Physically speaking, sound is transported by the collisions of molecules. The easier it is for molecules/atoms, to collide (higher density of the medium) the faster sound travels. Above 100 km altitude, the average distance between air molecules is so high, that these molecules don't collide on a regular base and spend most of the time flying in their own orbits, just like very small satellites. No collisions, no transport of sound.
Just as the velocity of sound depends on the density of the medium through wch it is being propogsted, the velocity of light also varies depending on the medium through wch it is propogating.
Thus the speed of light is not constant ,but changes according to the density of the medium (and temperature) it is traveling through.
Light has a constant speed of 3 x 10^5 km/second = 299,792,458 meters/second = (186,282 miles/second) =(9.5 trillion kilometers /year) through the medium of a vacuum or empty space(according to quantum physics even a perfect vacuum is not empty,but teeming with virtual particles that are popping in and out of existance over very short time frames.This suggests that so-called "empty space" is actually permeated with unobservable energy and invisible forces that are inaccessible to our senses.The energy density of empty space is immense and might account for the missing "dark energy" that is unobservable.If we could tap into this hidden store of energy we would have an unlimited source of fuel/energy.However no one has yet come up with an experimental method to weigh a cubic meter or more of "empty" space in order to measure the weight/mass-equivalence of the virtual particles contained therein).
How can massless energy(photon) materialize into a particle with mass and inertia?
If the speed of light diminishes with increasing density of the medium through wch it travels, at what density of matter would the velocity of light become zero?).
Perhaps the reason light cannot emerge from a Black Hole has something to do with the very high density of it's content/composition?
Light slows to about 225,000 km (140,000 miles) per second when it goes through water( speed of light in ice is 2.29x10^8 m/s) ,and about 206,000 km (128,000 miles) per second when it goes through quartz crystal and 124,000 miles per second through glass. A diamond, , will slow light to 125,000 km (78,000 miles) per second--this is less than half the speed through vacuum!).
Composite white light separates into its constituent frequencies upon passage through a transparent prism because each frequency is slowed down to a different degree according to its energy content.
But photons don't really slow down.rather each hits an atom,gets absorbed and another gets emitted. This process takes different amounts of time depending on the medium and the energy content (frequency) of the photon,hence the time delay.The photon that strikes the window is not the one that emerges on the other side.Is this a complete explanation of the mechanism by wch light slows down when it enters a denser medium?
Light moving through a Bose-Einstein Condensate ( a state of very condensed matter found at near absolute zero)travels at very slow speed. What determines this difference between how much light is slowed?Lene Hau was able to slow light to 17 metres per second by passing it through a transparent superfluid --Bose-Einstein Condensate--a state of matter that only exists at near absolute zero temperatures.Dr. Hau and her associates at Harvard University have successfully transformed light into matter and back into light (was able to momentarily stop/capture a beam of light)using Bose–Einstein condensates. Details of the experiment are discussed in the February 8, 2007 publication of the journal Nature (see entry in this journal titled "Light and Matter United")
Since most of space is within a few degrees of absolute zero (the temperature at wch Bose-Einstein Condensates occur)it is not outside the realm of possibility that light has traversed such a state of matter in reaching us .Such an occurrence would necessarily have slowed it's speed unpredictably and makes "distance to origin" calculations of questionable acracy!This means that light passing through a cloud of dust,gas , plasma,or a Bose-Einstein Condensate (i.e.,non-empty space) would have it's path refracted and/or slowed thereby giving an observor a false position for the emitting object.
Can we ever accurately know the exact (versus apparent ) position of light-emitting objects in the night sky?
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Perhaps the "medium" through wch electromagnetic waves propogate is the omnipresent Higgs Field?
ReplyDeleteIt is accepted dogma that
Deleteunlike water and sound waves, light does not need a substance through which to travel. Instead, it consists of waves of alternating electric and magnetic fields that move through a vacuum at the cosmic speed limit of 186,000 miles (300,000 kilometers) per second.
But I have yet to come across a credible mechanism for how electromagnetic "waves"
propogate through empty space.
ss
We accept that photons move through empty space ,...but how?
DeleteHow do tbey move at 300,000 km/s
without losing energy?
If light is both particle and wave, and particles unlike waves can travel through empty space
Deletethen light as particle can propogate through vacuum (
What is the minimum mass of a neutron star wch has sufficient gravity to prevent it from radiating light?
ReplyDeleteWould such an object be a "black neutron star" or would it have become a Black Hole?
Wouldn't the speed of sound also be reduced at very cold temperatures because the vibration/motion of the atoms of the medium approaches zero?
ReplyDeleteWhat is the mechanism by wch light gets "amplified" or multiplied upon passage through some medium such as a ruby?
ReplyDeleteYou can slow light to zero velocity by shining it at an opaque surface.
ReplyDeleteThe light is absorbed and its energy is transduced and dissipated as heat!
So what's the big deal!
http://www.mifp.eu/OECS13/
DeleteSo you are saying that light originating at the Big Bang event
ReplyDelete(for instance)
if it traveled through a Bose-Einstein Condensate to reach us
would have been slowed to such an extent that
all our calculations of distance to origin would be corrupted and inaccurate.
What we need is a means of speeding up light (not slowing it down).
ReplyDeleteRight now the (slow) speed of light is a formidable barrier to exploring the universe!
We need to find a way to transcend that limitation!
There are billions of earth-like, habitable life-sustaining planets in our galaxy alone waiting to be physically explored (there are 100 billion solar/planetary systems in our galaxy, and each has at least one planet in the "habitable" zone.
DeleteBUT it would take 4.3 years traveling at light speed (at 300,000 km/s)to reach our nearest neighbor sun. At the speed of a Saturn rocket it would take 70,000 years!
Earthlings do not yet have the technological capacity to master intersteller travel.
http://earthsky.org/space/alpha-centauri-travel-time
It seems reasonable to think that
Deleteintelligent life forms that have had a much longer
time to evolve (compared to humans on planet earth)
elsewhere have developed the capacity
for intersteller and even intergalactic travel.
Is there a transparent medium/matter that reduces the speed of light more than carbon/diamond?
ReplyDeleteWhat is yhe speed of light through ruby?
I mean at normal temperatures--not at absolute zero like the Bose-Einstein Condensate requires?
The mineral "rutile" has a higher refractive index than diamond and would therefore slow the speed of light
Deletemore than diamond.
Hau used super-cooled sodium as the "medium" and managed to reduce the speed of light to zero. ...however, by the time it had slowed to a halt, all of the photons had been absorbed.
DeleteThe pulse of light could be regenerated because the photons' energy was stored in the atoms.
But while the pulse was stationary, technically, it contained no light at all.
What property of these materials causes light to transmit through them at different speeds?
DeleteWhat is the mechanism whereby rutile slows light speed more than diamond?
How is it related yo "refractive index"?
Perhaps like "superconductance" wch was first observed to occur only at very low tempuratures, this phemomemon of slowing light to zero velocity will one day be demonstrableat ordinary temperatures.
ReplyDelete(superconductivity is the total absence of resistance to the flow of electric current. Discovered in 1911, it was long thought to occur only in metals and only below a critical temperature (Tc) not far above absolute zero.)
The speed of sound and light respond oppositely to the density of the medium :
ReplyDeleteThe denser the medium the faster sound travels (water>ice>air)
The denser the medium the slower light travels.(air>ice>water)
How is density of a material related to its refractive index
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ReplyDeleteThe speed of sound is 4X faster in water than in air.
ReplyDeleteThe speed of sound at sea level — assuming an air temperature of 59 degrees Fahrenheit (15 degrees Celsius) — is 761.2 mph (1,225 km/h).
Because gas molecules move more slowly at colder temperatures, that slows the speed of sound; sound moves faster through warmer air.
The speed of sound in ice is nearly 3 times faster than in water.
In Ice, the molecules are trapped in a specific arrangement, making them VERY elastic (they will interact with a neighbor and snap back into place very quickly after they have been nudged by a sound wave), and speeding up the sound wave (this is why sound is faster in solids).In water, the molecules aren't as elastic, and they are MORE dense. This means that more interactions between neighboring molecules are required for the sound wave to propagate a given distance (making it slower).