Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum light speed

I am sorry I was off-line yesterday. Both observers observe from their respective reference frames within which each one is of the opinion that he is stationary. If both switches on a flashlight along the direction in which they are moving, the trailing observer will not see any light coming from the leading observer. The leading observer will see the light from the trailing observer approaching him with a speed c; however, it will be redshifted (Doppler shift) because the leading observer will see the slower moving trailing observer moving away from the leading observer. If the leading observer points his flashlight backwards towards the trailing observer, then the trailing observer will also see this light travelling towards him with the speed c. It will also be redshifted because the trailing observer will see the leading observer moving away from the trailing observer. I hope this is of help?

Okay I get what you're saying now...BUT who, and how, did someone come to the conclusion that the leading observer would see a redshift as opposed to a light approaching slowly?

that came from an understanding of wave principles.

its the same for train whistles.

if you stand near a train crossing, as the train approaches, the whistle goes higher "redshifting" in to higher frequencies. this is because sound cant change its speed for a given temp and pressure. therefore the waves are closer together, increasing the frequency of the sound. after the train passes, the waves are farther apart causing the sound to drop (the same as blue-shifting for light). doppler radar does the same thing with radar to give a better understanding of clouds.

astronomers have seen that galaxies that are moving away from us have a distinctive redshift and those (few i believe) moving towards us, are blueshifted.

with the observer, the light cant move at any different speed that it does, therefore the light will be redshifted as he moves forward.

Origionally posted by Empire:
"Anyway I'm trying to understand more about this topic now. I know light, even from a stationary object, can go faster than the measurment of the speed in a vaccum. "Scientists have seen a pulse of light emerge from a cloud of gas before it even entered."


You should understand that the effect referred to is
a result of a change of the shape of a pulse of light.
The pulse itself, as a whole, does not violate 'C`.

While something might come of the study of this effect in the future,
right now it is just a curiosity.

It seems that i just cannot get to my computwer in time. this time i fell ill and had to spend two days in hospital. Thank God for antibiotics!

Accordng to the trailing observer (who is under the impression that he is stationary) the leading observer is moving away from him. Vice versa, according to the leading observer (who is under the impression that HE is stationary) the trailing observer is moving away from him in the opposite direction. Both observers measure the SAME light speed and the same speed v with which each is moving away from the other. Therefore both observe a redshift in the light emanating from the other observer.

I am sorry I used the qoute command instead of the edit command. I am still a bit weak from the fever I have had.

ok check this equation out al=006843/,00912<1>=fa,zx-474758809-0909707[08

Hmm, this is a good one. This question appears also in the Cornell U physics class.I will give you the standard, mainstream answer from same webpage.They have a whole bunch of cool problems on that website. Here goes the answer:

If we admitted by ABSURD that the rocket COULD be accelerated to run at .99999c speed (it cannot, no massive particle can run at c) , the light from the headlights would STILL run at c in front of the rocket and wrt the rocket! So, we would see the light cone of the headlights.
I know that you may have received a lot of other answers but this is what SR predics. Unfortunately, we cannot put it to test

Sugeo: Time does not pass for a photon. It would be reasonable to assume that the theoretical rocket traveling at c would similarly not experience time.

I'm not sure your assumption holds.

Though neither does the entire analog as it is, it appears, impossible to test.

This is why I used all the disclaimers (.999999...9c, ABSURD, etc)

I cannot understand why men are always attaching limits to things that do not belong to them.

the speed of light is whatever speed you can get light to travel at...

my point here is as follows...

laser beams are in common use today.

a laser beam only works because (((( LIGHT ))))
photons are reflected off of mirrors several thousands/millions/who knows of times until its ((( SPEED ))) is great enought to pass through a
partialy silvered mirror at one end.

the initial light (is light) and its initial speed is (the speed of light) isnt it?

then what purpose does the reflecting off the mirrors serve?

I don't know. What is the purpose served by making statements are are nonsensical and then asking questions easily answered by going to google or wikipedia?

I read the explanation in 1963. It hasn't changed since then.

But the willingness of people to be lazy seemingly has.

you obviously have no idea what how a laser works. as someone that spent years learning it, ill explain.

one of the mirrors (on most mirrors) is a straight full reflecting surface. the other is a partial reflective surface. youve all seen mirrors like this. when you drive, the mirror inside the car has two settings. during the day, you have it set one way and can see clearly behind you via the mirror. at night, when a car is behind you, you turn it to the second setting and the light does not seem so bright. a person setting in the car with you, will see the light hitting your cheek or your forehead. the reason is that the mirror has two surfaces. the front is a partial reflective surface, reflecting about 10 percent of the light. the second surface (the back one) is fully reflective. the two surfaces are set a short angle apart. that allows you to see the two images at a different spot.

in a laser the second mirror (low reflective) reflects a part of the laser back, and allows the rest to pass. depending on the size and type of laser it could be anything from a 1 percent to a 99 percent reflective. there are even a few that dont have a second mirror. a small number of them actually dont have mirrors. they have an exciter laser, usually something like a led laser, that is beamed though a medium, taking the energy from the molecules as it passes.

the mirrors and medium does not increase the speed of the laser. if it did, there would be too many varibles for the laser to work.

The point of the mirroring, which often happens by total-internal-reflection (TIR) is that photons Stimulate the Emission of Radiation ... thus SER in laSER. If the photons do not make multiple passes there is less likelyhood that they will collide with an excited atom and stimulate further emission.

This is not significantly different than the reason why neutron reflection is used in nuclear weapons.

OK..So what I should have said is that the light ENERGY emmited increased instead of the speed of light increasing.

so if I excite atoms with light ( photons ) and make them emit radiation inside a medium
(such as a ruby for instance)
and I contain some of the light ( photons ) inside the (ruby) by placing mirrors on each end of the ruby , one fully mirrored and one partially mirrored the photons will bounce back and forth between the mirrowed surfaces exciting more and more atoms until the partially mirrored surface can no longer contain the photons and they escape , or is it the energy that escapes.

if I can use a 12 volt battery at 100 amps and produce a light source greater than that which could be produced by the battery itself without the laser then has ENERGY increased?

So tell me what actually increases?

I know the intensity of the initial light source does not change.

I know the intensity of the light emmited from the laser is greater than the initial intensity of the light source.

if the laser uses 1 unit of ENERGY in 1 unit of time , and the laser outputs 2 units of ENERGY in 1 unit of time then what has happened?

No Paul you can not get something for nothing. You can take the energy in your battery and produce coherent light from it. But you will, at best, get a few percent efficiency with your ruby. It is the coherency that counts.

Here's a hopefully useful analogy. Stand out in the sun on a hot day and look at the top of your hand. Nothing is burning. Focus that light through a lens (losing 5-10% of the energy) onto your hand and you will be in a world of pain.

Nothing increases. What you are getting is focus.

The intensity is not greater from the laser. The energy is not greater. Coherent light is essentially giving you a greater impact with a lesser force.

HTH

the only way you can have "tir" is if you use cavity dump pulse lasers. these have 2 high reflecting mirrors (hrm) but will open for a single pass of the light so that all of the energy in the cavity will dump out in a single pulse. in a normal laser one is a hrm and other a lrm (low reflective mirror). it only reflects a percentage of the energy, anywhere from 1 percent to 99 percent, perhaps even with a few points past the decimal. It all depends on what kind of medium and how big it is.

one of the ones that does not use mirrors at all is what is commonly called a jet laser. it uses a fuel that after combustion has high energy co2 and no2 as its exhaust. the exhaust is then fed into a chamber that causes it to travel a wide but low path, where a initiator beam is fired into it, to cause the stimulation. some forms of this will have the beam chamber a little higher and cause the beam to travel though it on parallel course two to four times. the trick is that no part of the exhaust has the beam travel though it more than once. this is suppose to create a extremely powerful beam. it was hoped at one point that it could be used as an antimissile or aircraft gun. while it worked on drones, it never was very effective on faster, bigger targets like aircraft, and even less on smaller, even faster targets like missiles.

one of the biggest laser in the world was called antares which was suppose to be used to create a hydrogen fusion to powered an electric power plant. scientifically it was a smashing success as it manage to cause fusion in more materials that hydrogen. it total took them off guard when it caused aluminum fusion.

financially, it was a huge bust. it did create more electricity than it used, enough to provide energy for a very small town. the cost to do so would have provided electricity for a medium size city using more conventional means. most dye lasers use a laser initiator too, using mirrors to change the path, rather than bounce it back and forth.

its not so much the intensity that changes as the fact that all the energy is in the same wavelenght and in the same phase.

light is a sinewave. in normal light the light will have many different wave forms, each giveing you a different frequency of light (it appears different colors). most laser has only one frequency, and the all the energy will be in the same part of that wavelength. there are some lasers, mostly weaker ones, such as helium neon lasers (hene)that lase (release light) in multiple frequencies. others such as argon can do so, but due to the fact that choising a single wavelenght gives considerable more power, they use a prism near the high reflective mirror to tune it to which ever frequency they choise. others use two lrms inside the cavity to cause the meduim to only release in the one frequency they choice.

the energy that you put in will give you the same energy out no matter how you do it, just some things can cause it to be more usefull than others. da analagy to the lens and the sun is a good one.

dehammer wrote:
"the only way you can have "tir" is if you use cavity dump pulse lasers."

Every ... and I mean every ... Gallium Arsenide and Gallium Arsenide Phosphide laser uses TIR ... not mirroring.

But thank you for your contribution.

i went to college in the 1980's. at that time there were no such thing as total reflective mirrors on both sides of all laser cavities. one side it has total reflective (or to be more precised high reflecive since even aluminum mirrors allows some forms of radiation to pass) and on the other it has a mirror that allows some of the light to pass through. when you built the lasers in the 1960's how many years did you study lasers.

did you know that they have even taught chimps to assemble things now. if a few decades they may have them trained to assemble lasers. that will not mean they will understand them, just that they can build them if they are given all the parts. to understand lasers you need to actually study them, as in go to school to see how they work, operate, and what different kinds of lasers that exist. I did. Did you? your answer says not. there exist lasers with no mirrors at all.

if they dont have mirrors how do they reflect the light. light is reflected by mirrors. most of them use metal mirrors but they still use mirrors and some of them use plain old glass mirrors. grantted these are not the type that you go to walmart to buy, but they are still mirrors and they are not total reflective on both sides of the cavity (except for cavity dump lasers as i pointed out earlier).

you may be able to talk rings around me with talk about oracle programs, but when it comes to lasers, i know what i'm talking about.

if you would like to know more about lasers here is a site that gives an explination that even a junor high school student should be able to follow. anyone that has kids that wants to know about lasers, heres is the place to send them.

http://www.howstuffworks.com/laser.htm

da, i see part of the problem. you were talking about solid state lasers which are basically what you described, while most lasers are not. the most common lasers are gas lasers. although with the popularity of key light lasers (laser pointers used for key holders to show your keyhole) the solid state ones are getting more common. the thing is that even the solid state have a kind of mirror on both ends.