Science Q&A: Ask questions, and answer them answered by the community.

[xXGeckoXx]

I was thinking it might be fun to do a science Q&A with the community. Ask questions and and read questions, if you know the answer to one, give it. Let's see what we don't know and what we can learn.

RULES:

SOURCES, SOURCES, SOURCES. Give sources.

Acceptable sources include: Reputable articles, Research papers, Wikipedia (on non-speculative topics), Reddit /r/askscience, Being an actual godamn scientist (time to shine).

Unacceptable sources: Pulp shit (cracked, most newspapers etc...).

Challenging sources is acceptable, it is the duty of the person answering the question to provide adequate evidence.

Try to keep speculation at a minimum:

It's okay to muse about difficulty questions but the best way to do so is in the form of the question.

If you are unsure instead of saying :"Well I think it's something to do with quantum physics."

Say "I wonder if it is something to do with quantum physics?"

This leaves space for people who know the stuff to join in as well as clarifying that you don't mean it as fact.

NO QUESTION IS STUPID (within reason):

Don't be embarrassed if you think your question is too simple, it most likely is not. Worst thing you will be referred to the wiki page and the answer will be in the first sentence and you will know more science.

I think I'll start with a question I already know a bit about:

Does the universe expand in all directions at the same rate?

 

[xXGeckoXx]

snip

You want us to post questions, eh?

How can we detect background radiation if it travels at the speed of light and originated form the big bang? I would assume it would be "past us" by now.

Holy shit you are good this made me think. Thinking of the big bang as having an origin point is not correct due to the shape of space, it is wrong to think of a center point, for this reason cosmic background radiation has no discernible source (http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation).

Edit: Yeah it would be great if someone could expand here.

More about the fact that there is no centre of the universe: http://math.ucr.edu/home/baez/physics/Relativity/GR/centre.html

 

[SckizoBoy]

FFS why must questions always be physics?!

Someone ask something about synthetic chemistry/botany...(!)

Question: best conditions for the Ireland-Claisen rearrangement, arrow-pushing and workup methodology, please...

 

[xXGeckoXx]

FFS why must questions always be physics?!

Someone ask something about synthetic chemistry/botany...(!)

Question: best conditions for the Ireland-Claisen rearrangement, arrow-pushing and workup methodology, please...

No reason why. Either way next question is in. I'll ask a physics/chem question (not really chem).

Optically active substances take polarized light and change it's plane of polarization. Why is the effect cumulative when shining polarized light through a volume of the substance (i.e. why are the changes in polarization different when you shine the light through different concentrations or volumes of the material). Does each molecule of the substance rotate it by the same amount and so the more you have the greater the overall rotation?

Off topic: I am going into chemistry in university but I am also interested in physics. I just find it easier to ask questions in physics or I end up in questions like the one you asked, ten minutes of research and I still have no fucking clue what any of it is, I'll leave that part of my education to university.

 

[ReadyAmyFire]

opted to do engineering in the end.

Which branch? I'm doing Aerospace. Niche but I find it fascinating.

 

[SckizoBoy]

No reason why. Either way next question is in. I'll ask a physics/chem question (not really chem).

OK, bring it!

Optically active substances take polarized light and change it's plane of polarization. Why is the effect cumulative when shining polarized light through a volume of the substance (i.e. why are the changes in polarization different when you shine the light through different concentrations or volumes of the material). Does each molecule of the substance rotate it by the same amount and so the more you have the greater the overall rotation?

WTF?! That's nothing to do with chemistry at all... *grr*

Anyway, I might be wrong in this, but I'll have a go anyway... my exposure to polarisation and its effects are largely limited to circular dichroism and the spectroscopic methods related there-to. Still, I think the effect rather unrelated to the quantity of substance it needs to pass through, since polarisation is necessarily the influence of the substance on the electric field and it also depends on which type of polarisation occurs. Granted its uses in spectroscopy, once the effect is made on the electric field, it cannot be further affected through encounter with further identical molecules in the system. For one reason or another, my mind cannot be torn away from crystallography...

Unless one of us is confusing this with refraction... >_>

Off topic: I am going into chemistry in university but I am also interested in physics. I just find it easier to ask questions in physics or I end up in questions like the one you asked, ten minutes of research and I still have no fucking clue what any of it is, I'll leave that part of my education to university.

Well, to be fair, the Ireland-Claisen rearragement is tremendously difficult to optimise and typically brings poor yields. Anyway, in many ways, chemistry is much more... intricate, shall we say, and synthetic chemistry in particular has several layers of reactive properties, a lot of which renders some properties very counter intuitive at second glance.

 

[Fractral]

Okay, I have one.
Is there an absolute point of refrence in the universe? If so, how do we find it, and if not, how can you prove it?

 

[xXGeckoXx]

No reason why. Either way next question is in. I'll ask a physics/chem question (not really chem).

OK, bring it!

Optically active substances take polarized light and change it's plane of polarization. Why is the effect cumulative when shining polarized light through a volume of the substance (i.e. why are the changes in polarization different when you shine the light through different concentrations or volumes of the material). Does each molecule of the substance rotate it by the same amount and so the more you have the greater the overall rotation?

WTF?! That's nothing to do with chemistry at all... *grr*

Anyway, I might be wrong in this, but I'll have a go anyway... my exposure to polarisation and its effects are largely limited to circular dichroism and the spectroscopic methods related there-to. Still, I think the effect rather unrelated to the quantity of substance it needs to pass through, since polarisation is necessarily the influence of the substance on the electric field and it also depends on which type of polarisation occurs. Granted its uses in spectroscopy, once the effect is made on the electric field, it cannot be further affected through encounter with further identical molecules in the system. For one reason or another, my mind cannot be torn away from crystallography...

Unless one of us is confusing this with refraction... >_>

Off topic: I am going into chemistry in university but I am also interested in physics. I just find it easier to ask questions in physics or I end up in questions like the one you asked, ten minutes of research and I still have no fucking clue what any of it is, I'll leave that part of my education to university.

Well, to be fair, the Ireland-Claisen rearragement is tremendously difficult to optimise and typically brings poor yields. Anyway, in many ways, chemistry is much more... intricate, shall we say, and synthetic chemistry in particular has several layers of reactive properties, a lot of which renders some properties very counter intuitive at second glance.

Hmm yeah, I have asked reddit /r/askscience there and yes it is not really chemistry related.

But the idea of it not being affected by the same identical system twice seems to be a little bit in the opposite direction of what I was taught, polarization is non-commutative right?

This is delving further into physics.

Off topic: I am going into chemistry in university but I am also interested in physics. I just find it easier to ask questions in physics or I end up in questions like the one you asked, ten minutes of research and I still have no fucking clue what any of it is, I'll leave that part of my education to university.

Are you at uni now or are you soon to be going?

Soon to be going.

 

[ReadyAmyFire]

Queens, they have the kit in order to do work on nano-technologies which sounds awesome.

Saying that, I may end up finding some other aspect more interesting and focus on that instead.

That does sound rather interesting, that's not Queen's Belfast you're refering to is it?

 

[xXGeckoXx]

Okay, I have one.
Is there an absolute point of refrence in the universe? If so, how do we find it, and if not, how can you prove it?

Ok since nobody is answering I'll give it a shot, my answer is not going to be particularly good since I know little about topology and the shape of the universe. In broad terms, no there is no real point of reference, one important thing to know is that there is no center (see my post above for more info about that), the shape of the universe is also quite strange (and mostly unknown) we do know for example that space is non-euclidean (read up on this, the gist is that it's pretty weird, for example the shortest path between two points does not have to be a straight line). This already messes things up quite a bit because normal definitions for points of reference don't work so well.

 

[ReadyAmyFire]

Sure is, I will hopefully be going there this year.

Either that or Uni of Ulster if I mess up in my grades. It's a hell of a drop. Queens is #9 in the UK for my degree while Ulster is in the 50's. I would still get the same degree at Ulster but I'd much rather go to Queens.

Well very good luck. Can't comment on UU but I love Queen's.

 

[Chromatic Aberration]

Optically active substances take polarized light and change it's plane of polarization. Why is the effect cumulative when shining polarized light through a volume of the substance (i.e. why are the changes in polarization different when you shine the light through different concentrations or volumes of the material). Does each molecule of the substance rotate it by the same amount and so the more you have the greater the overall rotation?

After checking in Gerthsen Physik [http://www.amazon.com/Gerthsen-Physik-Springer-Lehrbuch-German-Edition/dp/3642128939/ref=sr_1_1?ie=UTF8&qid=1340229937&sr=8-1&keywords=Gerthsen+physics] (the big all-encompassing german book of physics) it seems as certain quartz crystals as well as optically active molecules have a different refractive index[footnote]See also the corresponding Wikipedia article section theory - see that Delta n? That's it. [http://en.wikipedia.org/wiki/Optical_activity][/footnote] (i.e. the electromagnetic waves have a different speed[footnote] See for instance the Wikipedia article [http://en.wikipedia.org/wiki/Refractive_index] section phase speed and dielectric constant to see that[/footnote]) depending on if your light is positively or negatively circular polarized. This leads to a phase shift between the two. Since linearly polarized light is just a superposition of both, the phase results in a shift of the linear polarization depending on the size of the phase difference. It is clear that the more material you have or the greater the difference of the refractive index in your material, the more your polarization will be shifted. The change in polarization angle is proportional to either the width of the quartz or concentration times width (entering via the refractive index - how I can't say unfortunately).

As for the aspect if it is non-commutative, I'd agree. I had this as an example for the quantum mechanical measurement process in my QM lecture some years ago: since the polarized light is a superposition, a filter leads to a projection onto the direction specified by the filter. Your intensity gets smaller. Do that again with a different filter and the intensity gets smaller still. If both filters are not the same your intensity will vary depending what filter you use first. Hence, I'd say its non-commutative.

Captcha: bad books - Captcha, do you want to tell me something?

 

[xXGeckoXx]

snip

After checking in Gerthsen Physik [http://www.amazon.com/Gerthsen-Physik-Springer-Lehrbuch-German-Edition/dp/3642128939/ref=sr_1_1?ie=UTF8&qid=1340229937&sr=8-1&keywords=Gerthsen+physics] (the big all-encompassing german book of physics) it seems as certain quartz crystals as well as optically active molecules have a different refractive index[footnote]See also the corresponding Wikipedia article section theory - see that Delta n? That's it. [http://en.wikipedia.org/wiki/Optical_activity][/footnote] (i.e. the electromagnetic waves have a different speed[footnote] See for instance the Wikipedia article [http://en.wikipedia.org/wiki/Refractive_index] section phase speed and dielectric constant to see that[/footnote]) depending on if your light is positively or negatively circular polarized. This leads to a phase shift between the two. Since linearly polarized light is just a superposition of both, the phase results in a shift of the linear polarization depending on the size of the phase difference. It is clear that the more material you have or the greater the difference of the refractive index in your material, the more your polarization will be shifted. The change in polarization angle is proportional to either the width of the quartz or concentration times width (entering via the refractive index - how I can't say unfortunately).

As for the aspect if it is non-commutative, I'd agree. I had this as an example for the quantum mechanical measurement process in my QM lecture some years ago: since the polarized light is a superposition, a filter leads to a projection onto the direction specified by the filter. Your intensity gets smaller. Do that again with a different filter and the intensity gets smaller still. If both filters are not the same your intensity will vary depending what filter you use first. Hence, I'd say its non-commutative.

Captcha: bad books - Captcha, do you want to tell me something?

Non-commutativity is explained by representing polarization states as matrices. That explanation for crystals is fantastic thank you. I have been wondering about things like, what's going on inside a glucose solution which is optically active.

Since nobody seems to be picking up this thread I will keep going until I fall asleep.

I read a A level question which went as so "Why are diamonds cut at Brewster's angle?". What does Brewster's angle mean in reference to diamond cutting? And Why is it cut at Brewster's angle?.