Wonders of the universe (BBC) questions...

[Chris [BEANS]]

I'll put this here rather than the TV section because it's not really about the programme, it's just a couple of questions I have since watching it.
Hopefully there'll be a physicist or two around to help out?!

I have no knowledge of physics at all, but I do take a keen interest in it all. Love a book on quantum theory or a documentary on space. Don't understand the majority of what I read but that doesn't seem to make it any less fascinating!!


So.... Two questions I have from the episode:-

1. At the beginning was a very ancient 'calendar'. It was basically 15 piles of stones, with small gaps between them. If you stood at a certain point and looked at them at sunrise on the summer equinox, you'd see sun rise at the leftmost point.
If you were to do this daily, as the year progressed you'd see the sun rise further and further to the right.

My question is, what happens at the end of the year?! Obviously it doesn't just get to the furthest right point and then the following morning rise on the far left again, so I'm assuming it would start to make its way back across to the left, wouldn't it??
In which case, unless you knew which year you were in the position of the sun at sunrise could mean one of two different dates.
Or am I way off?!


2. Apparently the 2nd law of thermodynamics is that entropy always increases.
Not a word I'd ever heard before, but following the explanation given this makes sense and I'm happy with the concept.
However...
As I understand (admittedly I have a very limited understanding), following the big bang the universe was just hydrogen and a bit of helium knocking about, but this ultimately coalesced to become stars, which in turn created heavier elements that later formed planets etc....

Surely this creation of stars and planets is an example of a disordered universe (random atoms/elements knocking around in the vacuum of space) creating ordered objects of its own accord (the coalescing of these elements due to gravity). Precisely the opposite of what the law states?!

I know I'm wrong, because the law says I am, but I can't see how or why!!

Anyone kind enough to answer, please try to phrase things so that a stupid bloke can understand them.

Ta

 

[Strife212]

Not sure about the first q but

2. Apparently the 2nd law of thermal dynamics is that entropy always increases.
Not a word I'd ever heard before,

Thermodynamics

 

[Chris [BEANS]]

Not sure about the first q but



Thermodynamics

I know, that's what I wrote!!


lol

 

[daz]

[QUOTE='Chris [BEANS]
Surely this creation of stars and planets is an example of a disordered universe (random atoms/elements knocking around in the vacuum of space) creating ordered objects of its own accord (the coalescing of these elements due to gravity). Precisely the opposite of what the law states?![/QUOTE]

For entropy to decrease in one area of the universe, it has to increase somewhere else.

 

[Deadbeat]

1) The date would be assessed in relation to previous days to get one of the two possible dates, but yes, any single recording can represent two dates in the year

2) I may have to look in to this more, but this sounds like the Gibbs Paradox - reading up on that might answer your own question, which I find is always the best way to learn.

Edit: And yes, in 1) the sun will march back along the line, which is why each position can represent two dates, apart from the first and last. Although if you're being pedantic about it, each position can only correlate to one date because of the inconsistencies in the annual calendar - that extra 1/4 of a day that gives us leap years. As such, each position can only refer to a single date once every 4 years - so if it were recorded accurately enough, you could not only calculate exactly what date it is but also when the next leap year is due.

 

[The $6m Dan]

1) The sun goes back and forth along the stones.
At the summer equinox the sun is at the left most stone (Summer) and then goes through autumn to the right most stone, at the winter equinox. Then it works its way back across the stones during spring as the days get longer.
(edit - Didn't fully read the question. So yes you're right)


2) You're right to say that the creation of stars and planets is an example of ordering but it is localised and is only temporary. Ultimately they will be destroyed.
Edit for additional info. As it said on the program there is nothing to stop the universe from randomly making a sandcastle, it's just incredibly unlikely. However, the creation of planets and stars is aided by gravity so the probability is far less.

 

[BetaNumeric]

In regards to the thermodynamics of stellar formation you have to include things like available useful energy. By collapsing under gravity energy is 'released' in the form of kinetic energy, which then gets turned into heat due to collapsing material bumping into itself. As a result you find you have turned a large amount of material with lots of useful energy content into a slightly different ordered form but some of the energy has been 'dumped' into thermal energy.

A simpler example is fusion in a star. One of the fusion cycles effectively turned 4 protons into a helium nucleus and a bunch of energy. You might consider the 4 protons are 'disordered' and He as 'ordered' and consider it to be a contradiction to the 2nd Law but you have to include the energy which has been produced. Several MeV of energy are released and ultimately turn into heat, either thermal or photon based. When you include this in your calculations then you find entropy has increased.

For entropy to decrease in one area of the universe, it has to increase somewhere else.

This is not necessarily true. The 2nd Law is more a rule of thumb than a law if you consider short term effects. The typical example is the gas molecules in a room. They bounce around all the time but nothing seems to happen much from our point of view. From this we can define things like temperature and pressure for a gas, as large scale (macrostates) effects. If you could magically determine the position and motion of every single particle then you would be measuring the 'microstate' the gas it in. Many microstates lead to the same macrostates and the most numerous equivalent microstates are, almost by definition, those corresponding to the largest entropy. However, there's plenty of other microstates, with lower entropy, which the gas could move into simply by further bouncing around. The vast majority lead to macrostates so close to the usual ones that we don't notice but there's some with wildly different pressures and temperatures. In fact, its not impossible for all the gas particles in the room you're in at the moment to end up in the corner of the room, as if compressed. How likely is it? You'll have to wait longer than the age of the universe to see it occur naturally. This is why it is such a good rule of thumb, the larger a 'violation', the rarer the event is.

For those interested in the specifics of such 'quirks' of thermodynamics (and certain dynamical systems in general) Wiki the Poincare Recurrence Theorem.

Oh and long time no see Daz

 

[Chris [BEANS]]

Cheers all I get it now (pretty much!!) and have some more geeky things I won't fully understand to google or Wiki to keep me entertained too!! Stand by for more questions on what I've read!!

And BetaNumeric.... Gotta love someone with 3 posts who comes out with a reply like that!!! Welcome

 

[Destination]

Q1,
It goes up then down, up then down, so top rpresents longest day, bottom shortest day, and every space inbetween represents 2 days, depending on direction of travel.

Q2,
Each atom has a mass/energy ratio, some are most stable than others, radioactive atoms fall apart (fission) on their own and tend towards atoms which contain less energy. Atoms such as hydrogen, when burned in a fusion style process, create helium, which overall contains less energy.

I think iron is one of the most 'stable', least energy containing atoms,a nd most things at a fusion/fission level tend towards it. Eventually iron in the cores of black dwarfs will cool and lose its own internal heat, thus giving off last energy, and a very very slow rate (trillions upon trillions of years) will eventaully completely degrade into energy, thus entropy increases.

Hydrogen the basic starfuel is energy high internally and will tend to low, thus disordered.

 

[Noxia]

I loved that program. Really like the presenter too, he seems really passionate about the topic.

 

[SiriusB]

The ancient stone calendar is no different to a 12-hour clock.

If your 12-hour clock says it is 10:30, you know from context whether it is in the morning or evening.

With the stones, you will know which time of year the date relates to based on its context. If you are freezing your knackers off, it's a safe bet it is the Winter date rather than Summer, for example.

 

[Chris [BEANS]]

The ancient stone calendar is no different to a 12-hour clock.

If your 12-hour clock says it is 10:30, you know from context whether it is in the morning or evening.

With the stones, you will know which time of year the date relates to based on its context. If you are freezing your knackers off, it's a safe bet it is the Winter date rather than Summer, for example.

Sort of....

But if you're freezing your knackers off it could be a week prior to the winter equinox or a week after.
Admittedly, if you witness the sunrise two days in a row you would know whether the sun is heading left or right on the scale.
Obviously, in a society that measures time with rocks, being a day or two out won't make much difference but you see my point.......


I know I'm being pedantic, but I'm not doing it to be a tw@, just because I'm interested and didn't fully understand so I'm just getting it straight in my head

 

[QuagmireUK]

Someone needs to rewatch this and count the number of times this bloke says "Billion". Its a joke.

 

[goujon945]

Someone needs to rewatch this and count the number of times this bloke says "Billion". Its a joke.

Ha! Carl Sagan was well known to have the exact same habit, didn't stop him from being an incredible popular science author/presenter/academic etc. Also the famous 'pale blue dot' passage in his book is beautiful.

Brian Cox on the other hand was in a **** band!

 

[Fusion]

Microstates and macrostates. One of my thermodynamics lecturers was from Bulgaria and he couldn't enunciate those words in a way that made them distinguishable, you never knew which one he was talking about. Anyway, sorry!

Oh and Hi Beta

 

[SiriusB]

Sort of....

But if you're freezing your knackers off it could be a week prior to the winter equinox or a week after.

The stones are calibrated to the two equinoxes, so I would assume in such a society they would make a point of observing those two dates in any given year. The same way we as a society always know when it is Christmas Day or a bank holiday. So, with that in mind, there is a good chance you already know which side of an equinox you are on.

Granted if you live under a rock and didn't know you just had or there was about to be an equinox you're stuffed. Though similarly if you passed out and woke up in a room with no windows, you can't be sure which side of noon that 10:30 is!

So in short, again, it is about context. It is not ideal, but what more do you want from a pile of rocks 2500 years old lol.

 

[Chris [BEANS]]

So in short, again, it is about context. It is not ideal, but what more do you want from a pile of rocks 2500 years old lol.

lol, fair point

 

[BAppleton]

brian cox acts and looks like james blunt. he even has a fascination with the stars. Its a good series but a bit boring, but then physics is

 

[Burnsy2023]

On a bit of a tangent, i saw Brian Cox at the Douglas Adams memorial lecture last week. He made a comment that stuck with me: unless there is other intelligent life, the LHC is the coldest place in the universe.

 

[BetaNumeric]

Its a good series but a bit boring, but then physics is

I don't mean this in an overly harsh way but that's an extremely naive comment to make. Is technology boring? It's all based on physics. Is space travel boring? Or the internet boring? And I don't mean specific websites but the concepts its based on, like instantaneous global communication from something the size of your wallet in the middle of an empty field. GPS locating uses billionth of a second timings and corrects for the fact the Earth warps space as it turns, all so you can find the right turning on the M6. What about the LHC? As just said, if there's no other life out in space its the coldest place in the universe. It can probe conditions which haven't existed since a billionth of a second after the big bang. Hubble and WMAP look back in time into space to when the first galaxies were being formed (and earlier!). LIGO searches for colliding neutron stars using 4km long lasers in vacuums more perfect than space, trying to find a variation in the laser length less than a proton's width as a gravitational wave passes through it. Its so sensitive it can detect when its raining by the change in gravity. Or the ICEcube neutrino telescope at the South Pole. A cubic kilometre of ice used to detect neutrinos from the Sun and supernova, which allow us to look into the core of stars.

What you mean is you found the algebra and mathematics of physics boring. Personally I find it very interesting. The fact you can start with a few basic concepts like "Inertial motion doesn't alter physics" and "Inertial observers agree on the speed of light" and within a few whiteboards of work conclude that time dilation should exist and that energy and mass are related is amazing.

Even if you don't understand and don't want to understand the details to say that 'physics is boring' is daft. You're on a computer, the result of physics research, connected to other computers in such a way as to have pretty much all human knowledge at your finger tips and you're living in a culture built upon scientific discoveries.