Questions tagged [speed-of-light]
The speed of light is a fundamental universal constant that marks the maximum speed at which energy and information can propagate. Its value is $299792458\frac{\mathrm{m}}{\mathrm{s}}$.
2,809
questions
0
votes
0
answers
8
views
Time dilation and gravity
Is time dilation a by-product of an object's mass bending the space-time or is it that the presence of the mass somehow interferes with the flow of time, thereby making disturbances in it and is ...
0
votes
2
answers
49
views
Relativistic Doppler Shift vs Classical Doppler Shift Contradiction
In classical/Newtonian mechanics, the doppler shift (for light) can be expressed as:
$$ \frac{f_r-f_s}{f_s}=\frac{1+\beta}{1-\beta}-1 $$
In relativity the doppler shift can be expressed as:
$$ \frac{...
-2
votes
2
answers
71
views
Amateur Shower Thought Question About Time and Space
Apologize in advance if this is the wrong group. I often watch Netflix shows about blackholes explained in a nutshell or laymen’s terms.
I had a recent thought/scenario that may relate to some ...
- 99
0
votes
2
answers
74
views
What if an object is approaching us at near the speed of light?
Suppose an object that is 100 light years away is approaching us at 0.99c. It would take about 100.1 years for the object to reach Earth. But the light that this object emitted when it began the ...
- 101
3
votes
1
answer
52
views
Can two laser diodes of the same type and wavelength, be synchronized to emit light in the same phase, while working in a CW mode.?
Can two laser diodes of the same type, power and wavelength, be synchronized to emit light with lightwaves in the same phase, while working in a continuous wave mode (CW) ?
- 140
1
vote
1
answer
54
views
Thermodynamics and Special Relativity [closed]
What happens to the temperature of a body (not in the body frame) as it approaches the speed of light? My thinking is that the molecules will necessarily 'prefer' (as a natural consequence of the ...
- 11
2
votes
2
answers
366
views
Why can't we see past the observable universe?
Why can't we see light from beyond the observable universe?
I've done a lot of research on this and all I've found is unsatisfactory answers and straight up nonsense.
Some claim that the universe &...
- 131
0
votes
1
answer
32
views
Can Sagnac effect be observed in coiled, rotating electrical cables conducting electric signals?
Can Sagnac effect be observed in coiled, rotating electrical cables conducting electric signals, in a similar way to that observed in coiled, rotating optical fibers? And if so then who demonstrated ...
- 140
-4
votes
0
answers
84
views
Is this experiment a valid way to measure the one-way speed of light? [duplicate]
Ok so my proposed experiment is as follows:
A light ray is emitted from a source (like laser)
When it's emitted the timer starts (there is only 1 clock in whole setup, which is a crucial aspect for ...
8
votes
2
answers
5k
views
At what speed does information move through the atoms of a rigid object?
How fast does information travel on particles? I thought if you move a iron bar from one end it would take the speed of sound to move its other end. For example, theoretically if you hold an iron bar ...
- 97
0
votes
0
answers
31
views
Is it legitimate to calculate a time bw 2 events using this method?
Imagine a rocket moving on a straight line, passing by me (observer on Earth) at constant speed $v$ and going straight towards an asteroid located at distance $L$ (from me).
At time $0$ (as it runs ...
- 187
0
votes
1
answer
27
views
Will light of 405nm wavelength behave in a single mode (SM) fiber , in multimode manner?
Since the wavelength of 405nm is substantially shorter than the wavelengths of 1310-1550nm, and since the ratio of the diameter of a single mode fiber core to the wavelength, at 405nm, is several ...
- 140
0
votes
1
answer
76
views
The effects of light needing to reach observers from observed objects
I know some special relativity, but the material that I've learned has always treated observers as being able to instantly view objects. In reality, the light from an object first needs to travel to ...
- 133
2
votes
1
answer
181
views
"Pure Energy" in special relativity and why does the rest energy follow from a derivation at the speed of light?
I'm currently studying special relativity by reading through the lecture notes of M. Fowler from the University of Virginia.
The famous equation $E=mc^2$ is derived by analyzing the work done by a ...
- 39
0
votes
1
answer
306
views
Amaterasu particle's secondary particles travel faster than the speed of light?
From this article in The Guardian
When ultra-high-energy cosmic rays hit Earth’s atmosphere, they initiate a cascade of secondary particles and electromagnetic radiation in what is known as an ...
- 109
0
votes
1
answer
62
views
Relativity of Simultaneity- Train Experiment with 2 Countries signing Contract
I am having a hard time understanding the implications of one of the popular variations of the thought experiments associated with Relativity of simultaneity. The example goes as follows. 2 countries ...
- 101
0
votes
2
answers
45
views
Why does the different speed of light in different media cause refraction?
Why doesn't light simply go more slowly without bending? Is there a macro phenomenon, say a stream of bullets, that will also bend as it changes from one medium to another or is light somehow unique?
- 2,150
3
votes
2
answers
111
views
One-Way Speed of Light and the Big Bang
Variations on this question have been asked a few times (e.g. here, here, and a few YouTube videos here and here). The claim seems to be that because we can only measure the round-trip speed of light, ...
- 106
0
votes
1
answer
84
views
Which experimental setup replicating Michelson-Morley experiment had the longest path of light?
After the Michelson-Morley (MM) experiment many scientists performed similar experiments using the original MM experimental setup, or different derivative experimental setups employing lasers and ...
- 140
3
votes
3
answers
1k
views
Relativistic Light Velocity
I'm lay about relativity and I want to understand how does $c$ does not change between frames of reference.
Imagine a train of length $L_0$ at a relativistic speed and a light beam inside it. For an ...
4
votes
5
answers
396
views
Is the speed of causality slower in water?
I've recently read that what most people learned to think of as the 'speed of light' is actually the 'speed of causality', and that light just happens to travel at that speed (through free-space.) I'...
- 455
-7
votes
0
answers
69
views
If the speed of light is a universal constant, how are photons massless? [duplicate]
Help me out here.
Edit: Yes I've seen the momentum terms in a similar question.
Claiming mass has two definitions i.e. mass at rest vs. mass in motion is not helpful nor is it likely correct.
...
- 1
0
votes
1
answer
55
views
Proper time vs null path
I've heard three seemingly contradictory facts, so apparently I'm not understanding at least one of them correctly.
"Proper time along a path is the time elapsed for a clock that travels along ...
- 13
0
votes
1
answer
59
views
Question about the norm of the four-velocity being equal to $c$
On the way to the Einstein equation we derived the four-velocity:
$$u^\mu=(c,v^k)$$ with $v^k$ being the 3-velocity, which can can be very low ($
|v|<<c$).
However, the square of the four ...
- 157
2
votes
1
answer
70
views
Do light's electric and magnetic components oscillate in physical space?
I have heard that light is a transverse wave which is necessary for effects like polarisation, but I am unsure of what exactly this means. Is this saying that light's electric and magnetic components ...
- 25
1
vote
0
answers
63
views
Does the speed of light increase when falling?
The Schwarzschild form has a singularity at the Schwarzschild radius. If we write the metric in another form, such as the Lemaître form, the singularity disappears. In the Schwarzschild form the speed ...
- 109
0
votes
0
answers
89
views
Questions regarding action at a distance
There seems to be two concepts in action at a distance
The existence of an mediating medium (energy or matter) through which action is transmitted
The finiteness of the speed at which the action is ...
- 941
-1
votes
1
answer
115
views
Relativistic momentum for light
In special relativity,momentum $p$ is defined by $\gamma mv$ where $\gamma=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}$. Again,we are aware of the relation $E^2=(mc^2)^2+(pc)^2$. Now,the momentum of light is ...
- 1,177
0
votes
3
answers
92
views
Moving at the same speed relative to electrons thus no current but seeing light being generated?
Imagine a situation where I'm moving at the same velocity as the electrons in a conducting wire. In this scenario, from my frame of reference, the electrons appear to be stationary and thus there is ...
- 3
0
votes
0
answers
107
views
Do photons moving at $c$ slow down when entering a medium or take a longer path and only appear to slow down and what happens to time? [duplicate]
Imagine a photon leaving a vacuum and entering a medium, say, air. I have 2 questions:
Some claim that the photon is slowed by the medium so its speed becomes less than $c$. Is that true or does ...
- 29
0
votes
0
answers
45
views
Does Color change happen under a prism? [duplicate]
I was watching this video.
It Showed that light ( green ) changes its color to red after incidence of light. I couldn't think of how this happens because light's color is dependent on frequency rather ...
- 431
0
votes
1
answer
64
views
Does light move as a wave because empty space has inertia?
If I drop a rock into a pond, a wave will propagate through the water from the location where the rock made contact. The wave will travel at a speed dependent on the density of the medium. As far as I ...
- 109
0
votes
1
answer
67
views
Is it more accurate to say space in a weaker gravitational field is contracted, or that time is faster?
Little thought experiment. An observer places a mirror and a clock 1 lightyear away from a black hole. He then goes in the black hole's gravitational field at a point where he sees the clock tick at 2 ...
- 11
0
votes
1
answer
90
views
Velocity of de-Broglie Wave
I have been trying to figure out the solution to this problem of finding the "velocity" of de-Broglie's wave. I have tried to see answers from countless sources but none of them helped. My ...
-5
votes
3
answers
96
views
If light had mass
Is there any way to know how fast would light be if it had a mass? Something like 0.000000178536 kg. At least a formula to help estimate it would help, i asked chatgpt and it said ''E = mc²
E = (0....
0
votes
3
answers
104
views
Time dilation questions [closed]
If we have two reference frames K and K' which are moving relative to one another, special relativity suggests that there would be time dilation. In K, time appears to pass slower in K', whereas in K' ...
- 27
0
votes
2
answers
98
views
If a photon is absorbed, does the associated wave function disappear instantaneously, or at the speed of light?
I came to this question while thinking about light with extreme wavelengths. Say we had light (em radiation) with a wavelength of 100's of thousands of kilometres and we absorbed a photon of it on ...
- 339
-1
votes
2
answers
35
views
Has the amount of force/energy required to counter gravity the same scaling as energy required to reach lightspeed?
First, I have no clue about physics outside of school so please don't mind if I use wrong terms in my question.
So on earth there is a force applied to everything towards the ground at $\sim 1g$, or $...
- 99
0
votes
0
answers
25
views
Can gravitational waves be compared with a sinking water phenomena?
Let say we have some water in the sink and open the closure.. The water starts to move towards it in a whirpool like manner.. If we have a table tennis ball and leave it near the hole of the sink it ...
- 2,223
-5
votes
2
answers
139
views
How can light have a speed when it devies what speed is?
For us to measure any movement, the "something" has to have a different position to some reference frame. now speed is defined by the amount of changed position( which we can tell by the ...
-4
votes
1
answer
79
views
What's the speed limit for things with mass?
So the speed limit of the universe is 299 792 458 m/s, but only massless things like photons can archieve this speed. Since things that have mass can reach 99.99999...% speed of light, does that mean ...
-1
votes
3
answers
174
views
How can Electricity travel at the speed of light?
If electricity is the flow of electrons, how come it can flow at the speed of light? Shouldn't how fast it moves be limited to a speed lower than the speed of light because it has mass?
- 57
1
vote
1
answer
94
views
Relativistic Velocity-addition formula adds a scalar to a vector?
Sorry if this is a stupid question.
The formula for relativistic Velocity-addition is
$u = (v + u') / (1 + (vu'/c^2))$
It seems that v, v', u, and u' are vectors, while c is a scalar.
But 1 seems to ...
- 807
0
votes
1
answer
92
views
Measuring one-way speed of light [duplicate]
Veritasium's video explains why we can't measure the one-way speed of light: https://youtu.be/pTn6Ewhb27k?si=60Q0AffVdt09lJSb
However, I still don't completely get why this is the case.
Let's say that ...
- 565
-5
votes
1
answer
75
views
What would happen if the aether did exist and there was no such thing as relativity? [closed]
I'm curious as to the purpose of relativity and why the universe would function this way as opposed to a universe with an aether. So what would be different if we had an aether?
- 333
0
votes
2
answers
198
views
What's wrong with this One-Way Speed of Light experiment? [duplicate]
I can't tell what's wrong with it.
Imagine the wheels of a car, jack the car, put a sensor on one wheel, a laser on another, start rotating, with enough speed the sensor will start to detect the laser ...
- 11
0
votes
1
answer
46
views
How to explain light traveling two distances in the same frame of reference? [closed]
Suppose I have a "moving" frame of reference where I send a light beam from point A to two equidistant points B and C (equidistant in the moving frame of reference). From a "stationary&...
0
votes
1
answer
50
views
Relativistic Effects on Electromagnetic Wave Propagation
So for a recent lab I had to calculate the length of a conductor by measuring the time it took a signal to reflect off of the open end. I used the very simple principle of $v=st$ and, knowing that the ...
- 1
0
votes
1
answer
68
views
All Michelson-Morley experiments have only been done in non-inertial conditions. Does special relativity apply or not?
As far as I know not a single Michelson-Morley experiment has been done in non-inertial conditions. Shouldn't it be general relativity that applies to Michelson-Morley experiments done so far?
- 31
1
vote
0
answers
53
views
Did the distances of the reflecting mirrors in Michelson Morley need to be precise to 100 nm or less?
When I took Physics, both in HS and College I was taught that the reason the Michelson Morley experiment "could" produce an interference pattern at the detector location was that the two ...
- 531