Things about science and nature you find interesting

[Instant K4rma]

Ive always been interested by astronomy. I hope that scientists can figure out what "Dark Matter" really is soon, because i really want to know!!

 

[oktalist]

[del]Black[/del] dark matter...

Can't be seen, can't be felt or tampered with, can't be contained by anything man made..

Who says it can't be felt, tampered with or contained?

I was going to say, it's just a catch-all term for matter we can't see, isn't it?

Not really. It's theoretical matter that is postulated to exist to account for the fact that the rate of change of expansion of the universe is different from what we would expect from gravity acting on the mass of matter that we know about. We know we can't see it because we point our telescopes all over the sky and receive no electromagnetic radiation (light, radio, x-ray, etc.) consistent with its presence.

X = total mass of all matter that we know about;
Y = what the total mass of all matter would have to be for the universe to be expanding in the way it appears to be;
dark matter = Y - X.

Either there's dark matter (i.e. matter we don't know about), or we're measuring the expansion of the universe wrongly, or there's something wrong with our theory of gravity. Or there's something else crazy going on.

 

[pffh]

lots of stuff

The twin paradox explains this pretty well.

http://en.wikipedia.org/wiki/Twin_paradox (I know it's only wikipedia but it's good enough)

 

[Ajna]

Similar to the Theory of Relativity one, but a bit more specific:

Because the faster you go, the slower time goes for you, theoretically, there is a speed you can reach where time would actually appear to flow backwards to you. E.G.: Time Travel. Because of that whole "Fly 500 lightyears away, then come back" bit, which means you could go 1000 years in the future and age a day, this means you'd be able to come right back, too. Naturally, we can't actually reach these speeds, but the concept is cool.

Mainly because I'd go 1000 years into the future, swipe something cool, and come back and claim to have invented it. If your head just exploded, that's okay.

That's erm not how it works.

Me and a physics major already went through that particular arguement on pages 1 & 2 of this thread...

Ah sorry didn't see that. Seems he has explained everything I'll just go and be useless in the corner.

It's okay. I put two beakers of water in the corner, and an apparatus to generate an electric current between them. So you can make a 15cm water bridge!

Oh, and there's chocolate milk there, too, so there's always that...

 

[Ajna]

lots of stuff

The twin paradox explains this pretty well.

http://en.wikipedia.org/wiki/Twin_paradox (I know it's only wikipedia but it's good enough)

This seems to be confirming what I said: That the earth did age 500 years, not one day...

 

[Danny Ocean]

*snip*

So it's to explain away situations where we're getting gravity from supposedly nothing?

 

[pffh]

lots of stuff

The twin paradox explains this pretty well.

http://en.wikipedia.org/wiki/Twin_paradox (I know it's only wikipedia but it's good enough)

This seems to be confirming what I said: That the earth did age 500 years, not one day...

Here is the example they use on wiki

Consider a space ship traveling from Earth to the nearest star system outside of our solar system: a distance d = 4.45 light years away, at a speed v = 0.866c (i.e., 86.6 percent of the speed of light). The Earth-based mission control reasons about the journey this way (for convenience in this thought experiment the ship is assumed to immediately attain its full speed upon departure): the round trip will take t = 2d / v = 10.28 years in Earth time (i.e. everybody on earth will be 10.28 years older when the ship returns). The amount of time as measured on the ship's clocks and the aging of the travelers during their trip will be reduced by the factor \epsilon = \sqrt{1 - v^2/c^2}, the reciprocal of the Lorentz factor. In this case \epsilon = 0.500 \, and the travelers will have aged only 0.500×10.28 = 5.14 years when they return.

The ship's crew members also calculate the particulars of their trip from their perspective. They know that the distant star system and the Earth are moving relative to the ship at speed v during the trip. In their rest frame the distance between the Earth and the star system is εd = 0.5d = 2.23 light years (length contraction), for both the outward and return journeys. Each half of the journey takes 2.23 / v = 2.57 years, and the round trip takes 2×2.57 = 5.14 years. Their calculations show that they will arrive home having aged 5.14 years. The travelers' final calculation is in complete agreement with the calculations of those on Earth, though they experience the trip quite differently.

If a pair of twins are born on the day the ship leaves, and one goes on the journey while the other stays on Earth, they will meet again when the traveler is 5.14 years old and the stay-at-home twin is 10.28 years old. The calculation illustrates the usage of the phenomenon of length contraction and the experimentally verified phenomenon of time dilation to describe and calculate consequences and predictions of Einstein's special theory of relativity.

See because from the travelers perspective the distance traveled is much shorter then from the perspective of the people on earth thus all calculations match and there is no paradox.

 

[Sovreign]

The fact that I can take compressed air, electrify it, turn it into the FOURTH STATE OF MATTER and cut through 2 inches of steel like butter. That's amazing.

 

[oktalist]

Also, I have a problem with this effect that no-one seems to have twigged: surely the equivalence of inertial reference frames means that a spaceship travelling away from Earth at .9c is equivalent to the Earth travelling away from the spaceship at .9c, so it is equally correct to say that both (a) the spaceship aged 1 day while the Earth aged 500 years and (b) the Earth aged 1 day while the spaceship aged 500 years.

I'm sorry, but statement (b) just is not making sense to me there...

Physics doesn't have to make sense.

It's the logical conclusion that comes from realising that "spaceship travelling 'north' while everything else stationary" is the same as "spaceship stationary while everything else travelling 'south'".

I'm pretty sure physics does have to make sense. I think congress passed a law regarding it in '86.

But yeah, it still doesn't make sense. If the earth had only aged one day, then how is it that 500 years worth of time still passed for the people on it?

It didn't. You misunderstand me. When I said the Earth aged one day, I meant that the Earth and everything and everyone on it, and in orbit around it, and everything else in the solar system, all aged one day.

If one object is moving with respect to another, the latter is moving with respect to the former and with equal relative speed.

The astronaut thinks he has aged only one day while 500 years have passed on Earth. But the people on Earth think that they have only aged one day and the astronaut has aged 500 years and is now long dead. From the perspective of the astronaut, he returns to Earth 500 years in his future, having aged only one day. From the perspective of the people on Earth, a spaceship crashed to the planet's surface one day after it took off, with a 500 year old skeleton on board.

I think that's the interpretation, anyway. All our basic assumptions about simultaneity break down when we realise that the speed of light in a vacuum is a constant across all frames of reference. Just because observer A sees two events as happening simultaneously, doesn't mean that observer B will see them happen at the same time, if A and B are in near-lightspeed motion relative to each other. There is no absolute measure of time by which events could objectively be said to be simultaneous, and no frame of reference is more valid than any other.

Is there any "For further reading" postscript you can add for me?

Yes, thankfully Wikipedia has it: here [http://en.wikipedia.org/wiki/Time_dilation#Time_dilation_is_symmetric_between_two_inertial_observers]. "Time dilation is symmetric between two inertial observers."

 

[z121231211]

A cat can get through any small space as long as it's head can get through.

I think that was the rat.

 

[throwitinthetrash]

If I enjoyed being in debt for three-quarters of my life, I'd've majored in physics.
Magnetism is hawt. Quick, wiki link me something interesting.

 

[oktalist]

*snip*

So it's to explain away situations where we're getting gravity from supposedly nothing?

Well it's the most likely explanation of the one situation where the universe is apparently getting gravity from somewhere unseen. But "explain away" makes it sound like cheating, like an ad hoc hypothesis invented to save a broken theory, as in "dinosaur fossils were put there by God to test our faith." But like when the theory of gravity was contradicted by the orbit of Uranus and a theoretical extra planet was postulated whose gravity would account for the discrepancy, which later turned out to be Neptune, hopefully one day the presence of dark matter can be either confirmed or disproved. If it's confirmed, cool, let's find out what it is then. If it's disproved, cool, let's find out what's wrong with our theory of gravity then, or what other effect is causing the apparent rate of expansion of the universe to be different from what we expect.

 

[Bulletinmybrain]

Life.

We evolved from tiny unicellular archaebacteria^1, into multicellular organisms.. But why? We are less suited to our environments now? What triggered the evolution to regular bacteria you and I know? Why did it then evolve into things such as protists, fungi, plants, and animals?

1: Archaebacteria thrive in the absence of oxygen.. What created the oxygen?

 

[oktalist]

We evolved from tiny unicellular archaebacteria^1, into multicellular organisms.. But why? We are less suited to our environments now? What triggered the evolution to regular bacteria you and I know? Why did it then evolve into things such as protists, fungi, plants, and animals?

Plants and animals didn't replace bacteria; we filled a different niche; bacteria still exist in their own niche and we in ours. We're no better or worse than bacteria, just different. We developed from them, but we're adapted to different environments. What enabled the evolution of complex organisms was groups of bacteria entering into mutually beneficial alliances that resulted in better reproduction for all concerned.

And you use the word "triggered" as if evolving from one form to another is a discrete event, when it actually happens gradually, bit by bit. We can classify individuals after the fact into different species and phyla and so on, but evolution in action is a continuous process of very small changes in each generation. It has a lot to do with the evolutionary arms race. Evolution is a process of adapting to an environment, but the environment is not static; it includes other entities which are also evolving. As one group evolve bigger teeth so another group evolve thicker skin. As one group evolve camouflage so another group evolve better eyesight. Eventually it will reach a steady state but the environment is always changing and stirring the cauldron again.

1: Archaebacteria thrive in the absence of oxygen.. What created the oxygen?

Cyanobacteria.

 

[PersianLlama]

Science is just awesome. I find all of it fascinating. However, I find Evolutionary Biology and Biochemistry the most interesting.

 

[cuddly_tomato]

Yes but as I said to the other fellow, that success doesn't actually mean much when we are trying to explain how it got there. Look at the examples of bees I gave. You know what north is. You know what a mile is. So if I told you to head 5 miles north you would know where to go. But only because you have been to a school/otherwise had education on this. Bees don't have that. They do a little dance which tells other bees the exact direction and distance of good flowers. How do the bees know this 'language'? Has it evolved? If so how? The queen isn't involved in this dance, and the drones all die without reproducing?

The [edit][del]drones[/del] workers[/edit] are all exact clones of each other, containing copies of one of the queen's two sets of chromosomes. Hence the colony can be thought of as a single individual, with the workers being autonomous appendages of the queen. See gene-centric evolution, below. It's literally a "hive mind," and explains, along with everything else, why bees and other social insects will so readily die in the defence of their nest; from the individual's perspective, there is no difference between her death or her twin sister's death, as her behaviour is defined by her genes and as such is adapted to propagate those genes. [edit]Communication between worker bees/ants (by pheromones, dance, or whatever) evolved in basically the same way as communication between human sense organs, brain and muscles (by electrochemical impulse), because worker bees/ants in the same colony all have the same genes just like the cells in your body all have the same genes.[/edit]

I think ants are my favourite animal for these reasons, and also because they account for between 15 and 25 percent of all land animal biomass; how's that for dominance? ;-)

Ahhh but you are falling into the same trap that others are. You are explaining why these traits are so successful now, but haven't addressed how natural selection could have brought these traits about. These animals came from others which were fiercely indepentant. It is, scientists agree (cladogram for the Formicidae is woefully uncomplete), an enigma. One of many that the natural world presents us with.

 

[oktalist]

They do a little dance which tells other bees the exact direction and distance of good flowers. How do the bees know this 'language'? Has it evolved? If so how? The queen isn't involved in this dance, and the drones all die without reproducing?

The [edit][del]drones[/del] workers[/edit] are all exact clones of each other, containing copies of one of the queen's two sets of chromosomes. Hence the colony can be thought of as a single individual, with the workers being autonomous appendages of the queen. See gene-centric evolution, below. It's literally a "hive mind," and explains, along with everything else, why bees and other social insects will so readily die in the defence of their nest; from the individual's perspective, there is no difference between her death or her twin sister's death, as her behaviour is defined by her genes and as such is adapted to propagate those genes. [edit]Communication between worker bees/ants (by pheromones, dance, or whatever) evolved in basically the same way as communication between human sense organs, brain and muscles (by electrochemical impulse), because worker bees/ants in the same colony all have the same genes just like the cells in your body all have the same genes.[/edit]

Ahhh but you are falling into the same trap that others are. You are explaining why these traits are so successful now, but haven't addressed how natural selection could have brought these traits about.

I was only trying to explain how "the queen isn't involved in this dance, and the drones all die without reproducing" does not contradict how the bees' dance could have evolved, because of the haplodiploid reproductive system and the superorganism status of the colony.

These animals came from others which were fiercely indepentant. It is, scientists agree (cladogram for the Formicidae is woefully uncomplete), an enigma. One of many that the natural world presents us with.

"Enigma" suggests it is inexplicable within the framework of natural selection, and it is not that ("it" being eusociality). Scientists might disagree about precisely how it evolved, but that doesn't mean there's an omission in the theory of evolution, only in the fossil record. Also I don't know if you can be sure about their ancestors being "fiercely independent."

The footnotes in these wiki pages cite some interesting-sounding papers:
http://en.wikipedia.org/wiki/Evolutionary_history_of_life#Social_insects
http://en.wikipedia.org/wiki/Social_insects#Theories_of_social_evolution

It certainly seems "difficult" for it to evolve, there being only very particular conditions which are favourable to it. It seems at first glance as if it would require a great leap of mutation, or for "less fit" genes to be selected for -- like travelling from the peak of one mountain to the peak of a nearby higher mountain, one must either travel downwards before going up again, or simply leap the gap like Superman. But on closer examination there may be a traversable path between the peaks under certain circumstances.

Haplodiploid reproduction is especially conducive to eusociality because a worker's sister shares more of her genes than her daughter would, if she were able to reproduce. That means it is more advantageous to her genes for her to invest in caring for her sisters, rather than producing daughters.

The modern consensus seems to be leaning towards it starting with cooperation in building defensive structures (proto-nests) which became a base from which could evolve cooperative foraging. Compare with schools of fish, herds of bovidae, flocks of birds. Incidentally another fascinating phenomenon.

 

[cuddly_tomato]

They do a little dance which tells other bees the exact direction and distance of good flowers. How do the bees know this 'language'? Has it evolved? If so how? The queen isn't involved in this dance, and the drones all die without reproducing?

The [edit][del]drones[/del] workers[/edit] are all exact clones of each other, containing copies of one of the queen's two sets of chromosomes. Hence the colony can be thought of as a single individual, with the workers being autonomous appendages of the queen. See gene-centric evolution, below. It's literally a "hive mind," and explains, along with everything else, why bees and other social insects will so readily die in the defence of their nest; from the individual's perspective, there is no difference between her death or her twin sister's death, as her behaviour is defined by her genes and as such is adapted to propagate those genes. [edit]Communication between worker bees/ants (by pheromones, dance, or whatever) evolved in basically the same way as communication between human sense organs, brain and muscles (by electrochemical impulse), because worker bees/ants in the same colony all have the same genes just like the cells in your body all have the same genes.[/edit]

Ahhh but you are falling into the same trap that others are. You are explaining why these traits are so successful now, but haven't addressed how natural selection could have brought these traits about.

I was only trying to explain how "the queen isn't involved in this dance, and the drones all die without reproducing" does not contradict how the bees' dance could have evolved, because of the haplodiploid reproductive system and the superorganism status of the colony.

These animals came from others which were fiercely indepentant. It is, scientists agree (cladogram for the Formicidae is woefully uncomplete), an enigma. One of many that the natural world presents us with.

"Enigma" suggests it is inexplicable within the framework of natural selection, and it is not that ("it" being eusociality). Scientists might disagree about precisely how it evolved, but that doesn't mean there's an omission in the theory of evolution, only in the fossil record. Also I don't know if you can be sure about their ancestors being "fiercely independent."

The ancestors of insects were indeed "fiercely independant". Bugs generally aren't known for their social skills.

The footnotes in these wiki pages cite some interesting-sounding papers:
http://en.wikipedia.org/wiki/Evolutionary_history_of_life#Social_insects
http://en.wikipedia.org/wiki/Social_insects#Theories_of_social_evolution

From those links...

The social insects are remarkable because the great majority of individuals in each colony are sterile. This appears contrary to basic concepts of evolution such as natural selection and the selfish gene.

...and...

In spite of the obvious advantages of common foraging and defense, eusocial animals had appeared paradoxical even to Darwin: if adaptive evolution unfolds by differential survival of individuals, how can individuals incapable of passing on their genes possibly evolve and persist? Since they do not breed, their fitness should be zero and any genes causing this condition should be eliminated from the population immediately. In Origin of Species (first edition, Ch. 8), Darwin called this behavior the "one special difficulty, which at first appeared to me insuperable, and actually fatal to my theory." Darwin anticipated that a possible resolution to the paradox might lie in the close family relationship, but specific theories (e.g. kin selection or inclusive fitness) had to wait for the discovery of the mechanisms for genetic inheritance.

It certainly seems "difficult" for it to evolve, there being only very particular conditions which are favourable to it. It seems at first glance as if it would require a great leap of mutation, or for "less fit" genes to be selected for -- like travelling from the peak of one mountain to the peak of a nearby higher mountain, one must either travel downwards before going up again, or simply leap the gap like Superman. But on closer examination there may be a traversable path between the peaks under certain circumstances.

Evolution doesn't make great leaps. It takes small steps.

Haplodiploid reproduction is especially conducive to eusociality because a worker's sister shares more of her genes than her daughter would, if she were able to reproduce. That means it is more advantageous to her genes for her to invest in caring for her sisters, rather than producing daughters.

The modern consensus seems to be leaning towards it starting with cooperation in building defensive structures (proto-nests) which became a base from which could evolve cooperative foraging. Compare with schools of fish, herds of bovidae, flocks of birds. Incidentally another fascinating phenomenon.

Can't compare vertibrates with invertibrates I am afraid. Especially in this case as those fish, birds, herds all reproduce. Insect societies don't.

 

[oktalist]

The social insects are remarkable because the great majority of individuals in each colony are sterile. This appears contrary to basic concepts of evolution such as natural selection and the selfish gene.

The important word there being "appears."

Darwin called this behavior the "one special difficulty, which at first appeared to me insuperable, and actually fatal to my theory."

150 years ago.

It certainly seems "difficult" for it to evolve, there being only very particular conditions which are favourable to it. It seems at first glance as if it would require a great leap of mutation, or for "less fit" genes to be selected for -- like travelling from the peak of one mountain to the peak of a nearby higher mountain, one must either travel downwards before going up again, or simply leap the gap like Superman. But on closer examination there may be a traversable path between the peaks under certain circumstances.

Evolution doesn't make great leaps. It takes small steps.

That's what I mean. At first, eusociality would appear to require a great leap, but when investigated further, it doesn't; it could evolve gradually, so there is no major mystery to how it happened, just a number of possible theories with conflicting details, none of which contradicts natural selection.

Haplodiploid reproduction is especially conducive to eusociality because a worker's sister shares more of her genes than her daughter would, if she were able to reproduce. That means it is more advantageous to her genes for her to invest in caring for her sisters, rather than producing daughters.

The modern consensus seems to be leaning towards it starting with cooperation in building defensive structures (proto-nests) which became a base from which could evolve cooperative foraging. Compare with schools of fish, herds of bovidae, flocks of birds. Incidentally another fascinating phenomenon.

Can't compare vertibrates with invertibrates I am afraid. Especially in this case as those fish, birds, herds all reproduce. Insect societies don't.

They both evolve, don't they? What fundamental difference between vertebrate and invertebrate genetics means I can't compare the two? All I'm saying is that the herds, flocks and schools show that the evolution of non-nepotic cooperative strategies for defence and foraging is fairly common. It even occurs in simple computer simulations of co-evolution. Swarms of midges and locusts, if you want some non-eusocial invertebrate examples. For the social insects, the cooperation came first, then the sterile workers came afterwards, building adaptation upon adaptation. When cooperation was evolving in these insects, they were still reproducing in the normal way, albeit haplodiploidally.

A eusocial insect colony does reproduce, through its queen; it's just the workers, who constitute the majority of its members, who don't reproduce, as reproduction would for them be less beneficial to their genes. Depending on which species we're talking about, at some point in the colony's life cycle some of its members become fertile and fly off to found new colonies and become queens themselves, having two sets of chromosomes. It benefits a queen for her to produce sterile workers to find food and defend her from attack.

 

[mikklee]

I'd have to say the big bang, I mean nothing explodes and produces everything. One teeny problem I have with it though, how does nothing at all actually explode?

That's not it. Everything was concentrated to a single point, or singularity, which then expanded outwards with a massive outpouring of matter.

There's no explosion involved.

My point still stands though, nothing somehow became everything. Originally nothing existed, at all, and somehow the universe came into existance, thats what fascinates me, not whether its exploded or not. And technically and explosion is a rapid outpouring of matter, its not always a boom