Tagged Questions
2
votes
1answer
30 views
Relation of color and frequency for the visible spectrum
In this question the OP is looking for a way to see light that is outside of the visible spectrum without using electronic sensors. This got me wondering about the visible spectrum itself. Typically ...
1
vote
1answer
115 views
Why does Lorentz factor not hold for relativistic mass when we apply it to photons? [duplicate]
We know that the photon itself is massless particle $m_0=0$. But we also know, that the mass of the objects does increase with their energy. And we know that under certain circumstances (gravity, ...
1
vote
1answer
82 views
Could the shadow move with faster-than-light speed? [duplicate]
If I make a huge laser with a figure for shadow in front of the laser, and I shine it on to the moon, will I see the light from the laser AND the shadow moving the same speed? (I read somewhere the ...
1
vote
2answers
61 views
Speed and transparency of light
I have been puzzled with a fact that as an object moves faster, it ceases its property of opacity. I mean to say that as an object moves faster we can see right through it (more clearly than in a ...
-1
votes
1answer
61 views
How do we know that light is massless? [duplicate]
Almost everybody knows that light is massless. But where this come from and how it can be proven (experimentally or theoretically)? I actually found this article which explains and calculates the mass ...
4
votes
2answers
161 views
Can a dot of light travel faster than the speed of light? [duplicate]
Say I have a laser. If I spin the laser so that the beam sweeps in an arc along a very distant object, could that dot travel faster than the speed of light?
In Diagram form:
1
vote
3answers
87 views
Special Relativity - speed of light question
Just a basic question:
I know that if you are traveling at $x$ speed the time will pass for you slower than to an observer that is relatively stopped. That's all just because a photon released at the ...
0
votes
0answers
54 views
Determining Ether Drag - Aberration of Starlight
In order to determine the relative motion between the Earth and the ether (the medium through which light supposedly propagated. It has zero density and complete transparency), scientists used the ...
2
votes
3answers
137 views
What starts the movement of a photon
Although a photon has no (rest) mass, it does have a measurable speed. Its movement can be altered by gravity. A photon "travels". If I turn on a flashlight, seen by someone at a distance, the photons ...
1
vote
0answers
11 views
Speed of Light in a Medium [duplicate]
For light travelling in a medium with refractive index greater than one:
The "average" speed of light is slower than the speed of light in a vacuum. As far as I know, the instantaneous speed of light ...
-2
votes
2answers
106 views
If we are travelling with the speed of light, can we see what's behind us? [closed]
If we are travelling with the speed of light, can we see whats behind us(like if we are moving away from earth can we able see the earth)? And how we see the things that we are approaching with speed ...
9
votes
2answers
704 views
Is the “How to break the speed of light” minute physics video wrong?
I am referring to this video, on YouTube, by minutephysics, which has quite a lot of views.
In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the ...
4
votes
1answer
160 views
Photons arriving from the Sun
Given that the Sun is a bit less than 10 light minutes away from Earth, is it correct to assume in principle (I understand actual processes in the core of the Sun make the situation at a photon's ...
-5
votes
3answers
186 views
Could some Red and Blue shifts be the result of light passing through “dark matter”?
As i see it, light behaves in certain ways, as the Double Slit experiement shows,
So when light comes into contact with dark matter, it becomes both a wave and a particle, the wave is bent around the ...
0
votes
2answers
556 views
If nothing in the universe can travel faster than light, how come light can't escape a black hole? [duplicate]
Possible Duplicate:
How does gravity escape a black hole?
If nothing in the universe can travel faster than light, how come light can't escape a black hole? I mean, Einstein's relativity ...
1
vote
1answer
147 views
Speed of light and virtual particles
After becoming extremely bored while studying for an Afrikaans exam, I started thinking about virtual particles. So, can light (photons) interact with virtual particles (even though they only exist ...
-1
votes
2answers
165 views
A light and magnetic mirror paradox?
If light is an electromagnetic wave and lightspeed is constant (we ignore spacetime or gravity for this question) why can't we slow down light with a few dozen wellplaced magnets and electricly ...
4
votes
4answers
719 views
What happens when a photon hits a mirror?
When a photon of light hits a mirror does the exact same photon of light bounce back or is it absorbed then one with the same properties emitted? If the same one is bounced back does it's velocity ...
2
votes
1answer
354 views
Rotating mirror - Foucault's measurement of light speed
Some time ago I came across a secondary web source on measurement of light speed in water made by Foucault around 1850. I append its redrawn scheme below (light is reflected from the rotating mirror ...
0
votes
1answer
96 views
Is the acceleration and deceleration of a wave instantanious?
When an light travels in free space, it has a velocity of propagation equal to the speed of light.
However, then the light enters a medium with a refractive index of n, the velocity of propagation ...
-1
votes
3answers
166 views
Does the Lorentz transformation not apply to light?
Since you would know that light always travels at the constant velocity with respect to all frame of reference ....according to relativity whenever we are traveling at speed of light our time with ...
0
votes
1answer
125 views
How was Dorsey able to measure speed of light with 3 significant digits?
How was Dorsey able to measure speed of light with 3 significant digits in the year of 1907?
-3
votes
1answer
103 views
Why is neutrino beam not considered light?
I am trying to understand why physicists consider a neutrino beam not to be light.
Here's the research that I did to find the answer:
...
1
vote
4answers
312 views
The speed of tachyons
The other day I was wondering: When a tachyon is coming towards you faster than the speed of light, will you see it before it hits you? Then I thought of course not, since the light waves aren't ...
2
votes
1answer
130 views
The range of light
It occurs to me that the empirical evidence shows that there is a point out in space where light stops coming from.
Putting aside the expansion of the universe for a second, and focusing strictly on ...
7
votes
4answers
1k views
Why is the speed-of-light “the upper limit” rather than the speed of “particle type X”?
Basically, I can't stop wondering why light (the photon) is so special, compared to all the other particles known (and unknown) to modern day physics.
Could it be that there exists an upper limit on ...
2
votes
3answers
466 views
High speed and low speed photons
Looking at the discovery of the neutron, and I came across this page: http://www-outreach.phy.cam.ac.uk/camphy/neutron/neutron3_1.htm
The animation on the left, talks about low energy photons and ...
9
votes
5answers
3k views
Why can't light escape from a black hole?
Photons do not have mass (that's why they can move at speed of "light").
So, my question is how the gravity of black hole can stop light from escaping?
13
votes
4answers
428 views
What is the mechanism behind the slowdown of light/photons in a transparent medium?
So light travels slower in glass (for example) than in a vacuum. What causes light to slow down? Or: How does it slow down? If light passes through the medium, is it not essentially traveling in the ...
