How do we measure faster than light speed ?

(Nov 19, 2016 01:08 AM)Syne Wrote:

(Nov 19, 2016 01:02 AM)RainbowUnicorn Wrote: what is light when it is not moving ?

Light can only exist moving.

why cant we gather existing light and store it without converting it ?

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(Nov 19, 2016 01:50 AM)Secular Sanity Wrote:

(Nov 19, 2016 01:02 AM)RainbowUnicorn Wrote: What is light when it is not moving ?

It can be stored for a short time in the excited states of atoms.

BTW, a photon doesn't experience time or distance.

Hey SS.
Thanks for joining in.
i was just reading some stuff on photons not expereincing Time or Distance.
and... how it speeds up to maintain its relative speed to distance(time) via gravity.
vaguely grasping that it changes colour/frequency ?(particle & wave etc)

 so in essence have we been able to establish if the photon in fact already exists at point x ?
or is this the observer effect that we must in turn create it to make it be in the closed box(point x{travelling to what we wish to make it bounce off}) ?

(Nov 19, 2016 02:10 AM)RainbowUnicorn Wrote: Hey SS.
Thanks for joining in.
i was just reading some stuff on photons not expereincing Time or Distance.
and... how it speeds up to maintain its relative speed to distance(time) via gravity.
vaguely grasping that it changes colour/frequency ?(particle & wave etc)

 so in essence have we been able to establish if the photon in fact already exists at point x ?
or is this the observer effect that we must in turn create it to make it be in the closed box(point x{travelling to what we wish to make it bounce off}) ?

It doesn’t seem like you understand enough to form a proper question.  Maybe you could start by asking just one question at a time.

(Nov 19, 2016 01:50 AM)Secular Sanity Wrote: It can be stored for a short time in the excited states of atoms.

That's not exactly true. The photon, itself, cannot be stopped or stored. It's energy can be passed on to atoms which can later emit that energy again as a photon. It cannot be said to be the same photon.

(Nov 19, 2016 05:11 AM)Syne Wrote: It cannot be said to be the same photon.

Did I say that it was?

Question: What is light when it is not moving?  

Answer:  It becomes stored energy, which is no longer light.

By using two light beams, they can induce an electromagnetic transparent medium, where both beams can propagate with almost no absorption.

If they turn down the laser that made the medium transparent, they can reduce the polaritons made of photons, and then they can increase the polaritions made of atoms.  The light is then effectively stored in the medium.  The photons become dark-state polaritons, which are excitations in the medium.  In other words, the medium becomes briefly opaque.  When they turn the laser back up, the polaritions are converted back into photons.

Everything is stationary in its own frame of reference, but of course Syne already knows this because he is so smart and yet so gracious.  

(Nov 19, 2016 02:39 AM)Secular Sanity Wrote: It doesn’t seem like you understand enough to form a proper question.  Maybe you could start by asking just one question at a time.

ok thanks, yes you are correct. most soo in defining the nature of what i am pondering as the question.
i shall give you my basic questional premise which i was attempting to work forward to however i seem to have got lost off the starting blocks.

how do we know that we cant travel faster than light ?
if light can be effected by gravity then why cant we measure lights as a mass ? (or can we)

hope that makes more sense

(Nov 19, 2016 06:06 PM)RainbowUnicorn Wrote: how do we know that we cant travel faster than light ?

I've never found FTL interesting, but you can read up, if you'd like.

http://math.ucr.edu/home/baez/physics/Re...t/FTL.html

RainbowUnicorn Wrote:if light can be effected by gravity then why cant we measure lights as a mass ? (or can we)

Gravity is space-time curvature. Light follows a straight path but the path is curved by mass.

thanks for the link, ive saved it for reading

i have pondered if FLT is inherantly flawed the same as faster than sound travel thinking. simply by lack of ability to quantify & understand.
though... given quantum duality maybe speed in its self is irrelivant and only relivant to the observer of the event rather than as you say the photon expereinces no time.


Secular Sanity
"Gravity is space-time curvature.  Light follows a straight path but the path is curved by mass."

ok i need to unpack that into my brain.

the path is not curved to the photon though because it simply accelerates to be in the same place in the same time yes ?
so Gravity is not bending light but bending space/time & the photon simply continues being a photon(potentially devoid of Gravity an effecting causality?

(Nov 19, 2016 06:51 PM)DRainbowUnicorn Wrote: the path is not curved to the photon though because it simply accelerates to be in the same place in the same time yes ?

No. It's gravitational time dilation.

https://en.m.wikipedia.org/wiki/Gravitat...e_dilation

(Nov 19, 2016 04:21 PM)Secular Sanity Wrote:

(Nov 19, 2016 05:11 AM)Syne Wrote:

Secular Sanity Wrote:

Quote:What is light when it is not moving ?

It can be stored for a short time in the excited states of atoms.

That's not exactly true. The photon, itself, cannot be stopped or stored. It's energy can be passed on to atoms which can later emit that energy again as a photon. It cannot be said to be the same photon.

Did I say that it was?

Question: What is light when it is not moving?  

Answer:  It becomes stored energy, which is no longer light.

By using two light beams, they can induce an electromagnetic transparent medium, where both beams can propagate with almost no absorption.

If they turn down the laser that made the medium transparent, they can reduce the polaritons made of photons, and then they can increase the polaritions made of atoms.  The light is then effectively stored in the medium.  The photons become dark-state polaritons, which are excitations in the medium.  In other words, the medium becomes briefly opaque.  When they turn the laser back up, the polaritions are converted back into photons.

Jeez, are you really so insecure that you can't even stand to have your answer clarified to possibly help someone else understand? Your original answer was not "It becomes stored energy, which is no longer light." You said, "It [light] can be stored for a short time in the excited states of atoms." It should be obvious that the OP could easily misunderstand that answer. But no, your fragile ego must take priority, even in a thread asking physics questions. It's truly pathological.

And yes, I was referring to electromagnetically induced transparency as well, where the data of an image can be retrieved from atomic spin excitations within about a minute. Not only is the energy of the light stored, but the pattern of the light can be retrieved.

Quote:Everything is stationary in its own frame of reference, but of course Syne already knows this because he is so smart and yet so gracious.

No deary, a photon has no proper frame of reference. You'd think you'd know that, since you even said "a photon doesn't experience time or distance." A frame of reference is a co-moving coordinate system. No coordinate system can be "experienced" without time and distance.

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(Nov 19, 2016 02:10 AM)RainbowUnicorn Wrote:

(Nov 19, 2016 01:08 AM)Syne Wrote:

(Nov 19, 2016 01:02 AM)RainbowUnicorn Wrote: what is light when it is not moving ?

Light can only exist moving.

why cant we gather existing light and store it without converting it ?

Massless particles, like photons, can only be said to exist when their momentum lends them relativistic mass. If you could stop them, they would lose all the properties that allow us to observe them. And since the first law of thermodynamics (conservation of energy) says we cannot remove momentum without that energy being converted to something else, even though the photon disappears, its energy must be absorbed elsewhere.

http://www.askamathematician.com/2013/04...it-travel/