# Light's Speed & Moving Observer: What Happens?

• B
• danielhaish
In summary: If you are imagining a moving star, then the light from the star would be moving too. However, according to special relativity, the speed of light is the same in all frames of reference.
danielhaish
for example the car headlight would look faster then c speed. (it speed would be the speed of light +the speed of the car) to observer in front the car.
because the light come from the car so the speed of the car would connect with light speed (like when you walk on a train) .
so does the light wave go slower then the c speed in that case? when the source of light is moving .

Last edited:
Pleas reformulate these as rational thought. Faster than what? slower than what?

etotheipi, Vanadium 50 and danielhaish
hutchphd said:
Pleas reformulate these as rational thought. Faster than what? slower than what?
is it batter now?

Not really.

danielhaish and etotheipi
Vanadium 50 said:
Not really.
I edit it again

danielhaish said:
for example the car headlight would look faster then the speed of light (the speed of light +the speed of the car) to observer in front the car.
because the light come from the car so the speed of the car would connect with light speed (like when you walk on a train) .
Walking on a train doesn't work the way you are thinking. The train is moving at 50 km/hr, you're walking up the aisle at a speed of 5 km/hr relative to the train, you are NOT moving at 55 km/hr relatove to an observer on the ground.

Search this forum and google for "relativistic velocity addition"

Nugatory said:
Walking on a train doesn't work the way you are thinking. The train is moving at 50 km/hr, you're walking up the aisle at a speed of 5 km/hr relative to the train, you are NOT moving at 55 km/hr relatove to an observer on the ground.

Search this forum and google for "relativistic velocity addition"
I know so I am asking weather the speed of light connect with the speed of the car relative to observer on the ground? because as you said your speed and the train speed connect relative to observer on the ground

danielhaish said:
I know so I am asking weather the speed of light connect with the speed of the car relative to observer on the ground? because as you said your speed and the train speed connect relative to observer on the ground
The speed of light, by the postulates of SR and as confirmed by experiment, is ##c## in both the ground frame and the car frame of reference.

cianfa72 and danielhaish
PeroK said:
The speed of light, by the postulates of SR and as confirmed by experiment, is ##c## in both the ground frame and the car frame of reference.
but what would happen to get this if the time on the car would go slower it wouldn't mind to outside observer it will steal experience that the light is going faster

danielhaish said:
but what would happen to get this if the time on the car would go slower it wouldn't mind to outside observer it will steal experience that the light is going faster
Something is lost in translation there.

If you want to understand how the special theory of relativity supports the invariance of of the speed of light then you need to study material on SR (special relativity).

danielhaish
Einstein worked this all out. If you are interested in learning about Special Relativity, please get a book and put in the effort.

PeroK said:
Something is lost in translation there.

If you want to understand how the special theory of relativity supports the invariance of of the speed of light then you need to study material on SR (special relativity).
I understand that if observer moves then it experience light slower but what if the light is coming from moving source how would it stay in the same speed relative to not moving observer

Last edited:
danielhaish said:
I understand that if observer moves then it experience time slower but what if the time is coming from moving source how would it stay in the same speed relative to not moving observer
Where are you learning SR? Your statements don't make much sense.

Times, distances, and therefore clock synchrony all depend upon frame of reference. You will not figure this out by asking a series of disjoint questions. It is a comprehensive theory and you need to take the time to study it comprehensively.

DaveE, PeroK and danielhaish
PeroK said:
Where are you learning SR? Your statements don't make much sense.
I saw it on youtube video . and sorry meant to type if the light coming from moving source . but imagine that a star is going a way from us how can the light coming from stay in the same speed relative to us

danielhaish said:
I saw it on youtube video

You should not be trying to learn physics from pop science sources. You should be learning it from a textbook. Taylor & Wheeler's Spacetime Physics is a good textbook for SR.

danielhaish said:
imagine that a star is going a way from us how can the light coming from stay in the same speed relative to us

Because velocities in relativity don't add linearly. You have already been told to look up "relativistic velocity addition". All textbooks on SR discuss it.

vanhees71
@danielhaish , we try to be understanding of people whose first language is not English. But we are in a situation where we don't understand your questions and you don't understand our answers. And that's not helping anyone.

The suggestion to get a text is a good one, and I would amend that to "a text in your native language".

vanhees71
I think I found answer that connected to doppler low but I am not sure

danielhaish said:
for example the car headlight would look faster then c speed. (it speed would be the speed of light +the speed of the car) to observer in front the car.
No. You are using here the classical velocity addition ##u=u'+v##. Instead, you must use the relativistic formula:
##u = \frac{u' + v}{1+ u'v/c²}##

If you set ##u' := c##, what is the result for ##u## ?

Source (see "Eq. 10"):
https://en.wikipedia.org/wiki/Special_relativity#Lorentz_transformation_of_velocities

P.S.
The same is valid for your thread from March.

danielhaish and PeroK
danielhaish said:
I think I found answer that connected to doppler low but I am not sure

The relativistic Doppler effect tells how the frequency and wavelength of light depend on the source's motion relative to the observer. The relativistic Doppler effect formula assumes that the speed of light is ##c## regardless of the source's motion relative to the observer.

vanhees71 and danielhaish
To summarize in simple terms:

It does not matter if whatever created that light is moving away from you
It does not matter if whatever created that light is moving towards you
It does not matter the speed at which whatever created that light is moving

The speed of light is always C in ALL directions!

For example: If you had 2 spaceships that travel at 0.6C moving in opposite directions from each other and one emits a beam of light, that beam of light will still get to ther other ship as it's still moving faster than the ship going in the opposite direction.

danielhaish

## 1. What is the speed of light?

The speed of light is approximately 299,792,458 meters per second in a vacuum. This is considered to be the fastest possible speed in the universe.

## 2. How does light's speed change when observed by a moving observer?

According to the theory of relativity, the speed of light remains constant regardless of the motion of the observer. This means that the speed of light will appear the same to a stationary observer and a moving observer.

## 3. What is the difference between the observed and actual speed of light for a moving observer?

For a moving observer, the observed speed of light will appear to be the same as the actual speed of light. However, the path of light may appear to be curved due to the observer's motion.

## 4. Can light's speed be exceeded by a moving observer?

No, the speed of light is considered to be the maximum speed in the universe. It cannot be exceeded by any observer, regardless of their motion.

## 5. How does the speed of light affect time and distance for a moving observer?

The speed of light is a fundamental constant in the universe and is used to define the concept of time and distance. For a moving observer, time and distance may appear to be different due to the effects of relativity, but the speed of light remains constant.

### Similar threads

• Special and General Relativity
Replies
45
Views
3K
• Special and General Relativity
Replies
33
Views
2K
• Special and General Relativity
Replies
9
Views
383
• Special and General Relativity
Replies
25
Views
3K
• Special and General Relativity
Replies
57
Views
4K
• Special and General Relativity
Replies
1
Views
689
• Special and General Relativity
Replies
21
Views
463
• Special and General Relativity
Replies
2
Views
459
• Special and General Relativity
Replies
7
Views
1K
• Special and General Relativity
Replies
3
Views
1K