Thread: How Fast is Fast?

If nothing can go faster than light then how about light itself.

http://www.scienceblog.com/cms/light...rds-10590.html

I can't figure out what you are driving at. The speed of light is the speed of light.

Originally Posted by mathman

I can't figure out what you are driving at. The speed of light is the speed of light.

I understand that. I'm more or less asking if the speed of light can be boosted in whatever medium it is traveling through.

It's an interesting article. Makes my head hurt

Originally Posted by zinjanthropos

Originally Posted by mathman

I can't figure out what you are driving at. The speed of light is the speed of light.

I understand that. I'm more or less asking if the speed of light can be boosted in whatever medium it is traveling through.

The speed of light in a vacuum is the maximum. In different mediums it will be slower.

Originally Posted by mathman

Originally Posted by zinjanthropos

Originally Posted by mathman

I can't figure out what you are driving at. The speed of light is the speed of light.

I understand that. I'm more or less asking if the speed of light can be boosted in whatever medium it is traveling through.

The speed of light in a vacuum is the maximum. In different mediums it will be slower.

While true, there is a subtle point that the article the OP links takes advantage of. Read the article. Basically they've managed to create a metamaterial which makes it appear that a light signal travels faster than c (though it doesn't break any laws... something about using the leading edge of the light's wavefront to reconstruct the full signal or something. Like I said, makes my head hurt).

This is a continuation of the "resonances" in beams of light we had some time back. Light does not travel faster than light but the PEAK in a beam appears to. It is an optical illusion.

Maybe somebody can answer this for me.

How fast can a neutron star spin? Has anybody ever figured that out?

Originally Posted by zinjanthropos

Maybe somebody can answer this for me.

How fast can a neutron star spin? Has anybody ever figured that out?

Pulsars are neutron stars. Their rotation frequency slows down slowly. The fastest rotation periods have been observed down into the millisecond range.

Originally Posted by Dishmaster

The fastest rotation periods have been observed down into the millisecond range.

Can that be converted to km/sec? An approximation or range will do.

Originally Posted by zinjanthropos

Originally Posted by Dishmaster

The fastest rotation periods have been observed down into the millisecond range.

Can that be converted to km/sec? An approximation or range will do.

Rotation isn't really measured in distance per time. A point on the surface of a pulsar at its equator would be moving at something like:

Speed (km/sec) = circumference (km) x rotations per second

Which for a normal 12km radius pulsar rotating at the higher end speed of around 600 rotations/sec would give you a surface velocity at the equator of about 45,000 km/sec. Very fast, but nowhere near the speed of light.

Super-massive black holes as in millions, even billions of solar masses (one sun's mass) have been found rotating at almost light speed.


This is about the fastest matter can travel (possibly from a hyper-nova):

Cosmic rays with even higher energies have since been observed. Among them was the Oh-My-God particle (a play on the nickname "God particle" for the Higgs boson) observed on the evening of 15 October 1991 over Dugway Proving Grounds, Utah. Its observation was a shock to astrophysicists, who estimated its energy to be approximately 3 × 10^20 electronvolts (50 joules)—in other words, a subatomic particle with macroscopic kinetic energy equal to that of a baseball (142 g or 5 ounces) traveling at 96 km/h (60 mph).

It was most probably a proton with a velocity only very slightly below the speed of light. To a static observer, such a proton, traveling at 1 − (5×10^−24) times c, would travel only 47 nanometers (5×10^−24 light-years) less than a light-year in one year.

http://en.wikipedia.org/wiki/Ultra-h...rgy_cosmic_ray


.

Originally Posted by Cyberia

Super-massive black holes as in millions, even billions of solar masses (one sun's mass) have been found rotating at almost light speed.

I read that black hole spin frequencies are actually measured at the event horizon. Does that mean the spin speed is actually calculated from the drag of spacetime at the EH?

We measure the speeds of material in the accretion disk, before it is pulled into the EH. The paths of such material would indicate "spacetime being dragged" by showing the paths taken by the material into the EH.

About a year ago, a several solar mass black hole was shown to have a safe orbital area just 100 miles from the surface of the EH where matter was not pulled in (which I find strange as it would be virtually in the centre of a star of several solar masses.)

Originally Posted by Cyberia

We measure the speeds of material in the accretion disk, before it is pulled into the EH. The paths of such material would indicate "spacetime being dragged" by showing the paths taken by the material into the EH.

About a year ago, a several solar mass black hole was shown to have a safe orbital area just 100 miles from the surface of the EH where matter was not pulled in (which I find strange as it would be virtually in the centre of a star of several solar masses.)

Staying on topic.....were they able to measure the orbital speed of any material in this area?