Light speed is not constant or accurate

[Eric Ward]

Hi all, this my first forum ever. I'm a self taught physicist. So pardon my ignorance. I pose this question. If speed :s = distance :d ÷ by time :t Then how can we possibly measure our cosmos accurately with a measure of speed aka "Light Speed". The problem I see with this is TIME is a variable is the speed equation that changes throughout the cosmos/space-time. For example. Time Dilation. Since we know that gravity effects light. As it pulls light into a black hole. If light were to move past a large object, let's say a star. Then gravitational time dilation would speed light up as it left the stars gravity as observed from the star. "Relative velocity time dilation" would also slows down light as it speeds past an observer. Now multiply that by the light traveling across billions of objects like stars, planets, black holes even by galaxies over millions of years. How accurate can our "light speed measuring stick" possibly be at that point. This also raises another question. If we want to go faster than light we must first understand what the actual speed is in a control with all gravity taken out of that equation. It also may be lights Achilles heel. A way for us to beat it. I obviously understand that we are susceptible to time dilation too so the whole faster than light debate will be for another day. Today I pose this question and a statement, if the fastest thing in the universe is not as fast as we think it is or even faster and we use it to measure the cosmos, our entire understanding of the size our universe will grow or shrink with it.

 

[nikkkom]

As a start, have you read some introductory explanations such as

http://en.wikipedia.org/wiki/Speed_of_light ?

If no: please read it.

If you read it, please specify which specific part you don't understand or disagree with?

 

[Eric Ward]

Thank you for your reply Nikkkom, I have read the wiki "speed of light" link. I'm disputing the "time" part of the equation. Light speed was calculated with time. Since time is malleable. It isn't constant. It speeds up and slows down per Time Dilation since it is a particle and a wave. So the distance it covers in a said time will be different if it gets close to a mass it should slow down as it moves past. Then as it moves from the center of gravity of the mass It will speed up relative to the observer on the mass. If light is susceptible to "time dilation". It's speed is not constant to an observer. Below is the wiki link to "time dilation" a proven theory NASA deals with every day.
http://en.m.wikipedia.org/wiki/Time_dilation

 

[Ophiolite]

Eric, the central point is that the speed of light is constant. This has been very thoroughly validated. (Obviously we are talking about its speed in a vacuum.) Time dilation is something that effects the observer, not the light. Time dilation occurs because the speed of light is constant.

There are others here who can likely explain this much clearer than I can, should your doubts remain.

 

[ZapperZ]

Thank you for your reply Nikkkom, I have read the wiki "speed of light" link. I'm disputing the "time" part of the equation. Light speed was calculated with time. Since time is malleable. It isn't constant. It speeds up and slows down per Time Dilation since it is a particle and a wave. So the distance it covers in a said time will be different if it gets close to a mass it should slow down as it moves past. Then as it moves from the center of gravity of the mass It will speed up relative to the observer on the mass. If light is susceptible to "time dilation". It's speed is not constant to an observer. Below is the wiki link to "time dilation" a proven theory NASA deals with every day.
http://en.m.wikipedia.org/wiki/Time_dilation

This is awfully silly.

The phenomenon of "time dilation" is a DIRECT CONSEQUENCE of the postulates of Special Relativity, which explicitly includes Lorentz invariance, and the constancy of the speed of light. Somehow, you then turn around and use that consequence to show that speed of light is not a constant since time is "malleable"? You used something, which actually depended on c being a constant, to show that it isn't a constant? If c isn't a constant, you cannot use "time dilation", because it won't be correct either!

If c isn't a constant in all reference frame, your GPS will be horribly inaccurate!

There is a serious misunderstanding of SR here, and a very large hole in logic.

Zz.

 

[Eric Ward]

Consider me enlightened! Thank you for your replies. Thank you for putting up with my ignorance. So your saying light is constant because the principals of time dilation are founded on light is a constant. Would that mean that both ideas are not accurate if they consider light as a constant. Keep in mind when we first measured light it was done on Earth in Earth's gravity. This should cause the speed to appear to be slower than it actually is to us the observers on earth. Or are you suggesting that a light is unaffected by gravity or time dilation? That's a real question. I really don't know. Thank you again. E

 

[jbriggs444]

To be fair to OP, if it were true that the conclusion that "time is malleable" followed from the premise that the speed of light is constant and if it were also true that the speed of light is inconstant followed from the premise that "time is malleable" then one would have a proof by contradiction showing that the speed of light is inconstant.

In fact, however, the argument fails because "time is malleable" is a hand wave rather than something that SR actually says.

 

[jbriggs444]

Keep in mind when we first measured light it was done on Earth in Earth's gravity. This should cause the speed to appear to be slower than it actually is to us the observers on earth. Or are you suggesting that a light is unaffected by gravity or time dilation?

The speed of light measured locally is always c. Gravity neither speeds it up nor slows it down. [Nor even changes its direction. It is space-time itself that is curved. Light goes "straight" within curved space-time].

Time dilation, length contraction and the relativity of simultaneity conspire so that the speed of light is always measured to be the same regardless of your choice of inertial reference frame.

 

[Mentz114]

Consider me enlightened! Thank you for your replies. Thank you for putting up with my ignorance. So your saying light is constant because the principals of time dilation are founded on light is a constant. Would that mean that both ideas are not accurate if they consider light as a constant. Keep in mind when we first measured light it was done on Earth in Earth's gravity. This should cause the speed to appear to be slower than it actually is to us the observers on earth. Or are you suggesting that a light is unaffected by gravity or time dilation? That's a real question. I really don't know. Thank you again. E

If you measure the velocity of something in your lab - then that is the speed it is travelling. What does 'actually is' mean in the bolded part ?

 

[mfb]

I think you are looking for Shapiro delay: the time light needs to reach us from a planet behind the sun is a bit longer than it would be without the sun in between, for example. This effect is well-known, but it is negligible if we look at random astronomical objects - massive objects like our sun are incredibly rare, and we cannot measure distances of billions of light years better than a few percent anyway so a few years do not make a difference.

Another interesting case arises from different distances if light is curved due to nearby masses (gravitational lensing). This can lead to multiple images of the same object, including a time delay between those images. 14 months for the Twin Quasar, for example: whatever we see in the first image will be visible in the second image 14 months later.

The title was not a good choice.

 

[Eric Ward]

If you measure the velocity of something in your lab - then that is the speed it is travelling. What does 'actually is' mean in the bolded part ?

"Actually is" means the speed light is traveling if it was being observed with no gravitational time dilation affecting it's observed speed. In a lab on Earth or even in lower orbit it would be subject to gravitational time dilation. It would have to be observed away from all gravity to be as accurate. Which would be impossible because there will always be some type of micro gravity in space from something. Of course this is. This is all assuming the light is affected by gravity.

 

[Eric Ward]

I think you are looking for Shapiro delay: the time light needs to reach us from a planet behind the sun is a bit longer than it would be without the sun in between, for example. This effect is well-known, but it is negligible if we look at random astronomical objects - massive objects like our sun are incredibly rare, and we cannot measure distances of billions of light years better than a few percent anyway so a few years do not make a difference.

Another interesting case arises from different distances if light is curved due to nearby masses (gravitational lensing). This can lead to multiple images of the same object, including a time delay between those images. 14 months for the Twin Quasar, for example: whatever we see in the first image will be visible in the second image 14 months later.

The title was not a good choice.

The title was on purpose. I wanted to get a larger group of people to view it. And get what you finally gave me. I'm familiar with lensing but I'm not with Shapiro Delay. If off to study that till the wee hours of the morning. Thank you! E

 

[Eric Ward]

Copied from wiki on "Shapiro Delay". Thank you MFB. Wish I would have thought of it first.

Because, according to the general theory, the speed of a light wave depends on the strength of the gravitational potential along its path, these time delays should thereby be increased by almost 2x10−4 sec when the radar pulses pass near the sun. Such a change, equivalent to 60 km in distance, could now be measured over the required path length to within about 5 to 10% with presently obtainable equipment.

Calculating time delay..

In a near-static gravitational field of moderate strength (say, of stars and planets, but not one of a black hole or close binary system of neutron stars) the effect may be considered as a special case of gravitational time dilation.The measured elapsed time of a light signal in a gravitational field is longer than it would be without the field, and for moderate strength near-static fields the difference is directly proportional to the classical gravitational potential, precisely as given by standard gravitational time dilation formulas.

 

[ZapperZ]

I wish mfb didn't introduce this, because I can easily see how someone like you can completely misinterpret and misread such a thing as evidence that light changes its speed in such cases. This is where a little knowledge can lead to a wildly wrong idea!

The problem here is that you are trying to run when you can't even crawl. GR is extremely difficult to understand and the mathematics is daunting. SR is, actually, a much simpler idea with surprisingly simple mathematics! That is what you need to learn and understand FIRST! Diving into GR like this is like teaching a toddler how to climb a tree when he hasn't even learned how to stand up straight!

And no, as was mentioned, this was NOT a very good topic, regardless of your intention. There are better ways to get attention than throwing out a standard crackpottish title like this. Warren Siegel even included an entry in the same vein with regards to quacks. But besides that, there is a certain level of incredible disrespect here. One would think that with a lot of very intelligent physicists around, something as obvious as what you stated in the first post would have been caught already, if it were true! Seriously, how dumb do you think physicists are to not be able to see something that is right in their faces? But instead of taking a diplomatic approach and to first figure out if you had actually understood what you think you understood, you jumped right with such a proclamation that light speed is not accurate or constant!

There are tactful way to learn, if that is the intention. You don't insult the people that you wish to learn from.

Zz.

 

[Eric Ward]

I wish mfb didn't introduce this, because I can easily see how someone like you can completely misinterpret and misread such a thing as evidence that light changes its speed in such cases. This is where a little knowledge can lead to a wildly wrong idea!

The problem here is that you are trying to run when you can't even crawl. GR is extremely difficult to understand and the mathematics is daunting. SR is, actually, a much simpler idea with surprisingly simple mathematics! That is what you need to learn and understand FIRST!

And no, as was mentioned, this was NOT a very good topic, regardless of your intention. There are better ways to get attention than throwing out a standard crackpottish title like this. Warren Siegel even included an entry in the same vein with regards to quacks. But besides that, there is a certain level of incredible disrespect here. One would think that with a lot of very intelligent physicists around, something as obvious as what you stated in the first post would have been caught already, if it were true! Seriously, how dumb do you think physicists are to not be able to see something that is right in their faces? But instead of taking a diplomatic approach and to first figure out if you had actually understood what you think you understood, you jumped right with such a proclamation that light speed is not accurate or constant!

There are tactful way to learn, if that is the intention. You don't insult the people that you wish to learn from.

Zz.

My apologies Zapper Z. You teach me more than you know. I appreciate your disrespect. It is well deserved and does not offend me. I understand I am nothing, I can only hope one day to have the understanding that you've been afforded. I'm just a dumb human being on this planet curious about the world around me and hungry for answers. This was an attempt to understand if my idea had teeth and was at all relevant. I appreciate your reply and respect you immensely. Respectfully Eric

 

[Mentz114]

"Actually is" means the speed light is traveling if it was being observed with no gravitational time dilation affecting it's observed speed. In a lab on Earth or even in lower orbit it would be subject to gravitational time dilation. It would have to be observed away from all gravity to be as accurate. Which would be impossible because there will always be some type of micro gravity in space from something. Of course this is. This is all assuming the light is affected by gravity.

When we say 'the speed of light is a constant' it means that anyone measuring this speed gets the same answer. So if the observer on Earth did it, and another observer far away from matter did it - they both get 400.3462x10¹⁷ furlongs/fortnight, when they harmonise their units.

 

[PeterDonis]

"Actually is" means the speed light is traveling if it was being observed with no gravitational time dilation affecting it's observed speed.

There is no way to measure this. If your lab on Earth is in a gravitational field, then you can measure the speed light is traveling in your lab, in the gravitational field, but there is no way to measure what the speed in your lab would have been if the field were not there. Even if you put your lab in a rocket and travel out into deep space, far away from all gravitating bodies, and measure the speed of light in your lab there, that still doesn't tell you what the speed would have been in the lab back on Earth if the Earth's field were not there.

As Mentz114 said, "the speed of light is constant" means everyone that measures it gets the same answer, no matter where they are. Strictly speaking, we should say that everybody in a local inertial frame gets the same answer--i.e., strictly speaking, your lab should be in free fall--for example, do the measurement in orbit, say on the International Space Station.

 

[Eric Ward]

My apologies Zapper Z. You teach me more than you know. I appreciate your disrespect. It is well deserved and does not offend me. I understand I am nothing, I can only hope one day to have the understanding that you've been afforded. I'm just a dumb human being on this planet curious about the world around me and hungry for answers. This was an attempt to understand if my idea had teeth and was at all relevant. I appreciate your reply and respect you immensely. Respectfully Eric

Oh and I don't think that light slows down i

When we say 'the speed of light is a constant' it means that anyone measuring this speed gets the same answer. So if the observer on Earth did it, and another observer far away from matter did it - they both get 400.3462x10¹⁷ furlongs/fortnight, when they harmonise their units.

There is no way to measure this. If your lab on Earth is in a gravitational field, then you can measure the speed light is traveling in your lab, in the gravitational field, but there is no way to measure what the speed in your lab would have been if the field were not there. Even if you put your lab in a rocket and travel out into deep space, far away from all gravitating bodies, and measure the speed of light in your lab there, that still doesn't tell you what the speed would have been in the lab back on Earth if the Earth's field were not there.

As Mentz114 said, "the speed of light is constant" means everyone that measures it gets the same answer, no matter where they are. Strictly speaking, we should say that everybody in a local inertial frame gets the same answer--i.e., strictly speaking, your lab should be in free fall--for example, do the measurement in orbit, say on the International Space Station.

Thank you, Mentz114 and Peter Donis. Great answers. So I'm getting the answer that Light does not slow down or speed up when it encounters gravity. Per Time dilation. As observed by an observer not traveling with the light. Then why does time dilation not affect light? If light is both a particle and a wave? I understand how it's not affected as a wave but I don't understand why it does not affect a light particle. Especially since light is supposed to be trapped beyond he event horizon (or the new apparent horizon) in a black hole.

 

[Eric Ward]

Oh and I don't think that light slows down i
Thank you, Mentz114 and Peter Donis. Great answers. So I'm getting the answer that Light does not slow down or speed up when it encounters gravity. Per Time dilation. As observed by an observer not traveling with the light. Then why does time dilation not affect light? If light is both a particle and a wave? I understand how it's not affected as a wave but I don't understand why it does not affect a light particle. Especially since light is supposed to be trapped beyond he event horizon (or the new apparent horizon) in a black hole.

I'm speaking of course in the eyes of the observer.

 

[mfb]

If light is both a particle and a wave?

It shows properties of both, but it is neither.
Asking for time dilation does not make sense for objects at the speed of light.

 

[Eric Ward]

It shows properties of both, but it is neither.
Asking for time dilation does not make sense for objects at the speed of light.

Thank you mfb.

 

[phinds]

Then why does time dilation not affect light?

Time dilation doesn't affect anything. Time dilation is something observed by a remote observer. You, for example, right now as you are reading this are MASSIVELY time dilated according to an accelerated particle at CERN. Do you feel any effect?

 

[Zentrails]

Time dilation doesn't affect anything. Time dilation is something observed by a remote observer. You, for example, right now as you are reading this are MASSIVELY time dilated according to an accelerated particle at CERN. Do you feel any effect?

Great pun relativistically speaking, but just to make sure the OP doesn't get confused I think you meant a particle traveling close to the speed of light rather than accelerated.

 

[Eric Ward]

Time dilation doesn't affect anything. Time dilation is something observed by a remote observer. You, for example, right now as you are reading this are MASSIVELY time dilated according to an accelerated particle at CERN. Do you feel any effect?

No, but if the particle at CERN was timing how long it took me to blink an eye and used that to measure its universe it would experience a slowed down timing of my blink due to its high speed. ... I understand light speed is constant. I just want to know if we are observing the correct light speed on earth. Great analogy btw!

 

[phinds]

Great pun relativistically speaking, but just to make sure the OP doesn't get confused I think you meant a particle traveling close to the speed of light rather than accelerated.

Traveling close to the speed of light relative to what? I meant accelerated relative to the Earth, which seems fairly clear since I specified CERN, and yes, that is "traveling close to the speed of light" but specifically relative to the Earth.

EDIT: Also, how do you get "pun" out of this? I must be missing something, since I see nothing at all about it that seems like a pun.

 

[phinds]

Great analogy btw!

It is not an analogy, it is a direct statement of fact.

 

[Eric Ward]

No, but if the particle at CERN was timing how long it took me to blink an eye and used that to measure its universe it would experience a slowed down timing of my blink due to its high speed. ... I understand light speed is constant. I just want to know if we are observing the correct light speed on earth. Great analogy btw!

It is not an analogy, it is a direct statement of fact.

Agreed..

 

[Mentz114]

No, but if the particle at CERN was timing how long it took me to blink an eye and used that to measure its universe it would experience a slowed down timing of my blink due to its high speed. ... I understand light speed is constant. I just want to know if we are observing the correct light speed on earth. Great analogy btw!

That is not true. Time dilation is not directly observable. Your 'blink time' would be subject to the Doppler effect between labs that are in relative motion.

 

[Eric Ward]

You guys are great btw! Thank you for all of your awesome answers. I'm a huge science geek. I started with astronomy and meteorology in my 20s and moved to studying physics 3 years ago. I wish I could go to school and be full time. It would be just be irresponsible to go back to school with a wife and kids. So I'm stuck in my current career . But just know you guys are my heros!

 

[PeterDonis]

I just want to know if we are observing the correct light speed on earth.

I'm not sure what you mean by the "correct" light speed, but if you mean something like you said before, along the lines of "the speed we would measure if the Earth's gravitational field were not there", this is a meaningless concept, for reasons I explained in a previous post.

 

[Eric Ward]

That is not true. Time dilation is not directly observable. Your 'blink time' would be subject to the Doppler effect between labs that are in relative motion.

I've hear physicist say that if a rocket ship was shot into a black hole it would appear to slow down because of gravitational time dilation. I miss spoke about the particle observing a slower reality. It would experience

I'm not sure what you mean by the "correct" light speed, but if you mean something like you said before, along the lines of "the speed we would measure if the Earth's gravitational field were not there", this is a meaningless concept, for reasons I explained in a previous post.

You are correct. I accept this now and have a clearer understanding of SR surrounding time dilation. Thank you. E

 

[Mentz114]

I've hear physicist say that if a rocket ship was shot into a black hole it would appear to slow down because of gravitational time dilation. I miss spoke about the particle observing a slower reality. It would experience...

The problem here is that you are trying to run when you can't even crawl. GR is extremely difficult to understand and the mathematics is daunting. SR is, actually, a much simpler idea with surprisingly simple mathematics! That is what you need to learn and understand FIRST! Diving into GR like this is like teaching a toddler how to climb a tree when he hasn't even learned how to stand up straight! - ZapperZ

 

[Eric Ward]

The problem here is that you are trying to run when you can't even crawl. GR is extremely difficult to understand and the mathematics is daunting. SR is, actually, a much simpler idea with surprisingly simple mathematics! That is what you need to learn and understand FIRST! Diving into GR like this is like teaching a toddler how to climb a tree when he hasn't even learned how to stand up straight! - ZapperZ

Thank you. I didn't intend for that to post. It was incomplete. Zapper hit the nail on the head. E

 

[Dale]

Just as an aside. The meter used to be defined by a couple of marks on a metal bar. (Skipping a few steps) then we tried to measure the speed of light and found it to be so constant that most of the inaccuracy in the speed of light was due to inaccuracy in the meter. Now we can get incredibly precise and reproducible measures of the meter by defining the speed of light to gave a fixed constant.

 

[doaaron]

Regarding the whole point about the speed of light being constant, these scientist think that they have managed to slow down the speed of light.

http://www.bbc.com/news/uk-scotland-glasgow-west-30944584

Forgetting about whether their experimental setup was correct or not, I wonder what the experts think would be the implications wrt SR GR etc.Aaron