# The Naked Scientists Forum

### Author Topic: lights velocity  (Read 11546 times)

#### thebrain13

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##### lights velocity
« on: 14/07/2006 19:55:15 »
Does light always have to move at c from you, even if its not traveling directly towards, or away from you? For example, if you drew a line from you, to a photon one light year away, and the photon was traveling perpendicular to the line. Would the photon be seen as traveling c from you, or at c from its starting point?

#### xpowderx

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##### Re: lights velocity
« Reply #1 on: 14/07/2006 22:49:43 »
If C is moving from a-b then the moment the observer takes notice it would be in neither.

#### Soul Surfer

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##### Re: lights velocity
« Reply #2 on: 14/07/2006 22:55:30 »
You only detect light if it is travelling towards you. If there is a confined beam of light going in a different direction at a distance you will only detect it if it interacts with something like smoke particles and scatters light in your direction  this light of course will be travelling towards you.  So the question does not arise.

Learn, create, test and tell
evolution rules in all things
God says so!

#### thebrain13

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##### Re: lights velocity
« Reply #3 on: 15/07/2006 03:32:23 »
Many of einsteins thought experiments, featured light that never hits you. Take his thought experiment on relativity of simultaineity for example. He says lightning strikes simultaneously on two lightning rods, mounted on top of a train, both are placed at an equal distance from a center observer, also on a train. The center observer will always view the two lightning strikes as simultaneous(granted he has no relative velocity from either lightning rod)

Anyways another observer is brought in to view the timing of the occurance. He is viewing from the ground, with a velocity relative to the lightning rods, since the train is moving. Given the constant velocity of light, from the viewpoint of the ground observer, he should view the light from the lightning rod closer to the front of the train as reaching the middle observer first. Or thats what most people would think, however thats not what happens. Because according to relativity of simultaineity, the ground observer views lightning strike, towards the rear of the train first. Then he sees the lightning strike the more forward rod next, just with the right difference of time delay to make the light reach the center observer at the exact same time, from any frame of reference. Simultaineity is based on velocity and the distance between objects. So all events not seperated by distance, are seen as simultaneous, and all events with no relative velocity to one another are also seen as simultaneous.

Now your thinking, what does that have to do with what I said? I said you have to view a photon, and you can only view a photon if it is traveling in your direction, so your question is meaningless. Well since events are always seen as simultaneous when there is no distance between them, you would never know which event happens, in what order. Given this logic, pretty much all of what einstein was saying is meaningless. The constant velocity of light, meaningless. Relativity of simultaneity, meaningless.

Just because something happens, not involving you doesn't mean it doesn't happen. There is plenty of light not traveling directly towards me, we are assuming I can view it with accuracy, just like Einstein does, just like many theorists do, about almost any theory. The question has arisen, this does happen. Either you know the answer or you dont. If you can answer it than do it.

#### ukmicky

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##### Re: lights velocity
« Reply #4 on: 15/07/2006 04:45:22 »
[:o)]

Michael

#### heikki

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##### Re: lights velocity
« Reply #5 on: 15/07/2006 12:08:48 »
quote:
Originally posted by thebrain13

Does light always have to move at c from you, even if its not traveling directly towards, or away from you? For example, if you drew a line from you, to a photon one light year away, and the photon was traveling perpendicular to the line. Would the photon be seen as traveling c from you, or at c from its starting point?

All things which have some kind of speed-motion has same properties of that point what you ask. It is the same properties even speed is very slow or high.

If thing speed is 1m/s and it goes away from you at speed 1m/s then it goes away that 1m/s.

I thing coming towards then it come that speed what is that speed.

Therefore if two things start to goes different direction and things (both) speed 1m/s then the separating speed 1m/s+1m/s=2m/s.

This mathematical law is equal all numeral speed values.

So simpple, dont need to make it much difficult, because it is not it.

Example.

When sun send things to space, direction east and west.

And if thing goes aways from sun at speed is xm/s,
then these things separating speed 2xm/s.

If x=300000km/s then 2x=600000km/s.

When sun send things-string ex.photons and things hit moon and reflect directly back then this things-strings meeting speed is 300000km/s+300000km/s=600000km/s. Theoretical only.

Nature that reflecting speed is lower because photon loose speed energy when hit moon so speed is little bit lower and speed is not 100% constant at this short time.

How long distance can one photon or lightpulse travell?

« Last Edit: 15/07/2006 12:10:02 by heikki »

#### another_someone

• Guest
##### Re: lights velocity
« Reply #6 on: 17/07/2006 01:10:21 »
quote:
Originally posted by thebrain13
Many of einsteins thought experiments, featured light that never hits you.

Personally, I am not even aware of one – would you care to find one that Einstein actually formulated?

quote:

Just because something happens, not involving you doesn't mean it doesn't happen. There is plenty of light not traveling directly towards me, we are assuming I can view it with accuracy, just like Einstein does, just like many theorists do, about almost any theory. The question has arisen, this does happen. Either you know the answer or you dont. If you can answer it than do it.

If you do not receive information about something, then it implies that for all practical purposes, it has not happened.  That having been said, the way the thing that happens involves you may be indirect (i.e. you see its effects, rather than see the thing itself).

With regard to the original question, you cannot see light that is not travelling towards you, but there are times when you can infer its existence by the effect it has on other objects that you can see.  In that respect, light must travel between the object (in the direction from one object to another) at exactly C (if it is travelling through a vacuum), but clearly, the speed at which it moves towards or away from you might be less than C.

For instance, if three people are stationed at the apex of an equilateral  triangle whose side is two light years in length, and if person A (at one apex) observes the experiment where person B (at the second apex) flashes a light simultaneously at person A and person C (where person C is at the third apex of the triangle), and person C flashes a light  to person A as soon as he sees the light flash from person B.  It is clear that person A cannot see the light travelling between person B and person C, but he can infer that the light has travelled between them, because person C has flashed his light to acknowledge having received the light from person B.  In such an experiment, since person B and person C are equidistant from person A, the light travelling between them has neither got closer to nor further away from person A at the end of its journey than the start – thus one may infer that its approach velocity towards person A is actually absolutely zero.

George
« Last Edit: 17/07/2006 01:22:30 by another_someone »

#### thebrain13

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##### Re: lights velocity
« Reply #7 on: 17/07/2006 03:11:24 »
That thought experiment was einsteins, trains (he always uses trains) lightning rods and all. It was just in my words. And I guess consequently, my understanding.

Under the belief that you have to absorb a photon directly to see it, I showed that it is impossible to see relativity of simultaneity. The reason is that when two objects, in this case photons aren't seperated, they are always simultaneous. And if you the observer, have to view two photons, then they are no longer seperated, so you cant view simultaneity. And if you cant view the velocity of c, what is the relevance of the constancy of the speed of light?

Now, I believe you established that in fact light can move under c, when it isn't moving directly towards or away from you. More precisely you could say if light isn't moving directly toward or away from you, it is always seen as moving under c. Relative to your position that is. This would have to be so, otherwise we would measure large assymetries between lights motion, for example it would be possible to see light move through a galaxy in less than a second, even in vacuo.

So relative velocity is kind of a misnomer. Laws are not based on the velocity relative to you, with the exception that an object is moving exactly towards or away from you. But relative velocity would have to be based upon its motion relative to where it was. In other words Relative velocity isn't relative to you.

#### jaybee

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##### Re: lights velocity
« Reply #8 on: 25/07/2006 04:00:43 »
heikki,

From Wipekedia: newbielink:http://en.wikipedia.org/wiki/Special_relativity [nonactive]

"Composition of velocities - velocities (and speeds) do not simply 'add'"

#### thebrain13

• Sr. Member
• Posts: 442
##### Re: lights velocity
« Reply #9 on: 26/07/2006 05:03:25 »
Since you no longer view light to be constant if it is not moving directly toward or away from you, how is non c moving light, affected by your relative motion?

How fast would you view light in this case. Lets say you were traveling at .99c relative to a starting point, a flash of light starts from the same starting point perpendicular to your motion at the same time, how fast do you see the light traveling relative to you, and how fast do you see it traveling relative to the starting point?

Now what if you were traveling at .1c?

#### ukmicky

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##### Re: lights velocity
« Reply #10 on: 26/07/2006 22:46:48 »
The speed of light is constant,the direction of view or the motion of the observer doesnt affect the speed that the observer measures light to be travelling at.
No matter how fast your moving light will always pass you by 186,000 miles per second faster than you.

Michael

#### thebrain13

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• Posts: 442
##### Re: lights velocity
« Reply #11 on: 27/07/2006 01:19:11 »
I am not talking about light traveling in the same direction as you. I know that light will always pass you at c. However light isn't going to be passing by anything in my example, its traveling perpendicular to you.

My question is what is the speed of light relative to, not when its traveling directly towards or away from you? And before you answer YOU, read the rest of my post.

And lastly you didn't answer what would happen in my experiment. So what would happen, based on what you just said?

#### ukmicky

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##### Re: lights velocity
« Reply #12 on: 27/07/2006 01:58:32 »
quote:
More precisely you could say if light isn't moving directly toward or away from you, it is always seen as moving under c.
No. How do you see it doing anything if its not traveling towards you . if you see it because it strikes something like the contents of a galaxy then your viewing a doppler shifted image of the things the photons hit.

quote:
Originally posted by thebrain13

Quote
I am not talking about light traveling in the same direction as you. I know that light will always pass you at c. However light isn't going to be passing by anything in my example, its traveling perpendicular to you.

once again  for you to see light  in a vacuum, for it to  be viewed and measured  its has got to be traveling towards you and therefore passing you.

Michael
« Last Edit: 27/07/2006 02:45:26 by ukmicky »

#### another_someone

• Guest
##### Re: lights velocity
« Reply #13 on: 27/07/2006 02:01:53 »
quote:
Originally posted by thebrain13

Since you no longer view light to be constant if it is not moving directly toward or away from you, how is non c moving light, affected by your relative motion?

How fast would you view light in this case. Lets say you were traveling at .99c relative to a starting point, a flash of light starts from the same starting point perpendicular to your motion at the same time, how fast do you see the light traveling relative to you, and how fast do you see it traveling relative to the starting point?

Now what if you were traveling at .1c?

The problem is that if light is not travelling towards you, you will not see the light, and you will have to infer its presence and speed by indirect means.  If you could clearly construct the complete thought experiment whereby you describe not only what you think the light will be doing, but how you think you would gain information about what it is doing, and then we can look at the total experiment and see what information it will tell us.

George

#### thebrain13

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• Posts: 442
##### Re: lights velocity
« Reply #14 on: 27/07/2006 02:44:35 »
The beam of light hits particle of dust the whole time its traveling, then it bounces and hits the observer. So it affects the object directly, there you happy? I believe it is completely unnecessary to include that, einstein never had to, and its very silly to imply that if something doesnt directly affect you then it doesnt happen.

#### thebrain13

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• Posts: 442
##### Re: lights velocity
« Reply #15 on: 27/07/2006 02:54:15 »
ukmikey redshifting wont change its velocity. So how does bouncing off something change the experiment?

#### ukmicky

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##### Re: lights velocity
« Reply #16 on: 27/07/2006 03:06:19 »
quote:
Originally posted by thebrain13

ukmikey redshifting wont change its velocity. So how does bouncing off something change the experiment?

quote:
The velocity of an object is simply its speed in a particular direction. Since velocity is defined as a vector, both speed and direction are required to define it.
http://en.wikipedia.org/wiki/Velocity

What happens to somethings velocity when it bounces and changes direction. What does velocity mean.?

.
Michael
« Last Edit: 27/07/2006 03:33:50 by ukmicky »

#### thebrain13

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##### Re: lights velocity
« Reply #17 on: 27/07/2006 03:34:15 »
what does that have to do with anything?

#### heikki

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##### Re: lights velocity
« Reply #18 on: 29/07/2006 16:39:41 »
quote:
Originally posted by jaybee

heikki,

"Composition of velocities - velocities (and speeds) do not simply 'add'"

Speed mathematical unit is m/s.

Where m is measured distance dimension.

S is time-unit.

When time unit is 1s it is 1s it cannot be anything else.

And if some object,

small or big,

goes some distance x at time 1s,

then speed is x/s.

If x is 500000km/1s then speed is 500000km/s.

If two objects goes same speed at different direction at speed x/s then that separate speed is 2x/s.

So, if these object speed is 500000km/s.

Then separate speed is 2*500000km=1000000km/s.

I cannot use other mathematical detour rules because mathematical rules are simple and scientifical proved.

My thought is that if we thing things what nature has, even parcicle motion or matter-vibrate motion, the both has same nature-laws and these nature-laws dont has constant-speed element. Of cource many things can says it is constant because changes happend so long time or distance that it is not important to known other and ofcource sometimes it is simply to use and compromise constant-value to made things understable and useful us.

#### another_someone

• Guest
##### Re: lights velocity
« Reply #19 on: 29/07/2006 16:56:28 »
quote:
Originally posted by heikki
Speed mathematical unit is m/s.

Where m is measured distance dimension.

S is time-unit.

When time unit is 1s it is 1s it cannot be anything else.

But this is the whole essence of relativity – what may appear as 1 second to you, may appear as 10 seconds to someone else, or 0.1 second to another person (all assuming they are in different inertial reference frames).  Likewise, what may appear as 1 metre to you, may be 10 meters to someone else, and 0.1 meters to another.

George

#### heikki

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##### Re: lights velocity
« Reply #20 on: 30/07/2006 07:33:32 »
quote:
Originally posted by another_someone

quote:
Originally posted by heikki
Speed mathematical unit is m/s.

Where m is measured distance dimension.

S is time-unit.

When time unit is 1s it is 1s it cannot be anything else.

But this is the whole essence of relativity – what may appear as 1 second to you, may appear as 10 seconds to someone else, or 0.1 second to another person (all assuming they are in different inertial reference frames).  Likewise, what may appear as 1 metre to you, may be 10 meters to someone else, and 0.1 meters to another.

George

Hi, A_s.

I havent read that mentioned theory of relativity and your wrotes is kind strange for me. When time-meauring unit is 1s it is 1s at all points, everywhere.

But, now i must says goodbay at this forum. It seems that you and other else who speak this forum, have read some theoryes and scient-books and then my thoughts are not same-kind than these books are, so then happend un-necessary different understanding.

I hope you nice life forward.

br. Heikki.

#### ukmicky

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##### Re: lights velocity
« Reply #21 on: 30/07/2006 16:41:12 »
heikki
If you would like to read Albert Einsteins special and general theorys of relativity you can down download it from here.

http://www.gutenberg.org/etext/5001

Michael
« Last Edit: 30/07/2006 16:50:29 by ukmicky »

#### another_someone

• Guest
##### Re: lights velocity
« Reply #22 on: 30/07/2006 23:27:42 »
quote:
Originally posted by heikki

Hi, A_s.

I havent read that mentioned theory of relativity and your wrotes is kind strange for me. When time-meauring unit is 1s it is 1s at all points, everywhere.

But, now i must says goodbay at this forum. It seems that you and other else who speak this forum, have read some theoryes and scient-books and then my thoughts are not same-kind than these books are, so then happend un-necessary different understanding.

I hope you nice life forward.

heikki,

Please do not leave simply because there are some things some of us have read that you have not.  The whole point about this forum is to spread the knowledge of science, and if every time someone comes across a theory they have not heard of being mentioned here they depart, it would leave this place fairly empty.

If you have questions – them please ask them.  If there are gaps in your knowledge (and believe me, there are very many gaps in my knowledge, as there is for all of us), then stick around and let us help you fill them.

Over the 9 or 10 months I have been here, I have had many of the gaps in my knowledge filled, and still continue to learn.

George

#### Solvay_1927

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##### Re: lights velocity
« Reply #23 on: 31/07/2006 02:43:26 »
I hope Heikki does come back.

Anyway, if you want a straight answer to your original question, Brain, it's:

The photon would be traveling at c from its starting point.

So if points A & B are 300,000 km apart, then a light ray would take 1 sec to travel from A to B.  And if you're at a point which is perpendicular to the line AB - let's say A is 300000km "west" of B, and you are 300000km "north" of B, then:
The light deflected off dust particles just after leaving A would take 1.4 sec to reach you (i.e. sqrt(2) - use Pythagoras' Theorem) - i.e. you'd see this light at t=1.4 sec;
And the light deflected off dust particles as it arrives at B would take 1 sec to reach you - i.e. you'd see this light at t=2 sec (where t=0 is the time when the light first leaves A).

So it would "appear" to you that the light beam has only taken 0.6 sec to go from A to B, but once you allow for the distances/geometry involved, you'd be able to work backwards to tell that the light beam actually took 1 sec to go from A to B.

#### thebrain13

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##### Re: lights velocity
« Reply #24 on: 26/07/2006 05:03:25 »
Since you no longer view light to be constant if it is not moving directly toward or away from you, how is non c moving light, affected by your relative motion?

How fast would you view light in this case. Lets say you were traveling at .99c relative to a starting point, a flash of light starts from the same starting point perpendicular to your motion at the same time, how fast do you see the light traveling relative to you, and how fast do you see it traveling relative to the starting point?

Now what if you were traveling at .1c?

#### The Naked Scientists Forum

##### Re: lights velocity
« Reply #24 on: 26/07/2006 05:03:25 »