Mez

would the speed of sound be considered to be the universal speed limit? It's difficult to imagine, I know, however if we evolved without eyesight or the sense of touch (couldn't feel heat), wouldn't we be convinced that sound was the fastest speed possible, and that if we went faster than the speed of sound, we would travel through time? Extrapolating in the other direction, since we have evolved without sensors which can detect anything which travels faster than the speed of light, isn't that why we think that the speed of light is the universal speed limit? Just curious!

Maybe I have asked this before, however perhaps different people will read and answer it this time. We all know about the phenomenon of light shifting in frequency as the observer is either approaching or retreating from a source of light. That's called blue shift and red shift respectively. We also know that the energy of a photon is given by Plank's constant multiplied by the frequency (E = hv). So, if a photon is emitted from a light source and I measure it's energy in a stationary frame of reference, I will get a certain value. If I measure the same photon's energy in a moving frame of reference (approaching the source or retreating from the source), I will get a different value. The photon itself hasn't changed, so where did the extra energy come from, or where did the energy go?

We all know that E = hv, where h is the Plank constant and v is the frequency of the electromagnetic radiation. Now, let's consider the case where an object radiates say, 10 photons of yellow light, however the object is travelling away from the observer, so the light appears red-shifted (let's say it appears red) to the observer. So, the photons, when they were created, had an energy of say, 36 x 10^-20 joules each (yellow light), however when observed, have an energy of only 28 x 10^-20 joules (red light). Where has the energy gone? If energy is conserved, where did it go? If energy is not conserved, doesn't that violate the very basics of physics?

Within relativity theory, it is suggested, maybe even proven, that gravity bends space, such that the path of light is similarly bent around massive objects, while the light itself "thinks" it is travelling in a straight line. Could it be that the speed of light in a vacuum is actually impeded by a change in gravitational field? That the "aether" proposed back in the days of yore (and supposedly disproved by Michelson and Morley) is actually gravitational gradient? That the experiment carried out by M&M used a horizontally mounted apparatus, such that the beam of light remained within the same intensity of gravitational field the whole time. It just seems odd to me that the reason the speed of light in a vacuum is the universal speed limit is because we cannot create anything less than a vacuum. I mean, we can slow light down by passing it through a medium such as air, water, glass etc, however a vacuum represents the ultimate in "lack of matter", however even without matter in the vicinity, gravity is everywhere. It would be interesting to conduct M&M's experiment with apparatus mounted perpendicular to the horizontal plane to see if it revealed any different result. So, my question remains, could gravity (or more specifically delta gravity) be the aether which was postulated in the late 19th century? http://en.wikipedia.org/wiki/Luminiferous_aether

Will we be encouraged to increase greenhouse gas production so as to retain heat in the atmosphere to lessen the effect and / or likelihood of the next ice age? It seems ironic, but if there is a firm belief that humans contribute to / have such an impact on global warming, wouldn't we therefore have a good chance of preventing the next ice age from occurring?

This is an ion thruster / ion engine http://en.wikipedia.org/wiki/Ion_engines

What level of gas compression could be achievable? 2 Atm?

Just curious....

Going back to my previous "laser pointer on the turntable" problem. If the laser pointer is rotating fast enough, and the distance from the laser pointer to the wall is far enough, surely the spot where the laser hits the wall can appear to move faster than the speed of light? Of course I realise that the "spot on the wall" is not a material thing, however if we consider the scenario where the wall is replaced by a cylindrical mirror, then the reflected laser would appear to an observer located at the pointer, to be a source of light that is travelling faster than the speed of light, surely? If this is so, what would science do to prove that the light was not in fact travelling faster than the speed of light? Yes, I understand that the light itself is travelling radially out from the laser pointer to the wall/mirror and radially back again, but the spot on the wall/mirror is still moving at faster than the speed of light.

A cylindrical wall is established surrounding the apparatus.

a. How far from the laser pointer should the wall be, in order for the spot from the pointer to travel at the speed of light?

b. If the wall is dismantled and built again at twice the distance from the apparatus, how fast does the spot from the laser pointer travel?

c. In part b, above, if the cylindrical wall is made from a mirror and I sit at the position of the apparatus, do I see a light source that is traveling faster than the speed of light? If so, how can this be? If not, why not and what DO I see?

The entire experiment is set up in space so that there is no (or little) degradation of the laser light.

In bright sunlight, there is a lot of glare in my right eye. If I look down, I can see clearly through my right eye's peripheral vision. If I wear sunglasses, my vision is somewhat restored. It is as if there is an opaque mass in my vitreous humor. I don't believe it is a problem with the cornea or lens. Apart from seeing an opthalmologist (no pun intended!), can someone tell me whether there is a condition / disease where the vitreous humor becomes crystalised in spots?

Secondary question: Has anyone ever invented a "gravitational shield"? I am not talking about anti-matter, nor anti-gravity, nor levitation. It is possible to build a "Faraday cage" to exclude all electromagnetic fields, but I want to know whether it is possible to build the equivalent for gravitational fields. All opinions are welcome.

The scenario is a lighthouse at the North Pole, whose beam rotates at 1 revolution per second. Ignoring attenuation by the earth's atmosphere and the rotation of the earth, my original question was how far along the beam would it be travelling tangentially at the speed of light. The answer that were provided said that the "beam" is not solid and that in fact the photons in the beam are all travelling radially, with no tangential component. This I can accept. Now for my next installment:

Imagine that there is a mirror in the shape of an anulus (ring) at a distance "d" from the lighthouse:

1) What is the value of "d" (let's call it D) such that the intersection of the beam of light and the anulus moves at the speed of light (c)?

2) If the anulus was at a distance of 2D from the lighthouse, what will the speed of the intersection of the beam and the anulus be? Let's call it z.

3) What will I observe as I look towards the anulus from the lighthouse?(i.e. direction of reflected light

Everywhere I have been in the world, the entry door to a public toilet facility opens inwards, which means when I am finished and I wash and dry my hands, I need to grab a handle to get out! I don't know how many people have used the facility and NOT cleaned their hands before exiting! So, now my hands are dirty again. Surely outward opening doors which I could push with my forearm or shoulder would be better?

The scenario is a lighthouse at the North Pole, whose beam rotates at 1 revolution per second. Ignoring attenuation by the earth's atmosphere and the rotation of the earth, my original question was how far along the beam would it be travelling tangentially at the speed of light. The answer that were provided said that the "beam" is not solid and that in fact the photons in the beam are all travelling radially, with no tangential component. This I can accept. Now for my next installment:

Imagine that there is a mirror in the shape of an anulus (ring) at a distance "d" from the lighthouse:

1) What is the value of "d" (let's call it D) such that the intersection of the beam of light and the anulus moves at the speed of light (c)?

2) If the anulus was at a distance of 2D from the lighthouse, what will the speed of the intersection of the beam and the anulus be? Let's call it z.

3) What will I observe as I look towards the anulus from the lighthouse?(i.e. direction of reflected light

Ignoring attenuation by the Earth's atmosphere, how far out along the beam will the beam be travelling tangentially at the speed of light? Beyond this distance along the beam, will it be travelling tangentially faster than the speed of light? Remember, I am not refering to the speed radially, along the beam, but rather tangentially as it rotates. Also, please ignore the speed of rotation of the Earth, I am only interested in the rotation of the beam.

Why doesn't your head appear at the bottom and your feet at the top?

A slow bowler bowls the ball. The facing batsman hits the ball back towards the wicket at the non-striker's end on the full. The bowler dives across to catch the ball. Before the bowler clasps the ball, the force of the ball pushes the bowler's hand onto the wicket at the non-striker's end (the ball is in contact with the bowler's hand when this happens) and the wicket is broken. The non-striker is backing up, and is out of his crease at this time. The bowler does clasp and catch the ball on the full. So, who is out? Is the non-striker out "run out" or is the batsman out "caught". Of course there is no double-play in cricket. Once a wicket is taken, the ball is dead!