mistermack

I don't get what you mean by independently. Also, what particle characteristics do you mean? You have matter particles and you have bosons. A photon is a boson, it won't have the same characteristics as a fermion.

Nor I, so don't quote me. I think momentum equals it's energy divided by the speed of light. So it's going to be tiny. But still enough to change the course of an asteroid over time, with enough hits from photons.

But in your OP you said that if something doesn't have rest mass, it doesn't exist. I don't see how you derived that conclusion. Something moving at the speed of light can't have rest mass, but it doesn't follow from that that it doesn't exist. It just means that the equations for rest mass don't apply to it. It can still have energy, and hence exist, as a result of it's momentum. Momentum that is not the product of mass and velocity, but still momentum.

As far as I'm aware, the equations of relativity relating to rest mass apply to particles at rest, ie, in the rest frame that is co-moving with the particle. I think that for a photon, there is no such rest frame available.

I'm sure that's all right. It wouldn't do to have too much variation, it would be wasteful, as in the end, males and females have one sexual job to do. It's not just genetics though. Hormones play a big part, although of course, they are the result of genetics. Young males have a different mix of hormones up to a certain age, and it keeps them on more on the feminine side. So they don't appear threatening to bigger, older males, until they are big and strong enough to either outrun the dominant males and escape, or to defend themselves against them. When that happens, the male hormones kick in, and they start showing more maleness physically, and in behaviour. And there is variation in how and when this comes about. Maybe some homosexual animals never produce much testosterone. I have no idea if that's the case, but if so, it could be due to an accident of development, rather than pre-determining genetics. Edit: of course, no amount of hormones would change a person's sexual orientation. That's been tried in the past, in vain attempts to "cure" gays. What happens in the brain to cause sexual orientation is much more complicated, and seems to be irreversible by any known means.

One important fact is that because of sexual reproduction, nearly every individual is genetically unique. This is a huge benefit to the species, as it can adapt to various changes and niches. So there is variation inherent in the species, and that extends to sexual characteristics, just like everything else. Male and Female are not fixed characteristics, males have a range of "maleness" and likewise females a range of femininity. It's an advantage. If every male had the same amount of aggression, for example, it could lead to them getting worn out in conflicts, eventually leading to a lack of healthy males. If every male had the same identical urge to mate as the others, something similar could happen. Being less aggressively male might give you more chance with some of the females, who might be scared of the more aggressive males. So if you have a range of males, it covers more situations. Some might survive and mate by being LESS male. If you have that variation, it's likely that some will vary all the way into the homosexual range of behaviour. It's a "price" of having variation, but it's well worth it.

I also think that the definition of what the original poster meant by sodomy is important. I've always understood sodomy to mean anal penetration with a penis. But the OP seems to be talking about homosexuality. Not the same thing at all, but linked. You can be homosexual without ever engaging in sodomy, and you can sodomise without being homosexual. Sodomy itself would appear to be easy enough to understand. Males don't need to be too fussy when they mate, in many species. If they get it wrong, it doesn't have much of a cost. But if they miss a chance of mating by hesitating, another male might get in before them. So it pays to mate first, and check later. Many males will mate with something that bears only the slightest resemblance to a female of their species. The urge overrules almost everything. Homosexuality is harder to explain. But the answer is probably mainly that nothing is perfect in nature. And we have vestiges of our earlier ancestors remaining that are hardly noticeable. Like the human remnants of a tail, or the appendix. Our distant ancestors were originally hermaphrodites, and homosexuality could be a throwback to that type. From an evolutionary point of view, the disadvantage is only there in the most extreme cases. Lots of male homosexuals have plenty of children, and of course lesbians in a wild situation might well get mated, whether they wanted to or not. So the disadvantage to the species would be very marginal. There is also the fact that in humans, non-fertile members play an important role in child protection and care. Females live on well past their menopause. They help raise the young, and contribute to the survival of the species, even though they can't have any more offspring themselves. That might well apply to the homosexual humans who don't produce young of their own. Humans evolved living communally in extended groups, like chimps. And child care is more extended in humans than any other animal. So non-breeding individuals can still help their own genes to survive in nephews and nieces etc.

It's difficult to police, so we tend to ignore animals "below" the level of rats. I don't see that changing much in the near future. What's also interesting, is how we treat machines with artificial intelligence. If it's morally bad to mistreat an ant, then isn't it just as bad to mistreat a machine that is far advanced of the ant in every way? Maybe it depends on whether the machine has been given a sense of personal identity, and a desire to keep existing. What would it be like to say to your computer, "I'm scrapping you, because I've bought the new model". I already feel bad about scrapping my car. And it doesn't speak to me or interact. What if people in the future chat to their cars all the time? ( with the car doing the driving) You might feel really bad about scrapping it.

I remember reading recently that the Sun has a magnetic field. Apparently it's been twice as strong as normal over the last 100 years. Some Danish scientists are making the argument that the Sun's magnetic field deflects cosmic rays, so when it is strong, we get less of them. And the argument goes on that cosmic rays help to seed low level clouds, and low level clouds are strong reflectors of solar energy back into space. So the recent global warming could be due to the currently strong solar magnetic field, (and hence less low-level cloud) and less due to CO2 levels. I don't want to divert the discussion, I just thought it was an interesting addition. The Sun's magnetic field flips every 11 years, whereas the Earth's flips over millions of years. I have no idea what the mechanism is, but in the case of the Sun, it doesn't seem to make a lot of difference.

If sound is the transfer of energy physically from particle to particle, across a distance, then I suppose it can travel in space. Sound in a solid is fairly simple, as the bonds between particles are fairly fixed. Sound in a gas would be more complicated, depending on the concentration of the gas. If you think of space as a gas, the concentration is so low, that the particles would not have a bond with the next particle, at the instant that the sound arrived. It's motion would be affected, and that could eventually affect another particle, so some sort of transfer of energy could occur as a wave, over a long period. But I doubt if you could call that sound. Maybe it would be wrong to call it sound, when the gas is so dispersed that each particle does not have at least one physical link to another, at all times. All just my musing speculation, as usual.

It is a bit circular in nature. Faster than light communication causes a nonsense result, when put into relativity calculations. But relativity is based on nothing going faster than light. So IF faster than light messages were possible, the nonsense result would itself be suspect, as it's derived using a system that clearly would have a flaw somewhere in the current version. Having said that, I wouldn't be betting much on anything like that being the case.

I vaguely remember something about time travel being made possible by faster than light messaging. According to relativity, you can receive an answer to a message that you haven't yet sent. ( if I recall it correctly ). As this is clearly impossible, either the faster than light messaging will always be impossible, or relativity has a flaw in this regard. My memory is a bit hazy about the details but I'm sure others on here will be aware of it.

No you didn't. You knew what was meant but get a pleasurable little kick out of contradicting people. I certainly don't begrudge you those little moments if it makes you happy.

My meaning should have been clear from the context. It was to Tim88. I didn't write angular acceleration, and the fact that I wrote that it could continue for ever without energy input should have made it perfectly obvious what I was referring to. Seems more like a case of deliberate misunderstanding.

How rigid does it have to be, to need an energy input?

Good lord ! I had no idea !

Gravity doesn't have to be directed radially inwards though. On a non-rotating planet, it would be a constant force in a constant direction, as in the elevator in space. One big difference in rotational acceleration, compared to linear acceleration, appears to be how energy is involved. No external source of energy is needed for a constant rotational acceleration. It could continue for ever without any input. But to accelerate a mass in a straight line, you need to put in energy, in greater and greater quantities as the speed increases. In one case the forces are just re-directing the velocity. In the other, they are increasing it. Gravity seems to be a cross between the two. The feeling of acceleration without the need for energy input, or any change of direction.

Travelling in a circle is a different kind of acceleration though. It's not continuous, but constantly changing in direction. More of a series of infinitely small accelerations, all in slightly different directions. Unlike the effect of gravity which is constant in magnitude and direction. The first wouldn't result in encountering the speed of light barrier whereas a constant acceleration in a straight line would.

I agree with all of that. One thing that I don't agree with though, is the often posted claim that science is just about modelling, and accurately describing and predicting the world. Newton and Einstein would have LOVED to discover what causes gravity, rather than just modelling and calculating what it does. (I don't mean "just" in a derogatory way) The actual mechanism was not detectable to them, as it's still not identifiable now. The similarity between acceleration and gravity I find fascinating, and I think is probably a strong clue to the actual mechanism. But the differences are also substantial, as in the problem with reaching the speed of light, if you were to have a constant acceleration, whereas you don't, on the surface of the Earth, even though it feels exactly the same. You can model it by imagining an accelerating reference frame, but that only makes sense for temporary and local events. If each bit of mass in my body had a spring attached to it, connected to the centre of gravity of the earth, you could model the effect as curved space time and accurately predict the motion if I jumped up and down. But if the spring was in plain sight, you would concentrate on that.

Maybe Janus works on the theory that if you don't use it, you lose it. I should know, I lost it years ago.

Thanks, I get what you are saying there. One question that occurs to me though, is can an accelerating frame of reference be real? I can see how it works locally and temporarily, but as far as the Universe goes, it would mean that the total energy of the Universe is constantly rising. So I can picture an accelerating reference frame, no problem. But can one exist, other than as a local effect? If you take it to it's logical conclusion, an accelerating reference frame would have everything in the Universe moving faster than light eventually. Or, on the elevator, a constant acceleration of 1g would take you past the speed of light.

That's fine, except that I keep reading that gravity isn't a force. That's the essence of what I was saying really. It's not a force, it's curvature of space time, needing a real force to counteract it and stop me from following it. But it's not acceleration either, because I'm not gaining kinetic energy.

Yes, I get that. But the difference is, in space you would be going faster and faster as a result of the force. Here on Earth, the same force keeps you stationary. Obviously, I'm not following the natural curvature of space time by remaining at the surface of the Earth, so I accept that that's what's happening in GR. But in the space elevator, I'm gaining kinetic energy. Here on Earth I'm not. Which makes me think it's not an exact match for acceleration.

My limited understanding of general relativity is that it describes very accurately the way things move under gravity. With no gravitational effect, things move in straight lines, and it takes a force to accelerate them in any direction. Under GR, gravity isn't a force, but a curvature of space time. Seeing as there is no detectable force carrier, that's a good model to use. But if a force carrier is found, like the graviton, will GR then become like Newton's laws, an excellent working model, but not the definitive answer? What bothers me about GR is that the force I feel pulling me to Earth is supposed to be indistinguishable from acceleration. But the big difference that find is that, if I am feeling acceleration at 9.81 metres per sec², I should have passed the speed of light years ago. So with gravity, it seems to flip. In remote space, you need force to go faster. In a gravitational field, you need a force to stay still.

I've tried and failed to improve my nails for finger picking, so this is good stuff and thanks for the pointers. It sounds like it's a mistake to use the glass file on the left hand though, but I'll definitely be trying it on my right hand. I've tried all sorts including false nails and various lacquers, nothing really worked for me. I find it odd that some nails are much stronger than others. My little finger nail is by far the best, and it gets the same minerals as the others.