Janus

Nothing. The Photons don't interact at all. This is known as pair production and the result is a particle and antiparticle (electron and positron for example). This can only happen if the combined energy of the photons is great enough to account for the mass of the particles and when a nucleus is involved. You need the nucleus to act as sort of a mediator for the pair production.

Sorry, but you'll be in for a long wait. All these "sounds" were dubbed onto the videos after the fact. They were lifted from the sound track of a movie. If I remember right, it comes from the last "War of the Worlds" movie. One giveaway pointed out in one of the videos I've seen is that any people that happen to be shown in the video never react to the "sound". No one looks up or looks like they hear it at all. Neither are there any reports besides the videos that supposedly recorded it of anyone hearing the sounds. So here's what happens: Someone makes a few of these faked videos and puts them on the web. Other people, seeing the videos figure out the hoax and decide they want to play too, and dub the sound onto their own video and put it on you-tube. Another giveaway is that in many of the videos not only is the "sound" exactly identical, but so is the background noise. You hear the same birds at the same time in the videos.

I'm pretty sure that he is referring to a scene in the latest Star Trek movie in which they show some Vulcan children in what is apparently some type of educational environment. So in essence he is asking whether something shown in a work of Science Fiction, involving an entirely imaginary alien species, has any basis in fact.

What? "My Mother, the Car" didn't make the list?

No, what happened in post #37 is that you made claims based on what you thought was true. However those claims are based on a misconception of the nature of gravitational time dilation on your part. gravitational time dilation has absolutely nothing to do with the type of clock used. Neither is it due to the strength of the local gravity. This is something that you have been told repeatedly by many different posters, but they might have as well be talking to a wall for all the good it does.

Estimates of the iceberg put it at ~50-100 high and ~200-400 ft long. However, remember, that represents only ~1/8 of the mass of the total iceberg.

I remember a while back a theory that is was weak rivets that caused seams to pop that led to the quicker sinking. If that was the case, I don't think a head-on collision would have made any difference. The shock would have still popped rivets and opened seams.

Yes it is. Whether is is a permanent magnet or a current carrying coil, it is all electromagnetism. Electric and magnetic fields are not separate things, they are two aspects of one thing. It is just unfortunate that we happen to use the term "electromagnet" for a particular type of device in order to distinguish it from a permanent magnet and use "electromagnetism" for the science that describes both.

Another thought is that is that when you hold the gun upright, the effect of recoil on the gun would cause a torque that tends to lift the barrel. This is then offset by the drop of the bullet. The two effects tend to compensate each other. When you hold the gun sideways, this same torque kicks the barrel to the side, shifting the trajectory of the bullet in that direction. Add that to the weaker grip and you'll tend to shoot wide.

Enthalpy is correct. You can't use the Earth for a gravity assist for an object that starts out with the same orbital velocity as the Earth. A gravity assist is more or less like an elastic collision, with gravity as the mediator. Here's an idealized example: Assume that you launch a probe from an inner planet to an outer planet. It's orbit is such that its aphelion is at the planet's orbit. When it gets there it will be moving much slower than the Outer planet. We assume that we time things so that the probe arrives so that it is just a bit ahead of the planet. For arguments sake we'll say the the probe is moving at pro-grade 5 km/sec and the planet at 11 km/sec. This means that the probe is moving at 6 km/sec retrograde with respect to the planet. As the probe falls in toward the planet it picks up speed. We will also assume that the probe takes a parabolic orbit around the planet, meaning that it will leave the planet at the same speed that it came in at but in the opposite direction. When the probe reaches the distance from the planet where it was originally moving at 6 km/sec retrograde wrt the planet, it is now moving 6 km/sec pro-grade. It's orbital velocity wrt to the Sun is now 11+6 = 17 km/sec, whereas before its was 5 km/sec. It has picked up 12 km/sec. Notice that 12 km/sec is twice the difference in velocity. Now imagine that the probe started at the Lagrange Point for the planet. It starts off with zero velocity difference wrt to the planet, so it is moving at 11 km/sec. It falls in toward the planet, does the parabolic orbit and climbs back out. When it reaches Lagrange point distance again, it will be moving at 0 velocity with respect to the planet, and once again is moving at 11 km/sec. It has gained no velocity with respect to the Sun.

We already have an example like that, it is called the Bullet Cluster. It is the collision between two galaxy clusters. Remember what I said about what happens when normal matter collides? It radiates heat and loses kinetic energy. So what happens with the Bullet Cluster is that the visible matter is slowed down a bit after the collision. The dark matter doesn't however and retains its speed. It is, in essence, "knocked loose" from its parent cluster We can map DM by looking for its "gravity shadow". Its mass causes gravity lensing and distortion of the light passing through and around it. So when we look at the Bullet cluster, we would expect to see a gravity shadow that is offset from the visible mass. (you should see two gravity shadows, one for the visible cluster, and one for the DM that has been knocked loose.) This is, in fact, exactly what we see. One gravity shadow surrounding the visible matter and a second one offset from that with no associated visible matter. The Bullet cluster is the closest thing we've seen to being direct evidence of DM, and is a nail in the coffin of purely modified gravity alternatives. (That's not to say that a modified theory of gravity is completely off the table, but that any such theory would have to include some type of dark matter.)

Sounds like lens flare. http://en.wikipedia.org/wiki/Lens_flare

That statement from Wikipedia is a Generalization which is not always true. For example, the Moon is closer to the Earth than the Sun is, yet the Sun exerts a greater influence on the Earth than the Moon does. In matter of fact, the Sun also exerts a greater influence on the Moon than the Earth does in terms of the Moon's path around the Sun. The Sun may be 400 times further away, but it is also 330,000 times more massive. 330,000/400^2 = ~2, meaning that Sun exerts twice the gravitational pull on the Moon than the Earth does. As far as your claim that there are nearby(closer than Alpha Centauri) stars that we've yet to discover, that is laughable. We can presently detect a star 1/100 the mass of the Sun that is 40 ly away. To suggest that that there are stars closer than 4.3 ly that we haven't found is just silly. "ordinary" matter bunches up much easier than DM for the very reason that DM is "Dark". If you have a number of normal matter particles milling around they will bump into each other, doing so creates "heat" which is radiatied away. this leaves the matter with less kinetic energy which make it more subject to gravitational collapse. Closer bunching causes more collisions leading to more heat loss, leading to tighter bunching, etc. DM On the other hand does not interact electromagnetically. It does not collide with itself or other matter. Neither can it emit electromagnetic radiation in order to bleed away energy. It only interacts gravitationally. Close encounter with other matter can cause it lose energy via gravitational radiation, but gravity waves are much much less energetic than electromagnetic wave, so the process of forming "clumps" it much much slower. Thus it has only had enough time to collapse into the much looser Dm halo, while the visible matter has collapsed to the smaller disk.

The BH only masses about 4 million solar masses. We know this by the periods of stars that orbit closely around it. But even if we to assume that it was massive enough to account for the Sun's orbital speed, it wouldn't account for the flatness of the rotation curve. If all that mass were concentrated at the center, the orbital speeds of the stars would pretty much drop of by the inverse of the squareroot of their distance from the center. What we see instead is that the orbital speeds remain close to the same as you move out. This means that the extra mass must be more or less evenly distributed. (so that as you move further away, the amount of mass you are orbiting increases.) Black holes can capture dark matter, it is just not as easily a "normal" matter. As normal matter circles a BH, it collides with other matter causing it to radiate away some of its energy, causing it to fall in closer. DM doesn't react with itself or other matter this way. So it holds on to all of its original energy. The other factor is that while 80% of the Galaxy's mass is DM, is spread out into a much larger volume than the visible disk of the galaxy. Imagine the galactic disk as being imbedded in a spherical "ball" of DM that is much larger than it is. This much larger volume means that, in any given part of the visible disk, the density of DM is much less than visible matter (This also explains why 80% of the Solar system isn't made of DM).

And This is exactly why your idea falls apart. Let's take a closer look why: The nearest star to the Sun, Alpha Centauri at 4.3 ly. So this is the individual star that would have the strongest gravitational effect on the Sun Now the Sun is ~2/3 of the way,about 27,000 ly, out from the Galactic center. Using your own estimate, there are 400 billion stars in the Galaxy. If we are conservative, we will say that 40% or 160 billion of them are closer to the center than the Sun is. Now it turns out, that if you add up all the individual gravitational gravitational attractions to the Sun of all those stars closer to the Center, The net effect is the same as if they were all bunched together at the center of the Galaxy.(Another thing Newton taught us). Thus is is the same as having the mass of 160 billion stars located 27,000 ly away. This is 6279 times the distance to Alpha Centauri. If we want to compare the relative gravitational pull of Alpha Centauri compared to all these other stars, we 160 billion and divide it by 6279² (39426717) this gives us 4058. This means that the net gravitational effect from these stars is 4058 times more than the gravitational effect of the nearest star. So here's the point: It is this net pull of all these stars that should hold the Sun in its orbit around the galaxy. The thing is that this isn't enough by quite a bit to hold the Sun in its orbit for the speed its moving. Adding the tiny bit represented by the pull of Alpha Centauri wouldn't make a bit of difference. But here's the kicker to even add Alpha Centauri's gravity, it would have to be closer to the center than the Sun, in which case, its gravity is already included in the total pull we've already calculated . So we can't add it again. The simple fact is the Scientists already know how to add together the effect of all the individual stars and the galaxy as a whole, and when they do, there just isn't enough "visible" matter to hold it together by a very large factor. You have not come up with an explanation that does away with dark matter, partly because the effect you rely on ( the mutual attraction between close stars) is just way too weak to have any real effect on the rotational speeds of those stars.

You are misinterpreting what they meant. In this case, "Older stars are less metallic than younger ones" is akin to saying the "Older people are more likely to to have driven a stick shift than younger people". It does not mean that people drive stick shifts more as they get older, but that stick shifts were more prevalent when people who are older now learned to drive. In the same way, Older stars are less metallic because when they first formed the universe as a whole was less metalic. You need to take the whole context in which the statement is made. To wit, from the Wikipedia article: Note the "may" in the first sentence, and then the later statements that indicate that the low metallicity is due to when the stars formed and the amount of metals available for them at that time. At no point do they claim that stars become less metallic as they age.

The Moon moves outward due to tidal interaction. The Moon creates a tidal bulge in the Earth and friction between this bulge and the solid Earth leads to an exchange of angular momentum. There are two reasons that this doesn't work for stars orbiting the galactic center. One is that these stars are evenly distributed around the center, thus they cancel each other out when it comes to forming a tidal bulge. The other is that the galactic center is not a solid body. Even if a bulge formed, there would be no friction between it and the center. Ergo, the mechanism that leads to the Moon's recession does not come into play with stars orbiting in the galaxy. Mars was able to maintain a higher temp and liquid water because it used to have a thicker atmosphere. This in turn was due to the fact that it used to geologically active. This has two effects. One is that such activity tends to out gas, supplying gasses to the atmosphere. The other is that it allows for the dynamo effect that produces a magnetic field. The magnetic field shields the planet from the solar wind that tends to strip away the atmosphere. Mars, being a much smaller body than the Earth, cooled faster. When its lost it interior heat, it quit adding to the atmosphere and it lost its magnetic shield. The solar wind stripped most of the atmosphere away, leaving Mars as it is today. There is no need for it to have been closer to the Sun. No, we might not, both of your examples are based on erroneous assumptions.

First off, where did you get the idea that Gravitational time dilation requires light clocks? All clocks are equally subject to gravitational time dilation. In fact, the best clock for the demonstration of gravitational time dilation would be the "ideal" clock, or a clock which is not effected by local conditions and is 100% accurate at all times. It doesn't depend on g. The difference in time rate depends on a difference of gravitational potential. For example, Take two identical clocks, place one the surface of the Earth and the other on the surface of Uranus, and arrange for them to be in identical environmental conditions (temp, pressure etc.) with the sole exception of g force. The clock on Uranus will run slower. However, the actual g force on the surface of Uranus is less than that of the Earth. The clock experiencing the lower g force will run slower. And I'll repeat, gravitational time dilation does not depend on the construction of the clock. Nor does it depend on local conditions. This is what separates it from effects such as the local g force which is a factor in the operation of a pendulum clock. Once again you have shown that you have failed to grasp the concept behind a Relativistic effect and turned that failure into a perceived flaw in the theory in your own mind.

Not at all. Let's assume that each set of clocks has an identical accelerometer with it. The ground floor pendulum notes that the reading on its accelerometer, when plugged into the pendulum equation gives an answer that matches its measured period. However, when it checks out the 50th floor accelerometer and its pendulum clock, it will note that the measured period of the clock will be less than that predicted by its accelerometer and the pendulum equation. The difference equates to the same factor as due to the time dilation measured by the light clocks. In other words, the pendulum clocks are effected by both the difference in local g and gravitational time dilation. Any type of clock placed on the 50th floor will be effected by gravitational time dilation when compared to the ground floor clock regardless of any other factors that might effect it operation. If I make two wind up clocks and design one so that it ticks half as slow as the other when they run side by side, and then put the slower running one on the 50th floor, it will now run just a bit faster than half as slow as the ground clock. Gravitational time dilation is not due to any "physical" effect on the clocks, it is due to how the measurement of time and space itself behaves. If I were to place two identical clocks in a uniform gravity field (one that does not change strength with height), the clock placed higher in the field would still run faster, even if though the g forces and every other physical influence acting on the clocks are exactly the same.

How so? A Christian is some who professes to following the teachings of Christ. So all we have to do is see what Christ had to say on the subject of homosexuality, which is nothing.

0.000...1 approaches zero as a limit, but cannot equal zero the way that .999... equals 1 It requires that there be a final "1" in the series and this always causes the number to be just a bit larger than zero. For the same reason, 0.999...9 does not equal 1, because 0.999...9, is not equal to 0.999... 0.999... does equal 1, but 0.999...9 does not. In turn: 1/0.000...1 does not equal infinity but instead 10000...0, some arbitrarily large finite number. Again, 10000...0 is not the same as 10000... 1/0 is undefined, no matter what you seem to think.

Here's the problem: A gas compressed to the point where it is just about to turn liquid will be as dense as the liquid. For example, liquid nitrogen has a density 80% of that of water. Gaseous Nitrogen compressed to the point of almost being liquid would also have a density 8% of that of water. This means that a column of nitrogen compressed to this degree would only have to be 12.5 meters high to weight the same as a column of equivalent cross-section consisting of air, at a uniform pressure of 1 atm, with a height of 8.5 kilometers. Put another way, the pressure differential between the top and bottom of your pipe will be much greater than that in the atmospheric pressure outside the pipe. You'd ened up with an "almost liquid" liquid gas at the bottom and a not so much so gas at the top. A couple of quick mentions of other problems I see You don't seem to be taking into account The latent heat in going from liguid to gas and back. Compressing the gas is not enough (mere compression just creates a Hot high pressure vapor), you also have to let the latent heat escape. At the other end, it will take an input of energy to get the liquid to change to gas. Also, how do you empty the tanks? As a liquid, they are in just a bit smaller volume than they would be as a high pressure gas. this means that the volume of the pipe can only be equal to the difference between the liquid and gas volume. Remember, when you open the valve between the two the resulting gas fills both the pipe and tank. This means that the vast majority of the gas remains in the tank, and only a small percentage bleeds into the line.

Hey, you can allect him all you want if that's what you want to do. What are you planning to use to entice him?

To start off, your spaceship could not travel at the speed of light, as material objects are restricted to travel at speeds less than c. I'm not sure that you are quoting the documentary quite right. If the spaceship travels to a planet 10 ly away (as measured by the Earth), then if it is traveling at almost the speed of light, it will take ~20 yrs to make the round trip as measured by the Earth. The occupants of the ship will however measure a much shorter trip, aging very little. From the Earth's perspective, this is because time on the ship ran slow during the trip. For the ship this is true because, for it, the distance between Earth and the planet is much shorter than 10 ly. Clocks and rulers moving relative to each other measure time and distance differently. This is why I prefaced the above statement of the distance to the planet with "as measured by the Earth", as the distance between the two i is different as measured from the spaceship. Now the documentary could have meant that the planet was 10 ly from Earth as measured by the Ship, in which case, the distance could have been ~500 ly as measured from the Earth, making the ship trip duration 20 yrs and the Earth trip duration 1000 yrs, however, I doubt it. Doing so, without being very clear about it and making mention of the difference in the distance as measured by Earth and Ship would have been unnecessarily confusing. The effect you allude to when talking about the outbound trip being long and the inbound one being short is due to the Doppler effect, which is separate form the Relativistic effect of time dilation which the example is discussing. The time dilation effect is what is left over after you account for the Doppler effect. Most times when discussing Relativity, when someone says something along the lines of " the Earth Sees, or from the perspective of the Earth, etc. They mean after any Doppler effect has been accounted for.

The shields are not the issue. The issue is that such a probe simply couldn't lose enough speed by aerobraking, and definitely wouldn't be making tight turns around the Sun. Look, your probe is moving at ~90,000 km/sec. In order for it to stay in the Solar system, it has to get its velocity down into the range of 10's of kilometers per second. If you don't do this in the first pass through the solar system, there won't be a second pass. And as I mentioned in my last post, even if all the planets were perfectly aligned so that it would pass through the atmosphere of each as it crossed the Solar system, it would come even close to slowing it down enough to keep it in the Solar system. As far as tight turns around the Sun goes: To deflect the probe by as little as 1 degree, would take the full surface gravity of the Sun acting on it for ~1.5 hrs. But the probe is not going to be in the vicinity of the Sun for any where near that long. In 1.5 hrs it will traveled more than the diameter of Mars' orbit. This means that even when just skimming the surface of the Sun, the probe will have its course changed hardly at all. The practical aspects of the problem don't even come into play, as the idea won't work even in theory.