity!"

But I digress, so...
What's your argument, then?

[Savy]

When I read ongs post I thought to myself that definitely isn't what cantors diaganol argument proves. It may follow on from it but it's not obvious (in my simple mind) how it follows. So I looked at wiki and Wiki says real numbers and irrational numbers have the same cardinality.

[Savy]

A quick wiki check says that his argument has different interpretations, but it basically says, "Look. The counting numbers do not create a set of size which has a countable infinity. The number of counting numbers is not a countable infinity!"

I don't follow. It says the countable numbers which are infinite you'd think would be so big everything could fit in there, ldo. Ohh shit look at all these things that don't fit in there because they are "bigger".

[MadMojoMonkey]

I don't follow. It says the countable numbers which are infinite you'd think would be so big everything could fit in there, ldo. Ohh shit look at all these things that don't fit in there because they are "bigger".

I thought is was all, if we presume some list of all counting numbers, then we make a number that is different from every element in that list in at least one digit, then we have created a "new" counting number that was not previously in our infinite set of counting numbers... ergo, the number of counting numbers is not countable.

I don't think he invoked any other things aside from counting numbers, but he had multiple arguments on this and similar topics, and maybe I wiki'd the wrong one.

[OngBonga]

You'd probably need to watch Numberphile's episode on the Infinite Orchard problem to really get the gist, but here's the crux of it.

We're going to need to plot an infinite graph, with x and y axes. The intersection of the two axes will be (0,0), and we'll plot a point at every pair of integers. Now, if we draw a line from (0,0) to (1,1), and then extend it, we'll see that what we're doing here is drawing a line through every pair of integers that has a ratio of 1:1. If we draw the lin from (0,0) to (1,2), next point we hit will be (2,4), then (3,6), and this is a different constant ratio line, this time 1:2.

It doesn't take much to conclude that what we are doing when we draw a straight line through a point is drawing a rational number line.

An irrational number line will never hit a point, it will find a way through the infinity of points without directly hitting one. If the line hits a tree, you just found a way to express that ratio in terms of integers. The pi line will go close to (22,7), closer yet to (355,113), and closer yet to even more accurate approximations.

The phi line is the most interesting one though, since it manages to maintain the furthest possible distance from a point. Phi, aka the golden ratio, is the most irrational number, because it is the least well approximated. You'll need huge denominators to approximate phi to the same accuracy as 355/113 does for pi.

Anyway, it's this that I think the Cantor diagonal theory fails to realise... that irrational numbers have different levels of irrationality, and the more irrational a number is, the rarer it is.

But here's the kicker... the guy on Numberphile pulls a number pretty much out of his arse, with no explanation, which is a shame, but he basically says the probability of taking a random line of sight and hitting a point is 6/pi^2, which is a really interesting number for reasons you might appreciate. It's the reciprical of the inverse square infinite fraction. But I digress... if that's the probabiltiy of looking at a tree in an infinite orchard, then it's the same as the probability of picking a number at random, and it's rational. So the idea that "almost all" numbers are irrational seems to me very, very wrong. Actually most numbers are rational.

Tell me where I'm being dumb!

[OngBonga]

Here's the Numberphile video...

[OngBonga]

This is a dirty quick quote from wikipedia...

As a consequence of Cantor's proof that the real numbers are uncountable and the rationals countable, it follows that almost all real numbers are irrational.

[OngBonga]

This image is off wikipedia...

The rational numbers (ℚ) are included in the real numbers (ℝ). On the other hand, they include the integers (ℤ), which in turn include the natural numbers (ℕ)

I have no idea how to calculate the ratios of ellipses, but Q looks like it could be just over half of R.

My interpretation of Cantor's argument is clearly wrong, but my calculations don't seem to be. That's worthy of a fistpump.

[Savy]

Tell me where I'm being dumb!

rational numbers are countable
https://www.homeschoolmath.net/teach...-countable.php

irrational numbers are uncountable

cantors diaganol argument literally goes against what you're trying to say it proves?

To put this as simple as possible if every rational number was in a row on the left and every irrational number was in a row on the right (from smallest to biggest) and you paired them up you would always have irrational numbers left over, so if you can push it as far as this it's definitely <50% and it may even follow that 0% of the reals are rational but probably not.

[Savy]

This image is off wikipedia...





I have no idea how to calculate the ratios of ellipses, but Q looks like it could be just over half of R.

My interpretation of Cantor's argument is clearly wrong, but my calculations don't seem to be. That's worthy of a fistpump.

Thats' like 99.9% arbitrary as fuck and means nothing.

[OngBonga]

rational numbers are countable

irrational numbers are uncountable

Yeah this "countable" and "uncountable" bollocks with regard to infinity is not really very clear to me.

[OngBonga]

Thats' like 99.9% arbitrary as fuck and means nothing.

Sure, but the infinite orchard thing isn't arbitrary, at least if he has a proof for his 6/pi^2 number.

[Savy]

Yeah this "countable" and "uncountable" bollocks with regard to infinity is not really very clear to me.

Basically if something is countable you can essentially take every element in the set and say it's the same as 1, 2, 3 etc. The link I posted shows how you can do this for rational numbers.

There are some sets where if you do this it's impossible to have every element in that set match up to 1, 2, 3 etc. There is essentially stuff left over. It's why there are infinitely more numbers between 0 and 1 than there are natural numbers.

[Savy]

Also if it's of any interest to you

http://www.ams.org/publicoutreach/fe...rc-irrational2

[OngBonga]

I do get that not all infinities are the same size, some are infinitly bigger than others. It seems crazy but it's also logical, the fractions compared to whole numbers is a perfect example that is easy to get your head around.

But "countable" and "uncountable"... I have read up on them and I just don't get it. For a start, no infinity is countable. Ok, we can list the numbers 1 to infinity if we have infinite time and infinite pen and paper, also infinite weed please so I don't get bored, and probably we can't list irrational numbers because there would be no method to ensure we got them all. Am I getting it?

Just because an infinity is "uncountable", doesn't mean it's infinitly bigger than a "countable" one. I don't see any reason why that needs to be the case.

[OngBonga]

Also if it's of any interest to you

http://www.ams.org/publicoutreach/fe...rc-irrational2

Indeed interesting, but it's weird they showed how root 2 is much more irrational than pi, without mentioning phi, the most irrational number.

[oskar]

Basically if something is countable you can essentially take every element in the set and say it's the same as 1, 2, 3 etc. The link I posted shows how you can do this for rational numbers.

There are some sets where if you do this it's impossible to have every element in that set match up to 1, 2, 3 etc. There is essentially stuff left over. It's why there are infinitely more numbers between 0 and 1 than there are natural numbers.

Is it fair to say it's one of those cases where the technical term simply means something else than the colloquial? Just because the R infinity isn't listable using the N infinity doesn't make the N one countable.

[OngBonga]

So I found out why the probability of looking at a point is 6/pi^2

That just happens to be the probability that you pick two arbitrary whole numbers at random and they are co-prime, that is they have no common denominator. That's the same as looking in a direction on our infinite orchard and seeing a point... that point we see is the first in a line, the first one being the co-prime integers, with all the hidden points behind being the same ratio and therefore not co-prime.

To demonstrate co-prime... 6 and 7 are co-prime, since the only common denominator is 1, however 6 is not prime since it's even. The point (6,7) on our graph is the first point in that line, every hidden point behind it has a common denominator... (12,14) - 2, then (18,21) - 3, then (24, 28) - 4, then (30,35) - 5 etc.

So now we know where the value 6/pi^2 comes from. It's a product of the Riemann Zeta Function.

[Savy]

Is it fair to say it's one of those cases where the technical term simply means something else than the colloquial? Just because the R infinity isn't listable using the N infinity doesn't make the N one countable.

No, N is countable in literally the exact meaning of the word. Whereas with sets like R it's literally imposisble to count all the elements.

The words that probably aren't the best are words like big. In the case of R and N it makes some sense because N is contained in R but the irrationals are also contained in R but by this measure they are the same. I think this is somewhat down to a countable infinity being so insignificant compared to uncountable ones that even though R = R/Q & Q, Q is basically nothing but that's very hand wavy nonsense.

It's all to do with mapping each element to each other.

so {a, b, c, d} has cardinality 4 which is the same as {1, 2, 3, 4} and each element of one set can be mapped to the other i.e. a to 1, b to 2 etc.

N has a smaller cardinality than R and R/Q

R has the same cardinality as R/Q because you can still (don't ask me how) map every element of R to one in R/Q.

[MadMojoMonkey]

What does the forward slash mean?
E.g. R/Q

What does that operator mean in the context of sets?

[MadMojoMonkey]

So I found out why the probability of looking at a point is 6/pi^2

That just happens to be the probability that you pick two arbitrary whole numbers at random and they are co-prime, that is they have no common denominator. That's the same as looking in a direction on our infinite orchard and seeing a point... that point we see is the first in a line, the first one being the co-prime integers, with all the hidden points behind being the same ratio and therefore not co-prime.

To demonstrate co-prime... 6 and 7 are co-prime, since the only common denominator is 1, however 6 is not prime since it's even. The point (6,7) on our graph is the first point in that line, every hidden point behind it has a common denominator... (12,14) - 2, then (18,21) - 3, then (24, 28) - 4, then (30,35) - 5 etc.

So now we know where the value 6/pi^2 comes from. It's a product of the Riemann Zeta Function.

There's a tree on every pair of whole numbers, so if we're just picking whole numbers at random, then we always look at a tree, right?

[OngBonga]

There's a tree on every pair of whole numbers, so if we're just picking whole numbers at random, then we always look at a tree, right?

You're right, but the probabilities are the same, according to what I think are reliable sources.

The probability of picking two co-prime numbers at random is 6/pi^2, and according to numberphile, that's the same as looking at a tree at random.

That can't be a coincidence?

[MadMojoMonkey]

Seems like that's just the probability that if we look in the direction of a random (x,y), where x and y are integers, that the tree we see will be at (x,y) and not some closer tree in front of it, right?

[OngBonga]

Seems like that's just the probability that if we look in the direction of a random (x,y), where x and y are integers, that the tree we see will be at (x,y) and not some closer tree in front of it, right?

Yeah. But it's also the probability that we see a tree if we look in a random direction on the infinite orchard. That's according to numberphile, I'm yet to understand where that number comes from.

Interesting, the reciprocal, ie pi^2/6, is the product of the infinite fraction...
1+ ( 1/4 + ( 1/9 + ( 1/16 + ( 1/25...

Inverse square.

So that means if we put a light source on every point in our orchard, and assume that every light source is equal, and the combined light on a line is additive, then the total brightness we see along a line from (0,0) is pi^2/6 times the brightness of the first light we hit.

Again, it can't be a coincidence. I'd love to understand the connection here.

[Savy]

What does the forward slash mean?
E.g. R/Q

What does that operator mean in the context of sets?

R is reals, Q is rastionals, R/Q is reals not including rationals i.e. irrationals.

[MadMojoMonkey]

R is reals, Q is rastionals, R/Q is reals not including rationals i.e. irrationals.

Thanks. I've been trying to understand group theory again, and this notation comes up a lot, but I didn't know what it meant.

Wikipedia is terrible for never defining the notation on a math page.

[MadMojoMonkey]

R is reals, Q is rastionals, R/Q is reals not including rationals i.e. irrationals.

This is the same thing, but in slightly more formal language, right?

N/Q reads "N modulo Q" and isn't "really" N - Q, so much as it's Q is a proper subgroup of N, and thus partitions N such that all 3 of N, Q and N/Q are groups, but N/Q is not a proper group, because it lacks the identity, which is included in Q, since it is a proper group.

(Crap... I didn't mention the operation. Is it assumed that it's the same operation for all mentioned groups? Or am I really talking about sets, here?)

I'm trying to understand this.

Cosets are still a bit confusing.

[Savy]

They are sets not necessarily groups. A set is just a collection of elements a group is a set which has to strike some criteria which I can't fully remember but as you said identity, inverse and things of that nature. One of the things it requires is an operation though which none of the sets we are talking about have unless you are being specific i.e. r,+ (reals and addition).

N/Q isn't a thing I don't think as that would be the naturals without the rationals which rather than being empty I think just doesn't make sense.

It's been 5 years since I've done anything involving groups though so it's all a bit patchy.

[MadMojoMonkey]

They are sets not necessarily groups.

Thanks. I kinda caught that after I posted, and did a ninja edit, but having my suspicion confirmed is helpful.

A set is just a collection of elements a group is a set which has to strike some criteria which I can't fully remember but as you said identity, inverse and things of that nature. One of the things it requires is an operation though which none of the sets we are talking about have unless you are being specific i.e. r,+ (reals and addition).

A group is a set with an operator that meets these criteria:
Completeness - Given any 2 elements of the group, a, and b, then a b = c, where c is also an element of the group, and is the operator is associated with that group.

Associativity - For any 3 elements of the group, a, b, and c,
(a b) c = a (b c).

Identity element - For any element of the group, a, there must be an element in the group such that
a e = e a = a. This e is the identity element.

Inverses - For any element of the group, a, there must be an element in the group such that
a a_inv = a_inv a = e.

N/Q isn't a thing I don't think as that would be the naturals without the rationals which rather than being empty I think just doesn't make sense.

Crap. I meant, and was thinking, R/Q in the above post.
Oops.

[Savy]

My favourite thing about groups is the generic name for the operator is blob.

[MadMojoMonkey]

After I posted about not understanding the symbols, it allowed me to pinpoint my trouble and refine my google searches to find a bunch of links where the symbols are defined. It's made a huge difference in my ability to understand the theory.

I'm still confused by the "morphism" classes and, as I said, cosets.

I've read over a proof that N4/N2~=N2, where ~= means "is isomorphic to," about a dozen times, with multiple examples, and I'm still probably not able to recreate the argument myself, from scratch.

It's nice to be struggling with a big concept again. The little engineering problems that crop up on a daily basis are fun to solve, but not really that challenging for me.

[CoccoBill]

When taking a shower, why does the shower curtain sneak up and attach itself to your butt?

[MadMojoMonkey]

Bernoulli's Principle
Simply stated - the greater the velocity of a flowing fluid, the lower the pressure.
In this case, the fluid is the air in the bathroom/shower.

The downward flow of water has an effect of dragging a downward air flow, which induces a net flow of air as well as turbulence.
The net flow inside the shower is greater than outside, so the pressure is slightly lower in the shower than in the rest of the room.
This induces a slight pressure difference on the inside and outside of the shower curtain, pushing it slightly inward.

Then if it touches you, it tends to stick because you're all wet and between capillary action and surface tension and the low mass density of a shower curtain... it sticks.

[OngBonga]

Why is space expanding?

[MadMojoMonkey]

??? for about 10^-30 s, then universe.. expanding 'cause... iunno. Big Bang seems like a fine, if not too creative, name. We really don't understand the mechanism of inflation that happened right at the very, very berry flavored beginning. That didn't last too long, though, whatever that means in the redonkulously relativistic environment that was the entire universe. We have models that seem good-ish, but nothing experimentally confirmed that's older than the Cosmic Microwave Backround (CMB), AFAIK.

CMB happened after atoms congealed, not just the first particles, but stable Hydrogen. It's a unique signature that electrons couldn't get to their ground state without being annihilated by the ambient energy, then they could. That transition where all those electrons could suddenly jump to ground left a flash of light that is still imprinted on the distant sky.

We have no observations I know of that pre-date that event.