All Questions
Tagged with spacetime speed-of-light
189
questions
2
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161
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When you are in a gravitational field, do object far away get physically closer to you as you get closer to the mass?
An observer A is close to a black hole and an observer B one light year away. They are both remaining at constant radial distance from the black hole. A is at 2 Rs away from the center of the black ...
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0
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1
answer
54
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Proof of the invariance of $c$ using the Lorentz group
Apologies if this question was already asked a few times but i could only find proofs of the invariance of $ ds^2 $.
Is there any way of proving the 2nd postulate (that $c$ is invariant in all ...
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votes
2
answers
102
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Can we use the fabric of spacetime to go faster than the speed of light?
If the fabric of spacetime isn't bound by the limit of the speed of light (the universe is expanding faster than the speed of light), could humans somehow wrap a spaceship in a bubble of the fabric of ...
12
votes
5
answers
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Could relativity be consistent if there are multiple light-like fields with different invariant speeds?
My understanding of real physical theory of electromagnetism goes like this:
The Maxwell equations can be used to derive the speed of light;
$$\nabla\cdot\textbf{E}=0$$
$$\nabla\cdot\textbf{B}=0$$
$$\...
- 5,148
1
vote
2
answers
132
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Do events very far away happen in a different timeline?
I am not sure how to ask this question in a concise manner so I am sure somebody out there explained it but I cannot seem to find it.
So I recently watched some videos explaining that $c$ not only ...
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1
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90
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Question about the norm of the four-velocity being equal to $c$
On the way to the Einstein equation we derived the four-velocity:
$$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 ...
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1
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76
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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 ...
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2
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60
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Time dilation query [closed]
In the light clocks, time ticks via the motion of light and since speed of light is constant therefore when the clock is in motion ,the photon has to cover a greater distance by the perspective of an ...
23
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7
answers
5k
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Is there a *geometric* explanation for why photons have no rest frame?
I've read the various threads on this site that talk about it being impossible for photons (or massless particles in general, really) to have a rest frame, and the answers all seem to boil down to &...
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2
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1
answer
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The value of speed of light in different regions of spacetime
This question of mine started shaping in my head first while I was looking for the most fundamental answer for the speed of light's value and its property of being the limit.
I have convinced myself ...
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0
votes
6
answers
218
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Speed of Light and Time [closed]
I'm an amateur and this is my first question here, I'm trying to formulate question about a general representation I have in mind after trying to grasp the idea of relativity and the concept of space-...
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2
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80
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Question on Special Relativity regarding light [duplicate]
Mine is a very basic question yet I haven't got a satisfactory answer so I turn to you. Special Relativity is based on two assumptions, one of which is that the speed of light is constant for all ...
0
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1
answer
67
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Can we observe a more recent space?
The space we are viewing now is their distant past as their light has only reached our eye or telescope after travelling a long distance at the speed of light. However, for lights that are still on ...
2
votes
0
answers
179
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An interpretation of special relativity? [closed]
Consider a 4-dimensional space $\mathrm{S}$ in which all objects move at the same speed $c_S$ but in different directions. For the objects A and B that move in directions $\overrightarrow{u_A}$ and $\...
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3
votes
1
answer
106
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How does the second postulate of special relativity imply invariance of spacetime interval?
I have trouble understanding why the second postulate of Special Relativity implies the invariance of spacetime interval $\Delta s^2=-c^2\Delta t^2+\Delta x^2+\Delta y^2+\Delta z^2$.
Suppose we have ...
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1
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89
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Are length and time mathematically equivalent scales? [closed]
So, say we define a clock as measuring an electronic oscillation on a quartz atom, eg, a normal clock.
The fine structure constant is a relation between the electron mass and C. If C goes up, electron ...
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1
vote
1
answer
112
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How to show mathematical equivalence between the idea of relativistic mass and the geometric explanation of why massive objects can't reach $c$?
I've frequently seen two different explanations for why, in SR, it's impossible for an massive object to reach $c$:
As a massive object approaches $c$, its kinetic energy starts being converted to ...
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0
answers
24
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Does time slow down for light according to relativity? [duplicate]
According to Einstein's theory of relativity
Time slows for a individual who moves at the speed of light and time goes backward if the individual is faster than the speed of light.
So , is it that for ...
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0
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0
answers
40
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Twin paradox symmetry in time dilation during the first leg [duplicate]
I was watching this Ted Ed video on Youtube about the twin paradox and found the explanation with the spacetime graph a bit confusing. At 3:00 in the video, they show a graph and explain how bursts ...
0
votes
1
answer
131
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Relativistic Mass Relative to a Stationary Observer
I know what you’re thinking, “Not another question on Relativistic Mass.” I’ve spent the better part of a day going down the general and special relativity rabbit holes, and I can not find where this ...
-1
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1
answer
112
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What speed of light means? [closed]
speed of light means moving through space with the same speed you move through time?
or to move "only" through space and not through time?
Does this mean that you exist in two (or more) ...
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1
answer
83
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Can you experience multiple points in time at a specific point in time? [closed]
So from my understanding, light takes time to travel to our eyes. So everything we see is from the past, right? So does that mean that at a specific point in time, we are seeing simultaneously a point ...
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3
votes
2
answers
418
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Converting Seconds to Millimeters
The concept is that time is another dimension, complementary to those we can observe and measure directly. For those three, I can take a ruler and measure how many millimeters one point in space is ...
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3
answers
200
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Is it possible to prove from relativity that massless things have proper time of zero?
Is it possible to come to the conclusion that something massless has proper time of zero, thus moves at $c$? I have seen many arguments for why moving at the speed of light means proper time is zero, ...
- 1,261
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2
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61
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Can Shapiro Time Delay cause light in a vacuum to go faster than c as viewed from a remote reference frame?
I know within any reference frame the speed of light is fixed. But it has been shown that light does appear to slow down when passing massive objects as viewed from a remote reference frame per https:/...
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1
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1
answer
80
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Why is the time part of the space-time with exactly second degree?
Why is exactly $n = 2$ in the equation
$$\begin{array}{*{20}{c}}
{{{\left( {ds} \right)}^n} = {{\left( {c \cdot dt} \right)}^n} - {{\left( {dr} \right)}^n}}\\
{dr = \sqrt {{{\left( {dx} \right)}^2} + {...
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1
answer
39
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Does local gravity change when approaching the speed of light? (Relativistic mass) [duplicate]
Let's say we'd transform earth into a giant space ship and had some planetary drive that can accelerate it without burning any kind of fuel (so the amount of matter on earth stays the same - we'd ...
6
votes
2
answers
531
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Does kinetic energy of an object curve spacetime? [duplicate]
Based on general relativity mass and energy distribution curves spacetime. Thus, if an object with 1kg rest mass moves with constant speed and has a speed very close to speed of light, then it has an ...
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1
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2
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274
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Time and speed of light in Relativity
Time running slower near a massive object, but the speed of light does not really change near a massive object, according to Relativity - it just curves. Is not time directly related to the speed of ...
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2
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117
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How would the following image look like, if we didn't use $ct$ for time?
I just wonder how spacetime would look like if we didn't use $ct$ for $t$ and we just used $t$ instead?
I guess the $t$-axis would just scale. Would that mean that, the hyperbolas would be very hard ...
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2
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3
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174
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Perception of light speed when traveling between two light sources
I'm struggling with a fundamental understanding of time dilation and special relativity (if I'm correct).
Many online sources explain it as the following:
With the ship moving away from the lightbeam ...
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4
votes
3
answers
759
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Constant speed of light violates accelerating expansion of universe?
My question regards the following:
One of the most fundamental principles of Einstein's GR is that all free bodies move through spacetime with constant velocity $c=1$.
However, in 1998 Hubble showed ...
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1
vote
3
answers
136
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Measuring the Hubble Constant
Attempts to measure the expansion of the universe have come in various forms. The recent Cosmology Crisis (https://www.space.com/why-is-there-a-cosmology-crisis) has me pondering the expansion rate ...
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1
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195
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Lorentz transformation equations: an insight [closed]
Let Bob be moving towards the positive $x$-axis and Alice be stationary at the origin. Then the Lorentz transformation gives:
$$t' = \gamma\left( t- \frac{v x}{c^2}\right)$$
where $t'$ is the time of ...
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6
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If you travel on car with nearly the speed of light and turn on the car headlights: will it shine in gamma light instead of visible light?
If you travel on car with nearly the speed of light and turn on the car headlights: will it shine in gamma light instead of visible light?
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1
answer
86
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Time dialtion when objects run in the same direction
Just trying to understand the basics.
I saw some videos claiming that when you run towards light the speed of light may appear to be faster than C therefore time corrects it by being slow.
Now the ...
user325851
-2
votes
1
answer
76
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Two spaceships traveling through spacetime and meeting at the same exact position and time
We have spaceship "A" traveling at a velocity of 99% of the speed of light for 2 seconds in the positive $x$-direction and then traveling at a velocity of half the lightspeed for 1 second in ...
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2
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168
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How speed of light is absolute/constant if time (denominator) is relative?
Speed is path / time.
How speed of light in vacuum can be always constant if denominator (time) is relative, its changing?
If speed of light must be constant then path must be changed as well?
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1
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42
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Making use of principles concerning relative and absolute velocity, can we move an object at a velocity that is greater than light?
I am new to physics, so please do not get angry if this is a stupid question.
First, let's imagine that we are sometime in the future where we have an extremely fast spaceship which is travelling in ...
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1
vote
2
answers
95
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Does it make sense to create a spacetime diagram in respect to another velocity besides the speed of light?
I'm trying to understand the application of special relativity into things where it's velocity might be none regular units. Just for argument sake, let's say that the distance is measured in some unit ...
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3
answers
390
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This question is about time dilation but a bit different
See the image below-
Here I have decribed a scenario related to relativity theory. A spaceship is travelling at "V" velocity relative to a man standing on planet. The Spaceship's frame is ...
1
vote
1
answer
50
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Speed of light measurement using a star mass, just like a satellite orbits the earth
This is just an idea than came to my mind last night, would it be possible to, launch a satellite, close enough to the sun (To be safe for it) to light a laser, somewhere close enough to the sun, ...
0
votes
2
answers
124
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If we find a star exploding 100 light years away, that means it happened 100 years before? [duplicate]
So can someone please help me with this? Can someone make the answer as simple as possible?
So my question is if we see a star exploding like 100 light-years away, that means that star exploded 100 ...
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votes
3
answers
189
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Is the speed of light the limit or just everything moves at this speed?
When I was a little kid, I was fascinated by the fact that we are not able to surpass the speed of light. I imagined a giant spaceship trying to catch a light beam like superman tries to catch flash.
...
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1
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209
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Is This Why the Speed of Light is Universally Invariant?
Please could you tell me if the following is an original thought or whether this is already understood. I ask because I am undertaking a piece of writing on the nature of spacetime. What I discuss ...
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1
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59
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Does light travel same distance in same time not depending of the path orientation regarding Earth's surface?
Does light travel the same distance at the same time regardless of the path orientation? The light in the proximity of a gravitational source can bend its trajectory and frame-dragging can cause the ...
- 2,255
1
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1
answer
55
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Is there a hyperplane hyperbolic orthogonal to a light-like curve?
In Special Relativity, a hyperplane that is hyperbolic orthogonal to a worldline at a point p can be viewed as the simultaneity plane with respect to the worldline at p. What if, however, the ...
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3
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603
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Is time taken by light to travel any distance 0 or finite? [duplicate]
According to relativity, Light does not experience any time. So it must travel any distance in no time.
But, we know that light has finite speed $c$. So it should take finite time.
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1
answer
1k
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How can we perceive light if light doesn't move through time? [duplicate]
From my understanding in space-time everything moves at the speed of light $c$ in some direction of this four dimensional space. Light itself moves only through space, so it doesn't move at all in ...
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3
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166
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Is there an exact constant value for the speed of light in a vacuum distorted by a gravitational wave?
In a vacuum, construct a cylinder of photons arranged as follows:
A 'measuring apparatus' computes the speed of light as 299,792,458 m/s.
However, suppose the vacuum is distorted by a gravitational ...
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