mistermack

I don't think it falls out of that, that any observer will get the same result, regardless of their motion. It says that the speed of light will always be the same, that's all. You could give the speed of sound the same treatment. But different observers will get different figures.

Well, when you ask such a generalised question, you get a generalised answer. Each species has it's own history, it's own niche and it's own strengths and weaknesses. If you want to know why there are so many more now, with hard inner skeletons, then it's down to what those skeletons do. For the most part, it's the obvious answer. They act as levers, enabling more rapid motion, and also give stronger support than just muscle. You only have to look at your own legs, and picture what they would be like without bones. The answer IS pretty obvious. And always has been. And that's why it's not new.

Looking again at some of the pictures, it seems likely that the rocks that are visible are volcanic tuff, rather than basaltic flows. That would explain the obvious layering that you can see in google earth. The Siberian Traps event went on for about a million years, and there are large areas of tuff in the area, according to wikipedia. Tuff is an ash deposit, which becomes solidified as the rain turns it to mud, and more layers are deposited on top. Tuff is a soft rock, so weathering is fairly rapid, So the "towers" of harder rock were probably buried during the last ice-age and exposed more recently by weathering.

What makes you think that the true answer to your question should be new and non-obvious?

Isn't it because of time dilation that the speed of light is a constant? If you accept that two different observers travelling relative to each other experience different elapsed time, for the same measurement, then even though they observe different distances, they also measure different elapsed time. And because the speed of light is intimately involved in the time dilation, the difference in distance is always exactly negated by the difference in time elapsed. So the ratio of distance over time for light has to be the same for both observers. I'm not a mathematician, but if you have the formulae for time dilation, can't you prove that any and every observer will always get the same value for the speed of light? Of course, you're then making assumptions for time dilation, or going on the experimental results I guess. One way or another, you have to propose something first, and then verify it with experiments.

Yes, I thought of that. But change in position relative to what? Obviously not the space around the object. Is there some fixed set of coordinates that an object is stationary in? If space in a gravitational field is curving with time, what frame of reference is there that is independent of that? If there was a master frame of reference, that everything moved relative to, that you could get a fix on, it would all be a lot easier to picture.

I like that better than the rubber sheet. It's very good. But it's carefully phrased at the end. That's "HOW" gravity makes things fall. It describes it well, but it doesn't say "why" things fall. It sort of transfers the question. Instead of "why do things fall?" you now need to know, "why do things want to go "straight" when the orientation of local space is constantly changing? Why don't massive particles follow the orientation of the local space, as it changes with time? So exactly the same question remains unanswered, it's just been transcribed.

The answer to the original question is just a matter of evolutionary history. There were plenty of soft-bodied swimmers in the sea at one time. Some are still around. Look up hagfish and lampreys. And sharks and rays have a less hard, cartilage skeleton. It just so happens that others evolved bony skeletons. Many also evolved bony armour. Especially in the past. Most species that ever existed are now extinct. What we have now are the lucky ones, that always found a niche for themselves as they evolved. The bony fish were the ones that first dragged themselves onto land, and became amphibians. You would think that having a harder skeleton for the fins to lever against helped make locomotion on land more efficient. But it might be that they just got there first, and got a head start on all of the others, which proved decisive. Animals are the way that they are because their ancestors found ways to survive and resist extinction. Marine worms are a success in their own way, just as elephants are. Things don't have to be bony, but in some circumstances, it has been a success. But there is no rule about it. Hagfish have been more of a success than most bony fish. Because they are still here, and most bony fish species have gone extinct.

I've never liked the rubber sheet picture. I don't think it reflects the reality of 3D spacetime distortion. To understand gravity you need to understand what mass is. And what energy is. Since we're not there yet, we have to make do with models that can represent what's happening accurately, so that we can calculate what will happen. But they are still just models. My own mental picture is that a massive particle is just a huge amount of wave energy, rotating around itself in a tiny spherical ball. When it's in a gravitational field, spacetime is pulled out of it's natural symmetrical shape, and the ball becomes slightly unsymmetrical, in the direction of the object causing the field. A bit pear-shaped. So the wave isn't following the same curve everywhere any more. And it's the lack of symmetry that makes the whole thing want to accelerate in the direction of the mass causing the gravitational field. That's my mental picture at the moment. It's sure to be bollocks, but it keeps me happy till I hear one I like better.

A subject that came up recently in another thread. Why do humans suffer so many miscarriages of pregnancy? Is it down to genetic abnormalities? Is there a checking mechanism responsible for this? Have any studies been done? How do humans compare to monkeys and apes? Do other mammals have the same problem?

With all of the answers on this thread, I'm firstly wishing I'd been more specific in the original question, and asked what is a gravitational or electromagnetic field, since the word field gets used in different ways. As to those two, what I'm getting is that a gravitational field isn't really one thing. Since it extends to infinity, we are really in billions and squillions of fields, of every bit of mass in the universe. So in theory, we are in one super-complicated field. In practice, a lot of it is negligible, for calculation purposes, but it's still there. We are in the Earth's gravitational field, and Earth is in the Sun's. And the Sun is in the Milky Way's field, and the Milky way is in the field of the local group and so on. The picture I'm getting is of a 3D spider's web, with every bit of tension, at any point, having an effect on the shape of the rest of the web everywhere you look. And if the spider's web was a km in diameter, it would take a finite time for any change at one end to have an effect at the other. Which is similar to gravity effects travelling at the speed of light.

We also have other reasons why our pelvis is different to that of other apes. Walking upright, our organs are stacked in a column, and need support from below. You can see in the fossils of our ancestors how the pelvis gradually changed with upright walking to something wider and flatter. Then, when our brains got bigger and bigger, that also had an effect on the pelvis, as the baby's heads got bigger, requiring a bigger birth canal. If you combine all that with our extra fat and two-legged locomotion, it all explains the bigger ass.

Nicely put.

The question really is, "why is our ass different to a chimp's, or gorilla's?" since seven or eight million years ago, our ancestors asses were similar to those. Well, it's not for sitting on. You only have to look at people like bushmen, who don't use chairs, to see that. They squat on their haunches with the ass off the ground. You will hardly ever see them sitting, like we all do. So I'm sure it didn't evolve as something to sit on. When you walk on two legs, you need a bit of ass muscle to move along. It could be the mechanics of upright motion that demands a bigger ass. Then you have the fact that we have more fat on our bodies than other apes. Presumably, if you spend a lot of time in trees, the extra weight of storing fat is a liability when you fall, or when you support your weight with thin branches. And your strength to weight ratio is poorer, if you have a store of fat. So fat is not good in the trees. But not so bad on the ground. It can tide you over hard times, and help mothers produce milk. And the ass is a good place to put some of it.

Some birds of prey can detect light frequencies that we can't. I think it's into the ultra-violet range. Because a lot of rodents have regular runs, and pee as the go, they eventually leave an ultra violet trail that the birds can pick up on. (that's from memory so it might be off the mark) Other rodents actually wear little paths on their regular routes, (like cattle do) which are easy for the birds to see from the air. So the birds know where to look from the tracks. Whether you can call that tracking is debatable.

It seems that all the articles say something similar. It seems to be a generally accepted estimate that about half are caused by chromosomal abnormalities, although whether that's the result of proper studies, or just a general opinion is unclear. You would think that studies would have been done on this subject, but after looking at Google search results, they all seem to say that about half of early miscarriages are gentetic, but nobody mentions how they know that. Maybe it's considered obvious, from looking at the fetus. Or maybe studies have been done, but nobody is quoting them. It seems to be a high failure rate, but maybe, considering the dangers of childbirth, it's an evolutionary sound method of protecting a mother from the dangers of going full term, just to produce a baby that is not viable long-term Humans have just about the most dangerous childbirth of any mammal, due to the size of our heads, so maybe screening embryos in the uterus evolved giving a positive survival benefit. It would be interesting to see how we compare to chimps or gorillas.

Is there any evidence that miscarriages are the result of genetic problems? It seems to be a logical thing to happen, but is it actually a fact? I've seen lots of accounts of miscarriages and babies born dead, which were described as perfectly formed, and lots of living babies are born with genetic problems. Maybe the miscarriages DO act as a checking mechanism, but I'd like to see the evidence, before being convinced.

I'm guessing you would run into problems using air. It's not very energy efficient compressing air to the sort of pressures that exist at the bottom of the ocean. My idea would be to adapt a ship to pump a jet of water at the bed, stirring up the silt, and then suck it up to the surface with another pump. You only have the friction in the pipe to overcome, so it shouldn't be too costly in energy. You could maybe use wave motion to power the pump.

Isn't it more likely though, that an extra arm, as in the linked article, was the result of an egg that started to split into identical twins, but never quite made it? As in the case of conjoined twins. Rather than being a mutation that added an extra arm.

I'm quite sold on that. I've always felt that there's huge potential in the oceans, as most of the ocean areas are literally unproductive desert, due to lack of nutrients. The main problem would be getting the nutrients there, and keeping them there, in the areas with low nutrient levels. I favour stirring up the ocean floor, and pumping the cloudy water up to the surface. Ocean storms would also be a problem. But if people are doing it now, and making money, then that is the proof of the pudding. What if it took off in a big way? Would we end up with too little CO2 and too much oxygen? You never know !

Shudder. Wish I hadn't seen that. But there's enough for a whole new thread there. Is it genetic? Is there a history of extra arms in the family? Will his kids have extra arms? I have no idea, but I'd like to know. Can a species suddenly evolve extra limbs as quick as that? Looking at the world, there seems no sign of it, so maybe it doesn't work. I'd love to have an extra one, whenever I'm working on something. But looking at him, maybe it wouldn't be worth it. He's lucky. 20,000 years ago, he would probably just get bullied to death at a very early age.

Yes, I'm not saying that we don't lose embryos. Really, I'm just saying that because we invest so much in our young, we are probably among the 0.01% of organisms who can afford it least. We think we are a successful species, but in the stone age, there were probably only about a thousand humans in the whole of Britain, so it's a very recent thing that we started to succeed in larger numbers. Yes, we could still afford losses, just, but an error checking mechanism, if it were possible, would probably benefit humans more than almost any other living things. Compared to a Carp, or an Oak tree, or a Coral or Crab, we reproduce incredibly slowly. The thing is though, that even if something would be beneficial, it doesn't necessarily evolve. There has to be a mechanism, and the feature has to have a benefit all the way from primitive to evolved. Otherwise it won't happen. I'm sure a third arm and hand would be a fantastic benefit to humans, but there's no route for it to happen. It might be the same with differential error checking.

I just noticed how I spelt wikipedia !

The first part of the popular myth is that it's spelt catastrophy. For the second part, this is from wikepedia : " Historical inaccuracies[edit]Many popular histories of physics, as well as a number of physics textbooks, present an incorrect version of the history of the ultraviolet catastrophe. In that version, the "catastrophe" was first noticed by Planck, who developed his formula in response. In fact Planck never concerned himself with this aspect of the problem, because he did not believe that the equipartition theorem was fundamental – his motivation for introducing "quanta" was entirely different. That Planck's proposal happened to provide a solution for it was realized only later, as stated above.[4]Though the true sequence of events has been known to historians for many decades, the historically incorrect version persists, in part because Planck's actual motivations for the proposal of the quantum are complicated and difficult to summarize for a lay audience.[5]"

The question should really have been posted in the genetics section. This section is evolution, morphology and exobiology. You would need to know the mechanism of proof reading, to be able to give an informed opinion, on whether some areas could be scanned more or less. The new genes are obviously checked, for repair to happen at all, so it's definitely feasible. I don't agree, Bender, that embryos are so expendable. It depends on the organism, and the point at which they fail. If it were a human, and they failed at the reproductive stage, that's a huge wasted input from the mother and extended family, giving birth and raising a child, all for nothing, in purely reproductive terms. Even if the faulty mutation just caused a miscarriage after 8 months, it's still a big cost for no reward. But to an Oak tree, one lost acorn is nothing to worry about.