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Stupid Science Questions 2

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12:17 / 01.03.06

Reidcourchie - They'd both look like big flat thin surfaces, unless they operated on radiation in the optical frequencies. If that were the case, from what I can tell, the Diode Sail would be see-through from one side (and that side would face the direction of travel) and opaque on the other (so it would pass photons from one side through itself, and they would make no difference to its movement, but stop them on the other side, and the radiation pressure (the effect of being hit by billions of photons) would give a net forward motion). The induction sail, if it operated in the optical spectrum, would probably be opaque both sides and have some kind of bright light source behind it. To post links, btw, just use normal HTML.

Future Perfect - The five fruit and veg was made up by the fruit and veg marketing board, there's nothing special about the number. I recall a paper that suggested that nine smaller portions of different fruit/veg was a better target. So basically, to eat right, eat as wide as possible range of things with fresh fruit and veg making up the majority of those, and don't eat empty (i.e. non-nutritious) calories. Potatoes and juice don't count as fruit/veg, either. Healthy diets have got to be fun, though, or it's impossible to stick to them long-term. If you do feel the need to eat rubbish, make sure it's nutritius rubbish. A real beef-burger on a brown-bread bun with real salad is much better for you than a Big Mac. You can count that salad as a portion of fruit/veg, too.

pointless & uncalled for

13:00 / 01.03.06

The number five in the portions of fruit and veg wasn't entirely pulled out of thin air. There is at least a little theory behind it. The idea is to introduce variety into the diet to ensure a proper uptake of nutrients on a daily basis and capitalise on the benefits that nutritional isovarience has on the human biology. Yes it came from a marketing board who stand to benefit from the public buy in, but it doesn't make the practice bad as the notion is fundamentally sound albeit not perfect or absolute.

Alas the explanation behind the thinking isn't quite snappy enough to put on packaging and certain points have been lost in translation.

One key thing that any healthy dieter should consider is that over the years food culture has veered towards larger portions of meat and filler and lost vegetable content. If you find cutting down leaves the stomach wanting then rather than eating less, alter the proportions on the plate and thus ween your palate and digestive system off of that is less conducive to good health.

15:03 / 01.03.06

What I was trying to say was that the number five is not significant, it was thought best for marketing reasons. There's nothing magic about it at all, easting more than five fruit/veg is appreciably better than stopping at five. Eating more fruit and veg, probably less meat (certainly less beef, chicken and pork), and definately less refined carbohydrate is the way to go. Obviously freshly prepared food is better than frozen/instant/readymeals (with the possible exception of peas and sweetcorn) too. If you want a veg you might not have had before (it's a tricky time of year for local produce) then try purple sprouting brocolli.

20:29 / 17.03.06

Okay, I have a question that’s been bugging me for quite some time. We’ve all read articles or papers about astronomers taking snap shots of the early universe or something like that. How is this possible? Is there a place we can point the Hubble toward and say, “Oh look, it’s moments after the Big Bang! Isn’t the universe cute?” Can telescopes peer backward in time? If so, how?

13:40 / 18.03.06

Because light takes time to travel here. If something is 100 light years away, we're seeing it us it was 100 years ago. Even light from the sun takes about 8 minutes to reach earth.

tom-karika nukes it from orbit

15:21 / 18.03.06

Because of the way the universe formed, that 'distance' between us and the big bang wasn't actually there when the light set out.

So a few billion years ago, we and the rest of the universe were at a point. Suddenly the big bang happens, and the density of matter in the universe drops as the universe expands. It's extremely hot, so it's radiating light in all directions, from all places.

Now at some time after the big bang, the matter starts to condense and we get stars and galaxies forming - there are gaps in the matter, and these gaps get bigger as the universe expands and the matter condenses. The stars and galaxies move further and further away from each other, or rather the gaps in between them get bigger and bigger. Light travelling between these stars takes longer and longer to cross these gaps

So, a few billion years later the gaps are huge, but the radiation is still travelling. So if we look far enough away, we can see light that has been travelling since nearly the beginning of the universe.

This light is very faint and redshifted, so picking it out requires enormous telescopes - and we can't see any further back than when the gaps start to appear in the matter. But we can see things that happened a very long time ago.

15:22 / 18.03.06

So if we're looking at something that's 100 light years away, which means we're seeing it how it was 100 years ago (earth time), how can we be sure it's like that now? I guess we can't.

15:24 / 18.03.06

Thanks, Tom.

09:46 / 20.03.06

You're right, we can't know what's happening right now to anything, but in a way it doesn't matter, because none of their effects can reach us before the light anyway (so current theory goes).

The right-after-the-big-bang information is sligltly different, it's due to study of the cosmic background (the "static noise" that just exists everywhere in the universe, and can be explained with the really poor analogy that it's the echo of the big bang). There have been some recent breakthroughs in the sensetivity of measurement, which have validated some interesting models, afaik, that give us a better idea of the processes at work in the time shortly after time started.

10:08 / 20.03.06

Ok: more fruit and veg. Recently I had some fruit in the fridge and forgot about it, and when I checked it one of the pieces was off (only a little bit wrinkled - we’re not talking mould here people) but the others appeared to be fine though they were there the same length of time. So my stupid fruit and veg question is: why does one piece of fruit/veg go off before the other?

I’ve noticed this before, but I’ve never been able to work out why one piece of fruit would “sacrifice” itself for others of the same type, presumably of the same “age”. I’m pretty damn sure this isn’t the galvanisation process that I remember from school chemistry (!) – so what is it? Is it an actual “thing” or just an awry observation?

10:37 / 21.03.06

I think it's just a statistical effect... you'd probably find that one or two things go off first, then (assuming they don't affect the others, for example if they go mouldy)the majority will go, with a couple lasting a bit longer. A classic normal distribution.

Some fruit are probably riper than others to start with (more sun, different place on the plant, different plant), and some may have been more damaged by transit (they were on the edge of the box, or they got dropped) which could lead to them spoiling first. With your fruit going wrinkly, that suggests water-loss (fridges and freezers are very good at drying things out), so damage to the fruit skin, or a less developed, thinner skin to start with could be the cause. I don't think off the plant there's any notion of sacrifice for the larger organism. After all, fruit wants to be eaten, that's it's distribution model, and after it leaves the plant it's very much on it's own.

12:19 / 21.03.06

Aha! Thank you. A very sensible answer to my possibly-I-have-too-much-time-on-my-hands question.

22:52 / 29.03.06

What size are things? What are the smallest things, and what order do they go in? What are the largest things?

22:48 / 04.04.06

I walked through a patch of 'thick air' today. It was a bit like walking through wind or jelly, but it was only on my leg, there was nothing to see and it was in my house.

Is there such a thing as 'thick air' and if so what is it? If there isn't, is there any kind of weird body change that might cause this sensation, and why did it only happen on my left leg?

11:44 / 05.04.06

fred: What size are things? What are the smallest things, and what order do they go in? What are the largest things?

The Powers of 10 Java tutorial will answer that question.

Lula I walked through a patch of 'thick air' today. It was a bit like walking through wind or jelly, but it was only on my leg, there was nothing to see and it was in my house.

Is there such a thing as 'thick air' and if so what is it?

There are all kinds of thermal pockets in air, just like the thermal pockets (and thermoclines) in water. On a large scale, these things are what cause weather -- a low pressure zone tends to bring rain and makes animals get a little wiggy.

It seems weird to me that there'd be a tiny zone of measurably high or low pressure inside your house, though (on the large scale, these are generally surrounded by areas of wind & rain -- weather fronts). I'd bet it was a temperature difference (possibly from convection) you were registering.

00:49 / 10.04.06

I was talking with a friend a while ago about RAW's 'Quantum Psychology' and the interesting links it made between human action and perception, and quantum theory (or at least i was trying to - i may have been a little tipsy..)

And he said something along the lines of "nah, quantum physics is bollocks; it's all about string theory these days". He seemed to be of the impression that most of the theories formed from the observations of quantum physics had now been disproved.

This worried me a little, cos i've only just started to understand some basic QP, and was starting to quite like what it had to say, and it's such a chore to have to drop an old scientific world-frame and take up a new one...

So is string theory really 'where it's at' nowadays? Has QP been 'disproved'? If so, how? What's a good place to learn about these things?

tom-karika nukes it from orbit

10:16 / 10.04.06

No, quantum physics is certainly not 'disproven' - much like Newtonian mechanics isn't disproven by Special/General relativity. Quantum mechanics still works - in fact as a theory it's pretty good at prediciting a lot of stuff extremely accurately.

But, just as regular mechanics seems to break down with light speed, Quantum mechanics seems to get into a mess when you add in gravity. So we get String theory, which is going in the direction of putting gravity in to sync. with quantum mechanics.

So don't stop learning about quantum mechanics on the basis of string theory - string theory is quantum mechanics with modifications and additions for gravity.

It's part of the nature of physics that we keep adding layers of approximations - we need to use the correct approximation to predict the situation. So if I want to know what happens when a cat falls out a window, I use Newtonian mechanics. If I want to know what happens when a cat falls out of a window from a spaceship travelling near light speed, I use Relativistic mechanics. This doesn't mean that regular newtonian mechanics isn't worth knowing. If I want to know what happens when an electron falls out of an excited state in a Helium atom, I use regular quantum mechanics. If I want to know what happens to that same electron and I throw in some gravity, I use a string theory.

Remember that string theory is very, very new.

11:06 / 10.04.06

"nah, quantum physics is bollocks; it's all about string theory these days".

String theory has yet to predict anything that could be falsified. It's a large collection of fun ideas, mostly of a highly mathematical nature. QM is physics.

If you are interested in modern physics, I suggest you buy Roger Penrose's The Road to Reality: A Complete Guide to the Laws of the Universe.

tom-karika nukes it from orbit

11:56 / 10.04.06

I agree, that is a fantastic book. Go buy it, everyone.

14:04 / 10.04.06

Thanks. I'll get myself a copy once i have a little cashflow.

A couple of the reviews on amazon say that the book is very maths-heavy: often 'too' maths heavy.. The last time i did maths was at gcse..

So i suppose another stupid question - can you recommend any good books or internet resources that will help me get my maths knowledge up to par for reading this book?

15:58 / 10.04.06

Sorry, metro.tramp, I don't think I can suggest a single book. Remember, you so only want to understand the principles involved, you don't actually want to perform detailed calculations. I think its important to see mathematics as a language, rather than either a calculating system or THE TRUTH, when one is using it to frame and understand physics. It's the physical principles that matter, mathematics is merely an unusually precise language to describe those principles.

If Penrose's account isn't detailed enough I'm not sure how good the Wikipedia is on these subjects, but I certainly would look there first. After that I think you'd best visit a library and seek a book that suits you. Modern physics applies above all two branches of mathematics, group theory and differential geometry. Each of these is the subject of tens of thousands of books at every conceivable level of detail.

Or you could just ask me of course, and I'll do my best to explain whatever it is.

Of course if you're not in quite such a mad rush to get to String Theory you might do better starting with the Feynman Lectures On Physics.

03:24 / 11.04.06

second that, feynman's 'six easy pieces' is a great way to start to think about physics.

05:51 / 11.04.06

To answer fred's question regarding the smallest thing. It's the Planck length. Smaller than that its not clear that space and time is well-defined at all.

12:20 / 12.04.06

So um
Mass.

what is it? I know it's defined as something like gravity over weight or something...
Actually.. how is it defined?

And what is it? Is it just an abstract concept?

Why does it vary? Why does sponge have more mass than brick?
As my friend put it: "'cos it has less particles in it to interact with gravity. each of those particles then reacts to gravity and are made up of quarks which dont react with gravity, so where does the mass come into it?"

?

12:49 / 12.04.06

New question.

Why is it if you burn yourself it hurts all over again if you put the burn under hot water?

I spilled hot goose fat on my hand whilst making dinner last night and then went for a bath, and the burns hurt all over again when my hand was under the water.

tom-karika nukes it from orbit

13:36 / 12.04.06

There are three 'base' definitions of mass:

First, the inerta of an object - I apply a force, I get an acceleration dependent on the mass - higher mass, lower acceleration. Of course, this depends on the defnition of a force, which is defined by the mass... What we end up doing is picking something, saying 'This has mass of 1kg'. To measure any other masses, I compare the acceleration of those masses to that one reference mass under the same force.

Second, the gravitational field from an object defines it's mass. e.g. the higher the mass, the higher the gravitational field that mass exerts.

Thirdly, you can define mass by the effect of a known gravitational field - a known field has more effect on a larger mass.

Numbers Two and Three are really the same thing - but they're quite distinct from the First, conceptually. You have to show experimentally that gravitational and inertial mass are equivalent (which obviously they are).

All Acting Regiment

01:31 / 13.04.06

Jub- I'd think it's because you've killed the top layer of skin in the burning, so the underlayer is vulnerable and sensitive to, say, hot bathwater. Probably would hurt in the wind as well.

09:13 / 13.04.06

Why is it if you burn yourself it hurts all over again if you put the burn under hot water?

I spilled hot goose fat on my hand whilst making dinner last night and then went for a bath, and the burns hurt all over again when my hand was under the water.

Due to the nature of the body's response to injuries the sensitivity to pain of the area around the burn will be increased. The nerves that detect hot/cold will have been over-sensitised by the initial burn event as well. So they read heat as being "hotter" than it actually is.

15:38 / 25.04.06

on burns - I was in an auto accident some time ago, and the airbag burnt my forearm pretty badly. I noticed increased sensitivity, also - strong wind really hurt, but blowing softly on it actually felt pretty good.

06:00 / 27.04.06

...and we're all steadfastly letting that last remark pass thru to the 'keeper

anyone know what's going on when people tell you they're 'double jointed'?

presumably, this is not literal - how does the hyperflexibility work for these people - what's the pay-offs [easier to pull out joints, etc?] and is this something that contortion training, yoga, etc can attain, or is it just how you're born..?

Henningjohnathan

15:40 / 08.05.06

Could someone explain the "delayed double slit" experiment as Jenny Randles describes in her book BREAKING THE TIME BARRIER.

Essentially, as I understand it from the book, in the classic double slit experiment, a single source of light is shown through a sheet with two side by side slits cut into it. There is a sheet behind so that the observer can see the pattern the light makes. When the light is allowed to flow naturally, it makes an interference pattern on the sheet with one bright area in the center equidistant from the two slits (this is "wave" behavior). When a "photon detector" is placed at the slits, then there are two bright spots right behind the slits (this is "particle" behavior).

Thus, light behaves as a wave or a particle depending on which behavior you look for.

However, she then described a "delayed" double slit experiment where the "photon detectors" were or were not turned on after the light passed through the slit. In the cases where the detectors were turned on after, the light behaved like a particle, and in the cases where they were not turned on at all, the light behaved like a wave. The implication, of course, apparently is that the light "knew" what the photon detectors were going to do "in the future" and therefore effect precedes cause.

This is like saying you will unlock the door in the past because you opened it in the future.

Is this the implication of the experiment? Exactly what are photon detectors? Also, aren't our eyes essentially double slits (two pupils)? Would the retina act as a photon detector? Would our "minds" act as the sheet behind the slits?

16:17 / 08.05.06

The delayed double-slit experiment is definitely one of the hardest concepts to grasp in physics, partly because there isn't anything we can really relate it to by analogy on the macroscopic scale.

As I understand it, there are a couple of different theories that deal with this phenomena. Feynman suggested that the photon actually takes every possible path between the source and the target, and that by introducing a detector, it alters the possible paths that the photon can take by becoming a new "target." Then again, Feynman himself says that this is a remarkably bad analogy for what he's trying to explain, so I'm not sure how helpful it is.

The alternate theory is that there is a "probability wave" that defines the probability that the photon will be at any given point. Due to Heisenberg's uncertainty principle, it's impossible to know the *actual* position of the photon without affecting it. The particle detector in the path of the photon must interfere with it in order to detect it, and so it makes sense to me that this interference alters the outcome of the experiment. Whereas in absence of the detector, the wave was free to interfere with itself.

As far as our pupils go, to my understanding the spacing of the slits must be close to the wavelength of light for the double-slit experiment to work. Our eyes are far apart enough that there certainly is no double-slit effect at visible wavelengths.

An interesting thing to think about is how the double-slit experiment looks from the perspective of the photon. According to my understanding of general relativity, time experienced by an object in motion flows at a rate inversely proportional to the velocity of that object as it is regarded by an outside observer, with the passage of time from the perspective of the object going to zero as the object nears the speed of light from the perspective of an outside observer. This is to say that from the perspective of a photon, no time passes between its initiation at the light source and its arrival at the target. For the photon, space is curved in such a way that the source and the target are the same.

Grasping exactly what this means from our perspective is the purview of more learned people than I.

Henningjohnathan

17:37 / 08.05.06

Yeah, it would seem that since at the speed of light NO time passes, then from any photon's perspective it is everywhere simultaneously. Except what about photons that fall into Black Holes? It's totally crazy.

20:20 / 18.05.06

Sorry to jump backwards, but re the one piece of fruit going off first...

I suspect that it's common practice in supermarkets to shift old fruit by packing it into plastic punnets or net bags, with a few fresher pieces. While it's in plastic, and surrounded by slightly fresher fruit, you're less likely to notice that one shrivelled plum...

21:17 / 18.05.06

Regarding photons.
From the protons point of view it takes "no time" to travel from the point of emission to the point of absorption. This is because it is traveling along a "null line". All massless force carrying particles travel along these lines through spacetime. However as conciousness seems to require some vessel that has mass this point of view is unobtainable.
As for what happens when a photon hits a spacetime singularity - nobody knows - if they did, they wouldn't be able to tell anyone anyway for they would have hit the singularity as well.

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