swansont

That's the process to create a Bose-Einstein Condensate right? Followed by evaporative cooling.

Yes, although laser cooling can do lots of other things - lots of investigations into gases where the atoms move slowly. Cold collisions, atomic clocks, trapping radioactives for nuclear investigations, atom optics (atoms moving slowly have an appreciable deBroglie wavelength)

Here is a list of labs around the world that do atom traps. Fairly complete for research labs, I expect, but there are undoubtedly a few omissions.

This is a fun java applet that demonstrates evaporative cooling.

And is there no one to oppose the path of light? How about those cosmic particles in space? I mean after millions of light years even in space due to the opposition of those cosmic particles, light would slow down atleast a little, wouldn't it?

If light enters a medium with index >1 it slows down, and if it hits something it scatters. But within a medium of constant index, the speed is a constant. Space is a vacuum of moderate quality, so photons can make it quite far without hitting anything.

There is nothing like friction to act on light.

Ok, are plasma useful anywhere. And how does it behave differently from a gas? Because it basically is gaseous right?

One difference is that it contains ions, so they have interactions via the electric field rather than through collisions as with a gas.

There is more here with more links included.

Oh ok' date=' polarization is wave property, got it.

(I guess "wavicle" is a radical new way of thinking)

So, nature of light still remains mysteriously to us?

But assume that we know the nature of light, then what will we benefit from it?[/quote']

 

The nature of light becomes less mysterious if you study QM, optics and atomic physics for a number of years.

 

The benfits we have today are numerous. The benefits of tomorrow probably haven't been discovered (or at least exploited) yet. "It's really hard to predict what will or won't be invented in the future," he said, as he boarded the maglev train to take him through the undersea tunnel to the city of New Atlantis on the ocean floor.

Now that's a good thought. It sounds serious' date=' but after a second look it sounds funny too.

I guess it should "spin" fast enough to keep the people from drifting away.

7919.59594928933 m/s should be the approximate velocity it should travel to give earth like gravity(assuming that it's inner radius is the same as that of the earth, and using a=(v^2)/r). Does Earth spin that fast?[/quote']

 

If the earth spun so fast as to make the centripetal acceleration equal to g, we'd feel weightless (think astronauts in orbit) - so the answer has to be no. The earth spins at about v=40,000 km/86400 sec = 463 m/s at the equator.

But wouldn't Centripetal Acceleration give us gravity on the inside part of the ring? Assuming it is rotating along it's principal axis, ie perpendicular to the plane through the centre

Technically, no. But it would give an acceleration indistiguishable from gravity. You'd have "I can't believe it's not gravity!"

Just thinking would light have momentum' date=' should do cause of that guys experiment with the moving thing in the vacuum. then p=mv

pt=pi+pf =(m.c)+(m.c)......does this mean that light has different mass's? for different energies?[/quote']

 

The momentum of a photon is E/c. Which means you can scatter photons off of atoms and change their momentum, which is the basis for laser cooling and trapping (Nobel prize in 1997 for Chu, Phillips and Cohen-Tannoudji)

Certainly a Halo would have a gravitational pull' date=' assuming of course it has mass which the thing you're talking about invariably would.

 

How close it was to Earth's gravitational pull would depend on the ring's dimensions and density.

 

I'm not sure how to work it out exactly but it would probably have to be one fat (or deep) ring.[/quote']

 

There would be no gravity on the inside of the ring. Assuming a uniform mass distribution, gravity depends on the mass inside of your radius. This is from Gauss's law (used also in electrostatics - if the ring were charged there would be no electric field inside, either)

 

Whatever pull there is from the mass below your feet, it is counterbalanced by all the mass elsewhere in the ring. The sideways pull cancels from symmetry, but the up/down cancels, too. Even though a lot of the ring is far away, there's a lot of it compared to what's below you.

Ok got your first part' date=' But I lost track here

 

"It can't be a static device that can be used to e.g. shield half of a ferris wheel, because that's perpetual motion, too."

 

Could you elaborate.[/quote']

 

Put your static device, i.e. a "gravity shield," under one side of a large wheel, oriented like a ferris wheel. The unshielded side is now heavier than the unshielded side, so there is a perpetual torque on the wheel. Hook it up to a generator and you have free energy, violating the laws of thermodynamics. So we have reasonable confidence such a material/device doesn't exist, unless the shield uses more energy than the wheel can generate.

unless of course the theories are wrong causing the quantum mechanics to appear not to make sense. My quantum mechanics make sense' date=' but I do not agree with everything that I read.

 

Pincho.[/quote']

 

Relativity and QM have a few years of history of actually working.

 

What is "your" QM?

I know what the experiment was; I'm asking how the results show that "sci fi" time travel is not possible.

 

(Bearing in mind that relativity does not apply to all forms of sci fi time travel).

I didn't mean to imply that the experiment precluded sci-fi time travel. I was just clarifying that clocks ticking at different rates in the experiment was not an example of sci-fi time travel. Nothing in the experiment travelled backward in time.

Put another way, sci-fi time travel always boils down to how do you get around the causality problem. There was nothing acausal in the H-K experiment.

Ok' date=' can anyone listen to this hypothesis.

Light travels from a place to another in a straight line. For moving from one place to another it would need energy. But then, if it uses its energy(ie KE) then wouldn't it's speed actually [i']decrease[/i]? Then, velocity of light would no longer remain constant, right? But if velocity of light isn't constant(in a given medium), then what will happen to quantum mechanics?

An object moving has energy, but isn't necessarily using energy.

I was taught that light travelled in electromagnetic waves' date=' and hence it could travel in vacuum. Not because that photons were the medium.

And one small doubt. How does light "know" when to behave like a particle(Photo Electric Emission, Polarization) and when to behave like a wave(Simultaneous reflection/refraction, Interference of Light etc)? This question has been puzzling me for a long time.[/quote']

 

Light IS an electromagnetic wave. It's an oscillating electric and magnetic field.

 

One hurdle in this understanding is that we think of particles and waves as separate entities. So perhaps it would be easier to think of a light as a "wavicle," which has both particle and wave properties. We just can't do an experiment that measures both properties at the same time.

 

(Also - polarization would be a wave property - it's the orientation of the electric field oscillation.)

What is plasma? Isn't it a form after gas, or is it between liquid and gas? I thought it was after gas, but after reading yt's post, I'm now confused.

A plasma is basically a gas of charged particles. Once the temperature is high enough, there is enough thermal energy to ionize atoms and keep them from recombining. The behavior of such a collection of particles would be distinct from the other more common phases of matter.

plasma to gas would probably be De-Ionisation

Or recombination.

Violate which law of thermodynamics?

Any of them. If you can switch off an antigravity device, it is conceivable you could make a perpetual motion machine:

Turn the machine on.

Raise a mass.

Turn the machine off.

Let the mass fall and do work (e.g. turn a turbine)

If it took less energy to raise the mass than the work you extracted, you have perpetual motion. So if such a device exists, it must consume at least as much energy as you save in lifting the mass. It can't be a static device that can be used to e.g. shield half of a ferris wheel, because that's perpetual motion, too.

Once you start being able to create energy you coud also decrease entropy, so it really doesn't matter which laws of thermo you discuss; you'd be violating them.

Hey, this is confusing. So does that mean that If I travel at +0.6C and someone else travels at-0.6C (sign conventions), then we both will see light at C. Now if there's a stationary observer, won't he see light at 1+0.6=1.6C ??? And will mine and the other fellow's relative velocity be 0.6C+0.6C=1.2C. Or is there another formula at high speeds like swanson said.

The observers would see light at c, but of different frequencies. They would never measure another observer's speed as exceeding c; once you start moving fast you find that speeds don't add linearly (we just don't see it at small speeds). Your two observers would see each other moving at about 0.88c. See here

bump

 

the doppler effect...

 

if the doppler effect applies to light' date=' that would mean that when you move toward a source the light would get bluer, so would that speed up the waves relative to you, making them hit you at faster than C?

 

i dont get how no matter your speed a light beam will always travel toward you at C, and away from you at C if you are chasing it.....[/quote']

 

The Doppler effect changes both the frequency and the wavelength, such that the propagation speed remains c.

 

Everybody wants this (and quantum mechanics) to "make sense." Sorry. nature behaves differently at small scales and high speeds. Leave your "every-day behavior" expectations at the door.

here`s a question asked by my wife' date=' to which I have no answer.

 

on the Moon Landing pictures and other manned pictures of space, there never seems to be any stars when looking at the black void of space, and yet here on a clear night we can see them? the Hubble provides pictures of mega distant galaxies, land based telescopes of many distant stars, and yet all manned space footage that we`ve seen seems to be without stars?

is there any reason for this?

 

Cheers [/quote']

 

On a clear night we can see stars. That's certainly true. But were the moon pictures taken at night? No. They were taken during the day. Since the pictures are not overexposed, the camera exposure must have been set to account for the amount of light available. If you took e.g. a 1/100 sec exposure at night, would you see stars? Probably not. The stars are just too faint to show up in the pictures.

 

Also, there is "earthlight" present in addition to the sunlight, which is much brighter than moonlight is on earth. First of all, the earth is bigger, so there's more area for the light reflection. Second, the earths albedo (reflectivity) is higher by about a factor of 3, so there is more light reflected per unit area.

Most, if not all, of the standard moon hoax objections are addressed here

For what it's worth, Virtualbookworm.com is a print-on-demand publisher. It does both fiction and non-fiction; one of my friends published her novel through them. The author pays to have the book published (which is how the publisher makes money, not by actually selling books). I strongly doubt that the publisher was able to provide any sort of scientific peer review for this book.

Which is why saying that "X has written N books on the topic of Y" gives a false sense of authority and expertise about X. Anybody, in principle, can write a book.

For example' date=' Newton’s law of gravity can only perfectly explain why tides occur on the side nearest to it, but not on the other side.

[/quote']

 

The fact that many people do not understand the source of tides does not mean that that they are not explained by Newtonian physics.

The H-K experiment? Planes with a cesium clocks travelled westward and eastward for a number of hours, and a clock stayed on the ground. From the point of view of an inertial observer (not on the earth), the plane that moved west was travelling the slowest, and its clock sped up relative to the ground-based clock. The eastbound clock was going fastest, and it slowed down relative to the ground-based clock.

There was also a change in the gravitational redshift, because the planes flew at some altitude, and clock rates depend on your gravitational potential too. The overall effect was consistent with the predictions made by relativity.

yeah. it releases three types of stuff that sucks if you get hit. Alpha particles, which are just fast moving heliums, beta particles are fast moving electrons, and gamma rays...im not sure. But notice that speed is a key element here. and did i say that it sucks to get hit?

Gammas are photons released in nuclear reactions.

The bulk of the energy released in fission is in the kinetic energy of the fission products. Some energy will be released later on in the decay of the fisiion products, which tend to be beta decays. A small fraction of the energy released is in the gammas and neutrons. There really aren't an appreciable number of alpha particles involved in the reactions.

In a weightless enviroment the acceleration induced would glue the clothes to the drum. Because of gravity it falls at dryer speed across the center which is most efficient for drying. The only way to have the clothes stay in the center would be to have no gravity and no acceleration.

Just aman

For a dryer. But the discussion is about washing machines, so the spin axis is perpendicular to the surface of the earth. Gravity is irrelevant to the discussion.