Can an imminent laser strike ever be observable?

[Hornbein]

not to try to answer my own queries but I think the answer under relativity is that I don’t have more time inside the ship, as a result of how fast or slow I may have propelled it relative to the laser. It’s tough to wrap my mind around that because an inch a day slower than C, or a micron a millennium slower than C, are both less than C, it means I’d see the laser pass me at C as if I am not moving relative to it, at all. For that matter I think if I were to pass it in the opposite direction a micron a year under C, same result. This really wasn’t the question I was wondering about originally but it (SR GR) has a certain way about it, of becoming the analysis.

A cartooned steam train with a lantern by a pedestrian with a lantern is sure easier for me to take at face value.

Your relative speed makes a difference. If you are moving away from the beam source then the laser will to you have less energy. If moving away at extreme speed the beam will have so little energy that you might not be able to detect it.

 

[hutchphd]

But the wavefront will still move at c relative to you. Eibnstein's seminal (boyhood!) thinking was in fact about watching a light beam while traveling along with it and rationalizing Maxwell to this process. He concluded some remarkable things which led him to the special theory. You do not seem to understand these precedents, and therefore connot get past this misunderstanding.

 

[davidjoe]

But the wavefront will still move at c relative to you. Eibnstein's seminal thinking was in fact about watching a light beam while traveling along with it and rationalizing Maxwell to this process. He concluded some remarkable things which led him to the special theory. You do not seem to understand these prrecedents, and therefore connot get past this misunderstanding.

That’s probably fair to say. I do understand that he decided it is correct that the constant is going to be the speed of light, as observed in all frames of reference, and that everything that must change to conform to that supposition, will be so changed to be relative, such as space, time and length. I do also understand that a Constant C, always observed as the same, if we tried to apply it to other speeds, doesn’t give us the same results. I would like to understand how that particular, exact speed triggers so many nonlinear results, compared to speeds slightly slower.

 

[Averagesupernova]

I'm certainly no expert on relativity but it seems pretty simple to me that you can't see a light beam coming. If one can wrap their head around not being able to hear a supersonic jet approach, then I can't understand why it's so difficult to realize that the laser announces its arrival upon its arrival.
-
If you have someone aim a laser as to intersect the position of the earth at some future date and turn the laser on ahead of time I suppose it is possible to detect it as dust and particles in space are illuminated. But if the laser is turned on at such time so that the beam arrives at the exact moment the earth arrives at the chosen position, the laser will announce its arrival at its arrival.

 

[davidjoe]

If one can wrap their head around not being able to hear a supersonic jet approach, then I can't understand why it's so difficult to realize that the laser announces its arrival upon its arrival.

Well, fair enough but no one asserts that no matter how fast a sub sonic jet travels, sound passes it at the speed of sound.

 

[davidjoe]

What would be hard to engage as a concept, and is for me, assuming AE didn’t explain it himself, and I have never heard that he did, is what is so different about - 1 Planck length per googleplex of time, that proportionality and linearity disappear. I understand the concept of 100%. There’s nothing possible, further. But 100% of anything, be it speed, time, matter, does not equal an infinity of that.

 

[davidjoe]

If we weren’t talking about a laser passing me, but a missile, and the delta in speed was that infinitesimally small amount, it’s one under C and and I’m two under it (smallest gradation units imaginable) no one would assert that the missile passes me at nearly light speed, we’d be talking eons of time beside each other.

 

[davidjoe]

Not saying it’s impossible, just wanting to know why.

 

[Vanadium 50]

Because the laser takes the shortest path and nothing travels faster than light.

 

[sbrothy]

If you are in line with it, arrival is without notice, but what if it were fired to intersect with the point where earth “will be” say from the second closest star, several light years away, and during that period of travel, the bodies get further apart, in non parallel paths.

Is it possible to see it fired, not directly at you, then a few minutes or hours later, be hit by it, and what would you see if you trained the telescope on that beam from when you saw it fired, to impact?

It's like that "famous" quote from Star Trek:

"Object nearing at light speed captain, no visual contact yet."

 

[hutchphd]

Which is the triangle inequality.

Not saying it’s impossible, just wanting to know why.

The fact that light travels travels the same speed independent of source follows from Maxwell and no explicit frame dependence therein. Many possibilities were considered to save "common sense" but the universe refused to cooperate. Einstein's relentlessly uniform interpretation leads to many testable consequences and has never been shown incorrect. Answering the "why" question requires a higher pay grade than you will find here. Ask Mr. Trump.....

 

[davidjoe]

Which is the triangle inequality.


The fact that light travels travels the same speed independent of source follows from Maxwell and no explicit frame dependence therein. Many possibilities were considered to save "common sense" but the universe refused to cooperate.

That light does not go faster when emitted from a moving platform is not troublesome to me. Sound waves also do not exceed the speed of sound, when propagating from a moving car.

What strains my brain, is that light passing me from an independent source, when we are traveling at the smallest difference in speed, will pass me at light speed, as if I’m not moving at all. This is especially troublesome, because if that special speed is reduced by the slightest amount, everything changes. Now it passes me according to classical physics motion analysis, meaning it barely passes me whatsoever.

As to traveling alongside light, he did analyze that. But as I understand our view of relativity, no, there is no such thing. A photon, all of them, will stream by you at light speed, irrespective of however close your speed is, which can never reach C, and so you will never see them unless there is contact. This being all based on relativity, seems to call into question what theoretical or actual observations there could possibly be made, about light and motion, if traveling alongside a photon can’t happen, and the closest we have to that, is the same effect as being stationary when light streams by.

 

[Vanadium 50]

That light does not go faster when emitted from a moving platform is not troublesome to me.

So...what do you want us to do about that? That's been measured to be true. (And how is this science fiction?)

 

[Janus]

What strains my brain, is that light passing me from an independent source, when we are traveling at the smallest difference in speed, will pass me at light speed, as if I’m not moving at all. This is especially troublesome, because if that special speed is reduced by the slightest amount, everything changes. Now it passes me according to classical physics motion analysis, meaning it barely passes me whatsoever.

No, everything doesn't change. Everything, regardless of how fast it moves are subject to Relativity. For example, in Newtonian Physics, you add velocities by V1+V2= VT, but in Relativity, it is (V1+V2)/(1+V1(V2)/c^2)
If V1 is 0.001c and V2is 0.001c, then Newton says they add to 0.002 c, but Relativity says they add to 0.001999998... c. The effects are still there. they just become less noticeable at speeds significantly less than c.

 

[davidjoe]

So...what do you want us to do about that? That's been measured to be true. (And how is this science fiction?)

It’s not science fiction. I was replying to another’s statement. I would imagine that it is measured true, and I’m suggesting sound also does exactly that.

The only theory that would suggest it is not true, is slippage in one’s thinking, along the lines that if light is not subject to platforms or frames varying its perceived speed, then they are incapable of affecting its constancy, which they do, evidently as light propagating from a locomotive or a pedestrian both reach an equidistant point at the same time.

 

[davidjoe]

No, everything doesn't change. Everything, regardless of how fast it moves are subject to Relativity. For example, in Newtonian Physics, you add velocities by V1+V2= VT, but in Relativity, it is (V1+V2)/(1+V1(V2)/c^2)
If V1 is 0.001c and V2is 0.001c, then Newton says they add to 0.002 c, but Relativity says they add to 0.001999998... c. The effects are still there. they just become less noticeable at speeds significantly less than c.

That’s new and different, then, from the thinking here, - that if I’m going C minus “1 iota”, a laser streams past me, at difference between no velocity, and C.

 

[DaveC426913]

That light does not go faster when emitted from a moving platform is not troublesome to me. Sound waves also do not exceed the speed of sound, when propagating from a moving car.

What strains my brain, is that light passing me from an independent source, when we are traveling at the smallest difference in speed, will pass me at light speed, as if I’m not moving at all. This is especially troublesome, because if that special speed is reduced by the slightest amount, everything changes. Now it passes me according to classical physics motion analysis, meaning it barely passes me whatsoever.

This is simply not true.

No matter what speed you are doing* - be it 0 or .9999c or anything in between, light will propagate at c.

* note that "speed" is relative to some physical reference point - a planet, a star, a galaxy, whatever. And it's arbitrary which one you pick. You are always at rest in your own reference frame and it is the planets and stars that are moving. And in your own reference frame, light always moves at c.

 

[davidjoe]

Well, I must have misunderstood. I thought it has been said I will observe light pass me at a difference of C, “because all frames observe the speed of light as the same”. I took this to mean that if I’m stationary, it passes at C. If I’m one iota slower than light, at the same spot when it passes, that’s a reference frame, and therefore I see it pass at C. Or I don’t see it, rather, but that’s what happens.

See post 37 and there about.

 

[davidjoe]

Post 37 and circa…. I read those to say it passes me as if I’m not moving, as I see it from my frame.

It’s one, or the other. I think both possibilities have been elaborated upon as the result. Possibly a reply to the others besides mine, would be in order.

 

[davidjoe]

Let’s try to clear this up. If I am going one iota under light speed, and a laser beam approaches me on a virtually parallel path that is a few feet to my right, does it, as I see it:

A) pass by me at the “difference” of the speed of light; or,

B) creep up to, beside, and go in front of me, spread out over many lifetimes, because there is almost no difference in our speeds?

This is the pressure point. Where classical and relative part ways: only the speed of light is deemed the same from all reference frames. So, one of these can’t be right, I believe. I don’t know myself, only curious.

 

[sophiecentaur]

B) creep up to, beside, and go in front of me, spread out over many lifetimes, because there is almost no difference in our speeds?

It will go past you at c but the frequency will be (red) shifted, possibly by so much that it will be beyond the visible red part of the spectrum. (Like the light that arrives from the most distant receding galaxies)

"creep up" is not the right way to say it because it is still at c, relative to yo.

 

[davidjoe]

It will go past you at c but the frequency will be (red) shifted, possibly by so much that it will be beyond the visible red part of the spectrum. (Like the light that arrives from the most distant receding galaxies)

"creep up" is not the right way to say it because it is still at c, relative to yo.

Light goes by everything, whether moving or not, at C. Light is always going C, right, so that is a given; it’s the difference in perceived speeds that is the question.

It’s a very granular, specific hypothetical sub question, not meant to put anybody on the spot. Do my senses, biological and/or mechanical contained in my near-C vessel, perceive it pass by me in fractions of microseconds, or thousands of years, given that my speed is virtually the same but infinitesimally less than C?

It’s really got to be an A or B, or neither type answer, right? If light is gaining on me from a lead of a second, at an inch a day’s difference in speed, creeping up is a good word choice.

 

[sophiecentaur]

it’s the difference in perceived speeds that is the question.

No it's not. The perceived speed to the fast moving observer is c - always. As I mentioned, for consistency, the perceived wavelength is shifted.

It’s really got to be an A or B

Only in your world. You need to adjust your model if you want to understand this; you can't force reality to fit your ideas, I'm afraid.

 

[davidjoe]

No it's not. The perceived speed to the fast moving observer is c - always. As I mentioned, for consistency, the perceived wavelength is shifted.

Only in your world. You need to adjust your model if you want to understand this; you can't force reality to fit your ideas, I'm afraid.

So, A, the laser is perceived to pass the ship at light speed, and the ship’s speed marginally under C, does not matter. The ship being passed by the laser, observing it and only it, could not discern any difference between standing still or almost traveling at C.

If the laser was any object infinitesimally slower than C, the hard and fast observation of it traveling at C does not apply, and I believe I would observe it for a great length of time, or B, because our speeds are nearly identical.

Am I wrong about ONLY light speed being observed as a constant from all reference frames? This does not apply to any lesser speeds, right, it’s a bright line distinction?

How can the options of “A or B or neither” be objectionable? How can “neither” be left out of the quote box? It’s like ending the quote as “It’s got to be A”.

 

[hutchphd]

we are traveling at the smallest difference in speed

light passing me from an independent source, when we are traveling at the smallest difference in speed, will pass me at light speed, as if I’m not moving at all. This is especially troublesome, because if that special speed is reduced by the slightest amount, everything changes.

Light does not allowed to reduce its speed by the smallest amount.....nor can you actually reach the speed c. The physics falls apart. So not a problem: it doesn't happen

As to traveling alongside light, he did analyze that. But as I understand our view of relativity, no, there is no such thing

He pointed out the problem.

if light is not subject to platforms or frames varying its perceived speed, then they are incapable of affecting its constancy, which they do, evidently as light propagating from a locomotive or a pedestrian both reach an equidistant point at the same time.

Why would light care what a locomotive or pedestrian are doing? It is just being light.

That’s new and different, then, from the thinking here,

No. Your perception of how velocities in moving frames of reference actually add is incorrect. (V1+V2)/(1+V1(V2)/c^2)

How can the options of A or B or neither, be objectionable? How can “neither” be left out of the quote box? It’s like ending the quote as “It’s got to be A”.

I think this is not logical, although I am unsure the question you are asking.

 

[davidjoe]

I’m playing by the rules, Hutch. I’m not suggesting an object reach or exceed light speed.

I’m simply examining the constituent components of relativity.

Relativity does not require suspension of any logical precepts, to my knowledge.

Without reaching the speed of light, by only the slimmest of margins, your speed of C minus one iota, is NOT a constant in all reference frames, and has more in common with .00011 mm per year, than it does with C, right, with respect to how your speed is perceived by others.

This shouldn’t be an avoided question to my thinking, right, relativity is a theory, not a person being examined on a table.

 

[DaveC426913]

Well, I must have misunderstood. I thought it has been said I will observe light pass me at a difference of C, “because all frames observe the speed of light as the same”.

Correct.

I took this to mean that if I’m stationary, it passes at C.

Correct.

If I’m one iota slower than light, at the same spot when it passes, that’s a reference frame, and therefore I see it pass at C.

Correct.

But then you said this:

if that special speed is reduced by the slightest amount, everything changes. Now it passes me according to classical physics motion analysis, meaning it barely passes me whatsoever.

Which is incorrect.

 

[DaveC426913]

... relativity is a theory, not a person being examined on a table.

The theory part is Einstein's curved space-time - a model of how light behaves the way we see it behave. But the observations are incontrovertible.

No matter what your frame of reference - whether you are moving or stationary, relative to some planet or star or galaxy, you will always observe the speed of light (in a vacuum) to be c.

Any theory that wishes to explain light must address that fact.

There are reasons for why it may not make sense at first, but it requires going down the rabbit hole of relativity. I'm not sure you are ready to make that journey yet. It requires throwing away your classical preconceptions and not drawing hasty conclusions from what you have learned about the classical world - which is kind of what you are doing now.

It's sort of beyond a single forum thread. The best way would be to pick up a basic primer book on relativity.

 

[hutchphd]

Without reaching the speed of light, by only the slimmest of margins, your speed of C minus one iota, is NOT a constant in all reference frames, and has more in common with .00011 mm per year, than it does with C, right, with respect to how your speed is perceived by others.

This shouldn’t be an avoided question to my thinking, right, relativity is a theory, not a person being examined on a table.

With respect. I have no desire to examine theory of relativity: I have made my peace with the intuitively difficult parts long ago, and recapitulating the tenets will likely not be useful to you. In fact what is subject to examination is your inability to understand the theory because of prejudices you do not seem to realize that you have. These are what is on the table. It requires you to ask specific guestions about the theory; not complain about our answers. Hopefully something will click and illumination will result. Or perhaps not. Your questions are not trivial or foolish but you need to be open to the very good answers being supplied to you. And please make your questions about theory and not epistomology

 

[Janus]

That’s new and different, then, from the thinking here, - that if I’m going C minus “1 iota”, a laser streams past me, at difference between no velocity, and C.

You are moving at say 0.9999c relative to laser emitter. To find the speed the light moves relative to you, As measured by you, Newtonian physics says you use 1c-0.9999c = 0.0001c.
With Relativity, you use (1c-0.9999c)/(1- 1c(0.9999c)/c^2. A bit of simplifying yields (1c-0.9999c)/(1-0.9999c^2/c^2) = (1c-0.9999c)/(1-0.9999) = c(1-0.9999)/(1-0.9999) = c. as long as the magnitude of one of the velocities you are working with is c, you get an answer of c.

 

[sophiecentaur]

The theory part is Einstein's curved space-time

That introduces GR. It is not part of the OP's question, which is just about Special Relativity. I think that one step at a time is appropriate here.

The OP's problem seems to be that he wants to introduce some particular speed which is a barrier between one set of observations and another. The fact is that Special Relativity operates, whatever speed you are going at; it's just that the effects are very small at speeds which are achievable by an observer.

I have made the point twice (and he doesn't seem to have picked up on it) that is there are other effects / consequences of the invariable speed of light. Apparent distances, apparent times and apparent frequencies change at (mostly) high relative speeds so the OP's problem of light suddenly behaving differently is irrelevant; Nothing is fixed apart from the speed of light; the rest of Physics fits itself around that. AND our personal views or mental models have to fit in with it too. There's no way out of that.

Relativity does not require suspension of any logical precepts, to my knowledge.

It certainly required suspension of the views of many very clever people in the early twentieth century. You, also, may need to re-examine what you mean by your 'logical precepts'. They are preconceptions and not necessarily logical; they do not fit with measurements, for a start.

 

[davidjoe]

New address for the thread SR. I still pose this sub question:

“If the speed of light is reduced by the slightest amount, (in the form of a fast object), is it observed to be constant, from all reference frames?”

My understanding is that this distinction applies to only light speed. It IS is a bright line difference.

 

[sophiecentaur]

New address for the thread SR. I still pose this sub question:

“If the speed of light is reduced by the slightest amount, (in the form of a fast object), is it observed to be Constant, from all reference frames?”

My understanding is that this distinction applies to only light speed. It IS is a bright line difference.

The speed of light IS the speed of light. You cannot change it. c is universal. Your post is meaningless.
A "fast object" cannot travel at c. I assume that you have gone to the trouble of finding out the formulae.

A "bright line" doesn't apply here - any more than a temperature of Zero K. You can get as close as you like - depending on how much money and energy you are prepared to expend but you are still a massive object and you will follow the SR formulae,

 

[davidjoe]

I’m not suggesting that light be slowed. And I think that is clear in the posts. Light travels at C. But objects can be accelerated to just an iota under C.

If it is inconvenient that a striking difference exists in how two speeds are observed in all reference frames, when the difference between them could be the smallest possible, that doesn’t make the question or the post meaningless, does it?

 

[Motore]

Maybe take a step back, choose a simpler scenario, clearly define everything: which reference frame measures which thing, which objects have which speed RELATIVE to each other, ...
Do not forget, that each object can regard itself at rest and each object sees the light going at c.
For example you have the earth and you have a laser that has 0.999c velocity relative to the earth. You are standing on the earth and you "see" (not literally) that the light emitted from the laser is going at velocity c and the laser is slowly lagging just behind that light. Now you go sit a on the laser and you are at rest, stationary and you "see" that the earth is going by with 0.999c velocity, but the light from the laser is still going away from you at c and you (the laser) are not lagging slowly just behind the emitted light.