mistermack

That story is actually a popular myth.

Example?

Of course, it's not just sex cells that experience mutations. Mutations in other bodily cells can play a part in cancer etc.

That's what I thought too. But, that doesn't control the mutation rate. It just axes those mutations later, having the same result in practice. (although it would be more wasteful of embryos). Whether there is a mechanism to reduce the mutation rate could only be answered by a geneticist, or by a genetic textbook. My guess would be there is not. But that really is an uninformed guess.

Yes, I took that to be what the OP is asking about. To simplify that picture, imagine an object in a vice, squeezed as hard as it can go. The object in the middle must be supplying an equal reaction to both sides. Otherwise it has to move. And action and reaction are equal and opposite.

In my original post, I just asked what a field was. We don't know seems to be the most accurate answer to that. But to complicate it, we have two totally different ways of saying we don't know. And when you talk about one way, you mustn't mention the other. Ok, that's all new to me, so I know more now than I did at the start. I wasn't really aware of the gulf between classical physics and quantum physics on this site. You don't get any sense of it in wikipedia articles. They usually mention both, and just say, "in classical physics this, in quantum physics that". It's all there on the same page. I just followed that example, without really thinking any more of it. This is from the top of the wiki Magnetic Field page: "Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin.[1][2] In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic tensor; the split of this tensor into electric and magnetic fields depends on the relative velocity of the observer and charge. In quantum physics, the electromagnetic field is quantized and electromagnetic interactions result from the exchange of photons." It was when I read that, that I immediately wondered why we couldn't see the photons. I had to dig around quite a bit to find out that they are virtual. Mind you, the force that they produce is real enough. You would think that if they are real enough to move goods trains, they would be real enough to see. But obviously not.

I agree. The phones are a spring, and the force at one end should be the same as the force at the other.. Unless the headphones are tight to the head, then the force on one side balances the force on the other. The pressure might be different, if the effective area of the pads are different, but that's a different question.

That's a good point. But I would suspect that when a species declines, it's usually due to outside factors, rather than the way it's evolved. Unless, I guess, it specialises to such a degree that it's left vulnerable to any new conditions. Like the Dodo, becoming big and fat and flightless and delicious, because of the lack of predators on Mauritius.

That's right. Evolution has no intentions, or preferred direction. It simply follows what is advantageous in the present for billions of individuals acting as individuals. If there's a resource available, something will go for it. I believe there are bats somewhere in the Pacific that are losing the power of flight, and living on the ground like mice. (that's a vague memory, but I think it is right). So after evolving flight, they are dumping it again. Like Ostriches and Penguins did I guess. It happens because it's a success, at the time and place that it occurs.

Studiot, you come across as very condescending in some of your posts. I can only assume you are reading my intentions wrong, in posting here. You know perfectly well why I posed the question about photons. It's not a stupid question, it was just something I wanted to know. Happily I found the answer myself. But thanks for your input.

No, but just because this is the classical physics section, doesn't mean you have to ignore quantum theory. Note I said IF the magnetic force is provided by photons. But both classical and quantum physics hypothesise some kind of virtual force carrier that can't be detected. You can detect the force, but not what mediates it. By the way, why do they say "mediates" ? Is it in the sense of acting as a medium?

It's not such a simple question. A lot of communication goes on in non-conscious unintended ways. Vultures tell other vultures of food, by their sudden descent, which the others are looking for. A wolf tells the others of the pack that it's spotted a prey animal, by it's body language. Dolphins are apparently jumping to alert others of a shoal of fish, by the noise they make when they land. Mothers tell their cubs of danger just by their body language, without making a sound. Even some trees give off a pheromone that "warn's" other trees of attack by grazers etc, and the other trees respond by producing poisons. But telling other animals about food is bound to be rare, as most animals don't want to share. We humans are streets ahead of others in the communication stakes though. It's what makes us truly unique. And we needed a huge brain to do it.

The above answers are all agreed with. But it's an incredibly complicated process, as it's natural selection operating on not just a new mutation, but the millions of historic mutations, stored in our genes. Each individual has a unique selection of genes (except identical twins). So it's usually a new combination that either works or fails. New mutations are rare, but new combinations happen each time something is born. So evolution doesn't have to wait for a new mutation, it's happening with every new individual. In the case of whales, I suspect that limbs finally got the chance to be real fins once the whales evolved the ability to give birth in the sea, removing the necessity to be able to move about on land. So you have evolution in one part of the animal leading to unexpected evolution in another. It's not always obvious at first sight what has happened and why.

That's what I like about it. It must be boring, being god.

Earlier in the thread, I asked, if the magnetic force is provided by photons, why we don't see them, or detect them streaming out of a magnet. Nobody answered that one, but I'm guessing that the answer is that they are virtual photons, discussed here: So it's another "we don't know, but this works" answer. They are mounting up.

Happy-errr. One question leads to another, so I'm never happy. I said on page 2 that I was beginning to suspect that my answer was "nobody knows". And the Baden-Fuller introduction pretty well confirmed that. You don't postulate three different hypothetical scenarios, if you know what something is. The term "field" itself doesn't help, as people seem to have varying aspects as to what it means. You wrote "The field is just a catalog of the values of the field variable in some region of space at a particular point in time." I was thinking of a field as the volume of space combined with the magnetic or gravitational effects within it. Wikipedia in it's "Magnetic Field" page has as the first sentence "A magnetic field is the magnetic effect of electric currents and magnetic materials. " In other words, not a the catalog, but the actual thing that is catalogued. It was in that sense of field that I asked the question. But now one question has turned into about half a dozen. That's the way it goes I guess.

Studiot, thanks for posting the Baden-Fuller exerpt. It told me what I wanted to know in a few sentences. If the rest of the book is as clear, it really is a delightful tome.

If every bit of mass has a field that extends to every part of the Universe, is it in a similar way that all roads lead to Rome? Or all phones are connected to the White House? In other words, the field is just a reflection of the object's connection to the fabric of space time?

No, what I meant was, everything's already moving. (In all frames apart from one) So it's not a question of causing something to move, it a question of affecting it's existing motion.

I'm not sure I agree totally agree. I don't think "cause" is the right word. Affect is maybe better? My head isn't all that big. But it's part of the Earth, which gives the Sun a wobble. All parts of the Earth must be taking part in that? And the Sun gives the Milky Way a minute wobble. All parts of the Solar System must be helping? You can't exclude my head from that, surely? And the Milky Way interacts with a local group and so on. So my head makes a negligible, but non-zero contribution to how the Universe moves, I would have thought.

Yes, we agree, but I would say that most physics questions are at the point where we can still go further than we are at the moment. We have the problem of dark energy. People can see what it does, but they still are trying to find out what it IS. Not necessarily what it fundamentally is. But any progress is better than nothing.

There is a lot of evidence that new species arrive more quickly on Islands. The effect of isolation is one thing, but inbreeding can also produce fairly quick change in the island population. And from a breeding point of view, an island doesn't have to be bounded by an ocean. It can be created by deserts that are too hard to cross, or rivers that can't be crossed as well. In Africa, you have Bonobos and Chimpanzees separated by a river. (can't remember which one) And if the course of a major river changes, it can split populations and produce an "island" of population, leading to speciation. That might well have happened in the chimp/bonobo example.

I disagree. There are levels of answering. Take my example of the Sun. People used to think it was a disk that moved across heaven. Then they found it is a globe, and we moved, not it. Then they discovered it was lit by nuclear fusion. Then they measured it's composition. And deduced it's age. These are all things that tell you about what it is. There is still a long way to go, but they are all part of the answer.

So does the gravitational field of every object extend right around the Universe? Or does it stop when it's effect drops below one "quantum" of gravity?

Edit last post: Interbreeding should read inbreeding. Silly me.