The speed of light is a fundamental universal constant that marks the maximum speed at which energy and information can propagate. Its value is $299792458\frac{\mathrm{m}}{\mathrm{s}}$.

learn more… | top users | synonyms

0
votes
0answers
35 views

Explanation about the speed of light according to Maxwell from the book : “ A brief History of Time”

I just started reading Hawking's book: " A brief history of time" and there is a section that I don't understand referring to the speed of light moving through the "ether". In the second chapter, ...
0
votes
1answer
40 views

Cold Solid Matter at the End of a Black Hole's Acceleration Disk?

Is it possible that black holes magnetic field are rapidly cooling matter using a type of magneto caloric effect and cold fusion creating new matter only possible with a black hole's gravity? A type ...
1
vote
1answer
39 views

Is light relative?

I was wondering, if two cars (A and B) are going at different velocities let's say A=90km/h, B=80km/h then if we add the two speeds we get 170km/h meaning they are relative to each other. But if one ...
1
vote
0answers
20 views

How can you find the $u$ using time dilation if you only know $\Delta t_o$?

I've come across two problems dealing with time dilation now that ask how fast should an astronaut go in order to travel EG: 400 LYears in 10 Years. What I can not wrap my head around is how this is ...
1
vote
2answers
92 views

Why does time stop its flow? [duplicate]

According to the "list verse" time gets to a pause when someone or something travels at the speed of light. But a question still lies in my mind, if time always travels forward and does not stop at ...
0
votes
1answer
62 views

Interpretation of time dilation

Is there any interpretiation of time dilation for photons? I mean, how does time work for them? Do photons have any distinction between their own and observer's time? Or is it something like ultimate ...
3
votes
2answers
74 views

Help understanding why can't we measure absolute velocity?

(This is probably a clone of some other question, but I haven't been able to find a satisfactory answer, so I hope this is okay.) So, I know that in special relativity, there's no such thing as a ...
3
votes
3answers
276 views

Why isn't a Photon justified in concluding that it is at rest and everything else is moving past it at c? [duplicate]

Why isn't a photon moving at c not justified in concluding that it is at rest and everything else is moving past it at c since relativity postulates that the laws of physics are invariant (i.e. ...
1
vote
1answer
35 views

light in black holes and space time

I watched videos, read articles, learned a lot about black holes and got confused: Lets say that a light is doing its way inside a black hole toward the singularity. If it's inside the event ...
1
vote
1answer
51 views

Implication of Relativity [duplicate]

According to relativity, no useful matter can travel faster than light. Suppose that your are a light beam travelling. Now you have a parallel light beam travelling beside you. Suppose you look at the ...
0
votes
2answers
79 views

Speed of light invariance (once again)

The answer to this very good question seems to be favored by a large amount of users. Yet it seems to imply that the constancy of the speed of light and its finiteness stems from the underlying ...
1
vote
0answers
38 views

Impossible? Or not? [closed]

If the universe is expanding at light speed, and you stand on the edge moving out, if you look across the universe, then you will see twice the light speed, why is that?
0
votes
2answers
85 views

If our eyes see at the speed of light, how do we know about the current states of stars and galaxies far away?

As you guys know that we see at the speed of light, it means that we see the past of stars and galaxies. So say a star went supernova right now, how are we able to know current state of that star that ...
-1
votes
1answer
59 views

Field of view from travelling at (almost) the speed of light?

As we go faster, our field of view increases, but would happen if we travelled at (almost) the speed of light? My questions: Can we see a 360 degree view while travelling at (almost) the speed of ...
14
votes
3answers
2k views

Can we tell when an established theory is wrong?

I was reading the following answer from this question: In physics, you cannot ask / answer why without ambiguity. Now, we observe that the speed of light is finite and that it seems to be the ...
1
vote
0answers
60 views

Would a “better” speed of light be possible? [closed]

The vast distances in space make it almost impossible to reach anywhere in a reasonable timeframe, since we have the speed of light as an upper bound and even getting close to that speed takes a lot ...
1
vote
1answer
57 views

Thought experiments about c [closed]

Poincarre had a brilliant thought about what if everything in the universe doubled in size , would anybody notice any difference or even be able to measure anything that can be compared with previous ...
-1
votes
1answer
30 views

Can absolute speed of object be measured? [closed]

Let's say there are two objects in space - Station and huge non-transparent sphere. Sphere starts to move from station 5000 km/h. Inside the sphere, beam of light is produced in direction the sphere ...
1
vote
3answers
84 views

Why is the speed of light not 3 x $10^{8}$ m/s, or why not a round figure for the meter [duplicate]

This question is not about why the speed of light is not greater than 299,792,458 m/s. It's about why it's that exact value. This was a question from a book(I know homework questions are frowned upon ...
1
vote
0answers
25 views

How much is the maximum posible information travel speed in medium?

Light has slower speed in medium. Should we consider this when we use special relativity in atmosferic(or any other type of medium) motions? If we should use vacuum light speed, does it mean photons ...
2
votes
1answer
56 views

Gravity is Instant [duplicate]

Without being able to manipulate gravity. How do we know that gravity is restricted to the speed of light? or gravitational effects from an exploding star would be felt (if we were near) before we ...
-1
votes
1answer
105 views

Speed of light or speed of time?

Proxima Centauri is about 4.22 Light Years, so if there is anyone that could see us, the image of us would be 4.22 years old, if we depart at 99.99% the speed of light we would arrive almost instantly ...
-2
votes
1answer
64 views

Constancy of speed of light in vacuum? [closed]

Have scientists tried their best to calculate speed of light in vacuum? It seems very absurd to me that light of all frequencies have same velocity in space. Can someone find in future if this speed ...
157
votes
18answers
24k views

Do we know why there is a speed limit in our universe?

This question is about why we have a universal speed limit (the speed of light in vacuum). Is there a more fundamental law that tells us why this is? I'm not asking why the speed limit is equal to ...
2
votes
1answer
100 views

Is near light speed travel possible? Likely?

I was contemplating the possibility of sending an interstellar probe that can produce results in a reasonable time frame. For such a mission to be realistic, the spacecraft would have to travel at ...
2
votes
6answers
154 views

Light in mass moving at high velocity

Imagine if you will, a strand of fiber optic cable 186,000 miles long. A pulse of light is sent through the stationary cable: it takes 1 second for light to travel the entire length of the cable. Now ...
-3
votes
3answers
54 views

Is mass directly or inversely proportional to time? [closed]

From a Newtonian perspective: F = ma F dx = ma dx E = m (dv/dt) dx m = (E dt) / (dv dx) Mass is directly proportional to time, if time slows down then mass goes down or decreases. From a ...
1
vote
0answers
25 views

Variable speed of light impact on spectral absorption lines in distance luminous objects?

There are many other arguments as to the constancy of the speed of light (or more precisely, c). One thing I have been curious is what would the impact be on spectral measurements from distant ...
0
votes
1answer
35 views

Time and velocity

Suppose two cars are traveling at a velocity of $c/2$ ($c$=speed of light) in two straight lines parallel to each other but in opposite direction in vacuum. Then what will a person sitting in one of ...
2
votes
1answer
42 views

Variable speed of light in loop quantum gravity

Loop quantum gravity predicts a variable speed of light. What is the range of such a variation in its speed?
3
votes
1answer
101 views

Is it experimentally proven that photons travel at speed $c$ in vacuum?

Are there experiments which show that single photons (not classical em waves) travel exactly at $c$ in vacuum? What is the error bar in that case? The question is posed due to the fact that loop ...
2
votes
1answer
154 views

Slow light that does not go back to it's original speed in vacuum [closed]

I have watched today episode of scishow where Hank claims that photons can be permanently slowed down to speed that is less than speed of light. ...
0
votes
2answers
134 views

Is it possible to go faster than the speed of light in vacuum?

If it is possible for particles to go faster than the speed of light in certain events, would it be possible to create a situation in which the barrier of the speed of light can be crossed?
0
votes
0answers
39 views

Does time dilation affect the speed of a moving object?

Imagine you are traveling at 99% of the speed of light. Will the speed of the moving object slow down for both objects and for the resting observer or either one?
-2
votes
1answer
53 views

Objective velocity (Relativity theory) [closed]

Suppose that I have a velocity of (approximately) $c$. Then I decelerate with $c$ per hour for exactly one hour. Then I would know that I would be standing still in the end, because the decelleration ...
0
votes
2answers
61 views

Does the speed of light differ for two frames moving at different speeds relative to an non moving observer?

Wikipedia says that: The speed of light in a vacuum is the same for all observers regardless of the motion of the light source. How can this be true and and returning to my question, if there is ...
2
votes
1answer
78 views

Is this argument valid as to why we can (not can't) reach the speed of light?Please do explain [closed]

I have already asked this question on quora, with difficulty but I have not yet obtained a "works for me" answer. Please discuss with me about this.:) Q:Why can we not touch the speed of light? ...
2
votes
3answers
99 views

Light cone argument for speed of light

Using light cones to state that nothing can travel faster than light to me seems like a flawed argument. (I understand other reasons why the speed of light cannot be broken.) However, it seems to me ...
1
vote
3answers
91 views

If photon can bend spacetime how does it exchange graviton?

Say two photons moving beside each other through space at speed of light, since it carries energy it can bend spacetime. So both photons will exert gravitational force on each other at speed of light ...
4
votes
4answers
218 views

Can there be acceleration without velocity?

If I was in a spaceship continually accelerating at $9.81m/s^2 =1g$ in a straight line, I would reach near light speed within a year. On Earth, we are in a gravitational field of $1g$, which ...
1
vote
0answers
20 views

Is photon massless? [duplicate]

if photon is massless then in E2=m2c4+p2c2 is m=0 ? and p=mv1-mv2 shouldnt be zero too. if both the statements are true then does photon has no energy?
1
vote
0answers
32 views

Highest temperature [duplicate]

The temperature of a body varies with the KE of its particles. The maximum KE can be obtained by making the atoms move about near the speed of light. Let us take the body as a gas so that the body can ...
0
votes
0answers
36 views

Is a Battery to store photons possible?

@MISC {55768, TITLE = {Why can't we store light in the form of light?}, AUTHOR = {AldCer (http://physics.stackexchange.com/users/20409/aldcer)}, HOWPUBLISHED = {Physics Stack ...
0
votes
1answer
35 views

Perfect vacuum in experiment [closed]

When conducting experiments to determine the speed of light in a perfect vacuum does that vacuum(?) replicate outer space?
1
vote
0answers
29 views

Getting an object to travel at or near light speed by adding velocities [duplicate]

Firstly I'll just give a brief example of where my query came from. I was watching the episode of Futurama where Bender meets God after being fired from the planet express ships torpedo tube. The crew ...
1
vote
0answers
39 views

Special Relativity and Space travel [closed]

I'm doing a science project on space travel where I have to include a part about special relativity and how time acts when you're traveling in space with high speed. I'm not really sure where to start ...
6
votes
1answer
112 views

A question about gravity [duplicate]

Some time ago I encouraged by 11 year old son to watch Cosmos: A Spacetime Odyssey with Neil DeGrasse Tyson, and subsequently Cosmos: A personal Voyage with Carl Sagan, as well as other astronomy ...
1
vote
1answer
89 views

Application of Heisenberg's uncertainty principle on photons

While I was hobby-reading about quantum mechanics I came across Heisenberg's theory. But while I was trying to understand it I thought of this: if the speed of light (as well as the momentum of a ...
-2
votes
1answer
74 views

Do photon inside event horizon exceeds speed of light?

Event horizon is a region of space whereby nothing with information can escape, so I imagine that a photon falls into this region of space does it accelerates toward the singularity if it exists? Do ...
-1
votes
1answer
60 views

Atoms traveling at the speed of light [closed]

If an atom was to travel at the speed of light (although impossible), wouldn't the nucleus break apart? I say this because the particles holding the protons together in the nucleus wouldn't be able to ...