Down the relativistic rabbit-hole (Split from official news)

[Grench]

So, I started walking myself down this rabbit hole of how to make this work, then realized why it wouldn't. I'm leaving my path to get there intact for everyone's amusement.

Spoiler

Won't work, even if we ignore the relativity of light. Any change in time it takes to reach one end or the other from the center point will be mitigated do to the return trip.

Not if the center point is assumed to be moving.

oh is the giant space laser the thing you're trying to measure the speed of?

Yes.

in relativity, the laser apparatus is at rest with respect to itself, so light fired from the center will bounce off of the ends at exactly the same time and return to the center at exactly the same time. -- in the reference frame of the giant space laser.

Not if the central point of origin is in motion on the same axis it fires towards and away from.

in the reference frame of someone outside the laser, watching the laser go by, light fired from the center hits the back end of the laser first, then the front. on the return journey, it happens in reverse, so that the light meets in the middle again, at the same time.

Unless the entire system is in motion - which is what we're trying to measure here.

things that collide (at the same space-time location) always collide in every reference frame (light meeting back in the center, or being fired in the first place), but everything else is relative, even time.

Agreed.

You know, this sounds suspiciously similar to the Michelson-Morley experiment...

Very similar, but measuring two entirely different things. They were trying to detect the Aether. My idea is to detect 'absolute motion' by utilizing the peculiar nature of light's 'absolute velocity'.

LIGO utilizes a laser through a splitter down two tunnels on a L shaped system, bounces back and forth through the length of it multiple times from mirrors to augment the net effective length of the tunnel and examine the interference patterns of the beam when rejoined to determine if one tunnel got microscopically longer than the other due to fluctuations in space time from gravitational waves.

Using a similar principle, straighten out the track - and make it a real long one by re-bouncing the beams on their opposing ends.
Fire a laser through a splitter at the center down the paths in both directions.
Bounce them in their respective halves of the system a few thousand times.
Compare the interference pattern to see if one tunnel "got shorter" than the other -gradually-.

    |--------------------*+++++++++++++++++++|

If it is a momentary effect, that is a gravitational wave.
If it is a continuous effect over time that the beam fired down one tunnel had a shorter time to return than the corresponding beam fired down the other tunnel, then the measurement platform is moving in the direction of the shorter return time.

Each 'laser packet' is moving at the speed of light in opposite directions

    |--------------------*+++++++++++++++++++|
in motion ->
results in measurement
    |---------------------*++++++++++++++++++|

Why build it in space?
1. Calibration. Run it in one orientation, measure. Flip it over, run it again. Just like calibrating a bubble level.
2. Enables measurements with the test rig (huge as hell) at different velocities.

And why that won't work:

Spoiler

The beam fired in each direction must return to center for measurement of interference. Although the outbound paths may be of differential lengths (effectively shorter time to mirror in the direction of travel) - thus the impact of the light on either end may be different, the net time of arrival back at the center point would be the same - as the center point is also moving at the same rate as the ends.

So, what might work...
We know that everything in the universe is moving relative to everything else in the universe.
We know that light, regardless of origin or the velocity of the origin, travels at the same rate (with exotic exceptions).
Light does not inherit the added inertia of an origin in motion (this is key).

Make the 'racetrack' very long - not sure how long, but likely hundreds of miles, but of an exact known length. Place the detectors in the ends, not the center. Use insanely accurate, independent and synchronized clocks at the origin and detectors.

(Not real values.)
Light leaves the central point at T=0.0EXP-20.
Light arrives at the detector in the direction of travel at T=0.2EXP-20.
Light arrives at the detector in the reverse direction of travel at T=0.1EXP-20.

The light beam travels at the same absolute rate in both directions regardless of the motion of the point of origin.
The whole system is moving on the same path.
The light moving toward the 'rear' detector would have a shorter path to target than the light moving toward the 'front' detector.
The rear detector is moving toward the light.
The front detector is moving away from the light.
The difference in detection times can translate into the velocity of the system.

Can still flip it over to calibrate it.
The clocks and detectors would have to be insanely accurate.
Would need to be a very very long craft. The longer it is, the more accurately it could measure the difference in arrival times.

An analogy...
Jesse James is standing in the exact middle of a train car travelling at 50KPH. Jesse has two exact pistols with two exact bullets with two exact powder loads. The distance from him to the front and back walls is exactly the same. He fires in both directions at once, hitting two synchronized stopwatches causing them to stop. The bullets hit the front of the car and the rear of the car simultaneously - the bullets inherited his and the train's momentum. (ignoring lowered velocity gravitational drop blah blah)

Jenny James, Jessie's great-great-great-great-great-great granddaughter, stands in the center of a long compartment inside of a spaceship traveling 50000KPH. Jenny has two exact laser pistols that fire the same wavelength. The distance from her to the front (direction of travel) and rear ends of the compartment is exactly the same. She fires in both directions at once, hitting synchronized atomic clocks at either end causing them to register the hits. The light hits both clocks, but the rear (relative to direction of travel) clock shows that it stopped first by some tiny fractional amount - the light does not inherit Jenny's and the spaceship's momentum. Light traveling toward the rear of the craft travels at the same absolute velocity as light traveling toward the front of the craft. The rear wall of the craft, moving toward the light source shortens it's net path. The front wall of the craft, moving away from the light source lengthens it's net path.

So, I'm still convinced that we could hypothetically use the constant nature of the speed of light and the fact that it does not inherit momentum to create a detector to measure our absolute velocity through space. Velocity is a vector that requires no point of origin.

Just, remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour
That's orbiting at nineteen miles a second, so it's reckoned
A sun that is the source of all our power

The sun, and you and me, and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm at forty thousand miles an hour
Of the galaxy we call the Milky Way
...
The universe itself keeps on expanding and expanding
In all of the directions it can whiz
As fast as it can go, the speed of light you know
Twelve million miles a minute and that's the fastest speed there is
- Month Python et al.

But - those are all Newtonian/Galileo relative measures. Do we have anything currently that we can say truly has no kinetic energy? An experiment was recently launched to build a Bose-Einstein condensate in orbit so that it can be contained within a low gravity environment in hopes that it will last minutes instead of sub-seconds. It will still have inherent motion as sung above.

Would there be anything special to measure in a system of true 0 velocity?

Put on a set of long blinders and go for a ride in the passenger seat of a fast moving car while looking out the side window. A farmer's field appears to be just a blur of green (low signal to noise). But, if you stop, you can see that the field has furrow rows and a weed in the 40th row (high signal to noise).

What would we try to find, see, measure, test if we could truly, 'stop'? I have no idea really. Pure science at that point.
[doublepost=1527273645,1527272329][/doublepost]Addendum:
Good article on this concept of, "How fast are we going?"
https://www.scientificamerican.com/article/how-fast-is-the-earth-mov/
390K/s with reference to the CBR (Cosmic Background Radiation).

But - the CBR may be moving as well.

 

[ible]

@Grench you're still missing the point of relativity. if the clocks along the space-laser are synced and all travel the same speed, then there is no difference in time between when the light strikes the front-end of the ship versus the back-end, according to those clocks. in the reference frame of the space ship, everything is standing still, except the light which goes from the central source to the outer ends, and has the same distance to travel. the back/front-end of the ship aren't moving anywhere in that reference frame.

from an outside observer, watching the ship go by, she sees the light hit the ends at different times, according to her clock. (but if she looks at the clocks on the ship, she will see they agree on the time that the light hits them.)

the whole philosophical (and well-tested) foundation of relativity is that there is no way to tell how fast you are going, in an absolute sense, only how fast you are going relative to other things. as long as you (and your reference frame) are going a constant velocity, light behaves as if you were moving at no speed.

 

[Grench]

@ible I respectfully disagree.
For the light in this model to strike the fore and aft of a moving structure at the same moment would require the light to inherit the momentum of it's point of origin. The light cast forward literally must travel farther than the light cast back. Your statement assumes then that the forward cast light must move faster than the back cast light.

There is no difference in this model whether the light source is carried in the model object or a stationary point passed by it. A flash of light generated in a moving system or by a passing system will travel at a constant rate, regardless of the motion of the system.

Where you get into exotic properties and queasy theories is when the system approaches the speed of light - which this example does not.

Consider this: The light beam is being used to measure distance without reflecting back to source. There is a point of generation and a point of measurement. Using highly accurate and synchronized clocks, it is possible to measure that time traveled.

Move the target closer to the light source. The distance is shorter, the time traveled is less.

This time, move the light source very quickly toward or away from the target but flash it at the same distance. The light does not inherit this source momentum, the travel time is the same.

So, regardless of whether the light is in motion or static when it flashes, the light produced will travel at the same velocity in all/both directions. It does not inherit momentum from it's origin.

Two objects equidistant from a static light source are in motion with one moving toward the light source at 100Kph and one moving away from the light source at 100Kph. The light flashes. During the transition period of the light from source to the objects, each object will have moved (microscopically) either toward or away. Would you contend that the light will appear on both of them at the same instant?

My contention is that it is irrelevant whether the light source itself is static or in motion with the objects. The light it generates is relative to the point in space from which it was generated and the velocity at which the light source was moving at the point of generation is irrelevant. But - the motion of the detectors IS relevant to how far that light must travel prior to interacting with the detectors. If one is moving toward the light and the other away, there will be a difference, however slight, in travel time.

We may not have sensitive enough detectors or accurate enough clocks to register that difference over short distances. It may take a system as wide as a solar system to test it - I don't know.

But, what makes special relativity special is that light only moves at one velocity regardless of origin - or the velocity of that origin (no inherited momentum).

 

[Autian]

@Grench I didn't read the whole story about your topic, but for your measurement system you could use mirrors to avoid having the senders and receivers far away from each other.

 

[Grench]

@Grench I didn't read the whole story about your topic, but for your measurement system you could use mirrors to avoid having the senders and receivers far away from each other.

That is what I had originally considered, but that is a false path. We're not trying to determine the speed of light or the length of the travel - those are the known constants. The objective is to determine the velocity of the system.

Galileo decided that there is no velocity outside of reference. I.e. no true state of rest. Newton and Einstein liked it and moved on. The bokum theory of Aether was deemed false - rightly so. However, it was assumed that since there was no inherent stuff existing at a point state of rest, that there then could not be one. I find that to be an overstated conclusion.

The instant in space-time of the generation of light is effectively non-moving. I.e. the light generated will reach the same distances from origin in the same time period unless acted upon by another presence. The light generated will have the same momentum in all directions unless acted upon by another presence. Light, as it has no mass, does not inherit momentum from the motion of it's generating source. This does not preclude gravity from altering the momentum, direction, and net energy, of light (photons).

 

[PowerGod]

tl;dr

So, if you go at the speed of light, two months are almost endless ? Then the entire physics must be revised

 

[levi]

Indeed; we've long known the Pyra will take two months. We just never heard at what velocity.

 

[ible]

@Grench: you have to pick a reference frame. you've chosen the frame outside of the space craft (and your explanations of light hitting one side earlier than the other are just fine there). in that frame, you can measure the velocity of the space craft, because you are measuring it with respect to yourself (or the earth on which you live).

if you're inside the reference frame of the space craft, things are exactly as i said -- light hits both sides of the ship simultaneously. you can't measure the velocity of the ship using anything "inside" the space craft. the laws of physics are the same for someone who's standing still as for someone who's on a spacecraft traveling 0.9c.

the resolution of the paradox is that the two observers (in the two reference frames -- on the space craft and on planet earth) do not experience time the same.

this is exactly the problem we're considering, but with "trains" instead of a "space ship":
https://en.wikipedia.org/wiki/Relativity_of_simultaneity#The_train-and-platform

some other interesting paradoxes:
https://en.wikipedia.org/wiki/Ladder_paradox

@PowerGod -- a photon (traveling at the speed of light) would experience no time before seeing the Pyra in existence...

 

[Nintendo]

All this space-time, paradox, relativity, etc talk is all bullshit, because we all know that there are infinite multiverses/alternate universes out there and one where the Pyra is actually a handheld console made by Sony...or Microsoft (Windows) for that matter

 

[Djoga'Ro]

The light generated will have the same momentum in all directions unless acted upon by another presence. Light, as it has no mass, does not inherit momentum from the motion of it's generating source. This does not preclude gravity from altering the momentum, direction, and net energy, of light (photons).

The kind of momentum I know photons couldn't have. Otherwise they'd have mass and thus couldn't travel a the speed of light.

@PowerGod -- a photon (traveling at the speed of light) would experience no time before seeing the Pyra in existence...

So you're saying, we're too slow?

All this space-time, paradox, relativity, etc talk is all bullshit, because we all know that there are infinite multiverses/alternate universes out there and one where the Pyra is actually a handheld console made by Sony...or Microsoft (Windows) for that matter

Something is bullshit, because there may be something less relevant to us? Explain yourself!

 

[Mese96]

@Grench:
if you're inside the reference frame of the space craft, things are exactly as i said -- light hits both sides of the ship simultaneously. you can't measure the velocity of the ship using anything "inside" the space craft..

@ible As i have not much knowledge about all this (except from this thread) I hope you can explain it to me.

The train and platform paradox should be the same than @Grench s first try, (Mirrors in the spaceship vs. visual measurement of the lightflash), both times the light has to return to the observer.

If we measure the time the light takes at both ends of the spaceship, and consider this two measurement to be two observers, wouldn't they measure different times ?
If those observers remember their times and we would compare them afterwards, why would they show the same time ?

 

[levi]

Those two observers would (assuming the spaceship is reasonably rigid) be commoving with any other observer based on the spaceship, so should be in the same frame as any other.

But there is another experimental constraint that means we've only really been able to infer what happens in specific cases. Specifically, the usualy way of comparing photons is to combine two beams and observe the interference pattern, which means you need the two beams to arrive in the same place ; one observer. You can't really observe a single photon without consuming it. You could perhaps have two detectors which consume a photon then fire off a new one, and which have syncronised clocks which were synchronised at the center, and then moved very slowly to their ends, and I'm not sure exactly what you'd see then. It's a purely academic proposal though, since I don't think we can make those detectors yet, and we don't have clocks with the resolution of less than the frequency of light, unless maybe you could make radio photons of significantly less than 100kHz or so (long wave).

 

[ible]

But there is another experimental constraint that means we've only really been able to infer what happens in specific cases. Specifically, the usualy way of comparing photons is to combine two beams and observe the interference pattern, which means you need the two beams to arrive in the same place ; one observer. You can't really observe a single photon without consuming it. You could perhaps have two detectors which consume a photon then fire off a new one, and which have syncronised clocks which were synchronised at the center, and then moved very slowly to their ends, and I'm not sure exactly what you'd see then. It's a purely academic proposal though, since I don't think we can make those detectors yet, and we don't have clocks with the resolution of less than the frequency of light, unless maybe you could make radio photons of significantly less than 100kHz or so (long wave).

as long as we're not worried about quantum mechanics, we have things called beam splitters...
https://en.wikipedia.org/wiki/Beam_splitter

at any rate, we should remember the guiding principle behind relativity: that things happen relative to a given reference frame, and there's no absolute description of the world. but every one can agree on the laws of physics that govern their individual reference frames. and using those laws, they can understand how things happen in other people's reference frames. two things happening simultaneously is dependent on one's frame of reference, unless those things happen at the same place as well -- in which case those events are always happening at the same space-time point in every reference frame. (though perhaps translated in time or space.)

 

[Grench]

@Grench: you have to pick a reference frame. you've chosen the frame outside of the space craft (and your explanations of light hitting one side earlier than the other are just fine there). in that frame, you can measure the velocity of the space craft, because you are measuring it with respect to yourself (or the earth on which you live).

if you're inside the reference frame of the space craft, things are exactly as i said -- light hits both sides of the ship simultaneously. you can't measure the velocity of the ship using anything "inside" the space craft. the laws of physics are the same for someone who's standing still as for someone who's on a spacecraft traveling 0.9c.

the resolution of the paradox is that the two observers (in the two reference frames -- on the space craft and on planet earth) do not experience time the same.

this is exactly the problem we're considering, but with "trains" instead of a "space ship":
https://en.wikipedia.org/wiki/Relativity_of_simultaneity#The_train-and-platform

some other interesting paradoxes:
https://en.wikipedia.org/wiki/Ladder_paradox

@PowerGod -- a photon (traveling at the speed of light) would experience no time before seeing the Pyra in existence...

Please re-examine this:
https://en.m.wikipedia.org/wiki/Relativity_of_simultaneity#The_train-and-platform
I think you may be repeating this solution without fully understanding it.
You have the stationary observer reference correct. Perceives light striking the two ends at different times.
You have the center observer correct, but for the wrong reason. Break it down into momentary distances.
T0 light generated at observer in moving train car. A
T1 light encounters the back wall. B
T2 light encounters the front wall. C
T3 light from both walls returns to the moving observer. A
It happens in that order. With ideal detectors and clocks at both ends, that could be detected.

Light travel distances for moving observer:
AB = CA
BA = AC
AB < BA
AC > CA
AB+BA = AC+CA

So, the light in a moving object returns to center at the same time spans as a non moving reference. But, in the moving reference, the time to wall and wall to observer are different.

 

[ible]

your kung fu is only so so. take a relativity class. there are two reference frames (i.e. two different perspectives of what's happening). in the reference frame where you look at a moving train, everything is as you say. but in the reference frame of the train (i.e., you are on the moving train), things happen exactly as i say. light hits both sides of the train at the same time.

time is relative, which is why you're getting tripped up. events being simultaneous or not depends on what reference frame you're in. when events occur depends on your reference frame. you can imagine having a set of clocks everywhere in your reference frame, all traveling at the same velocity (which to you appears to be no motion), so you can record when and where things happen. for one observer (i.e. one reference frame), those clocks are on the moving train and record time and events as i say (light hits at the same time). for another observer, those clocks are on the planet, and record that light strikes the back and front of the train at different times.

if you take very simple principles (the laws of physics are the same in all reference frames), you come to this very conclusion, that light strikes the two sides of the train at different times in one reference frame, and at the same time in another. the laws aren't relative, the description of events is.

 

[Eight Bit]

What have I started....

 

[EricB]

What i think Grench is trying to explain is if you had 2 observers, one at each end of the train instead of one in the centre, they would both see the flash of light at different time.
The reason the central observer perceive both end to receive light at the same time is because it travels faster towards the back than the front and the return is faster from the front cancelling any delay that could be observed from either end.

 

[Kuro]

What i think Grench is trying to explain is if you had 2 observers, one at each end of the train instead of one in the centre, they would both see the flash of light at different time.

If these two observers are on the train (moving with it), they would see the light at diferent times as they are at difrent distances from the walls, but both would agree that the light beams hit both walls at the same time.

The reason the central observer perceive both end to receive light at the same time is because it travels faster towards the back than the front and the return is faster from the front cancelling any delay that could be observed from either end.

Light cannot move faster or slower, it always moves at c in relation to the observer, independently if the observer is moving at 0.9c, is at rest or is moving at 0.9 c in the other direction. Even if a different observer sees the same light and is moving in relation to the first, it would still see light moving at c in relation to himself. This is the reason why things like time dialation and space contraction occur.

 

[ible]

if the two observers are on train (and at the ends of the train) -- then the two at the ends agree that the light hits at the same time, and they will see it at the same time.

as Binky (IIRC) alluded to: the michelson-morley experiment tried to determine the absolute velocity of the earth with respect to an aether:
https://en.wikipedia.org/wiki/Michelson–Morley_experiment
they failed. but they used an apparatus that involved lights and mirrors and beam splitters and interference. (but no smoke.)

if in fact you could measure the absolute velocity of a space craft, what would it be with respect to? say we found out the earth is traveling 1000000 mph West. west with respect to what? the aether? (does not exist, see above.) this is a proof by contradiction. our initial hypothesis was wrong, we cannot measure absolute velocity, only velocity relative to other things. we measure velocity relative to our reference frame, which is to say, how fast things are moving with respect to us.

 

[Grench]

What i think Grench is trying to explain is if you had 2 observers, one at each end of the train instead of one in the centre, they would both see the flash of light at different time.
The reason the central observer perceive both end to receive light at the same time is because it travels faster towards the back than the front and the return is faster from the front cancelling any delay that could be observed from either end.

Close. Not faster, light is constant. Shorter distance to travel to the back of the moving train. but I think you were getting it.
[doublepost=1527571506,1527568830][/doublepost]

if the two observers are on train (and at the ends of the train) -- then the two at the ends agree that the light hits at the same time, and they will see it at the same time.

If the train is static, true.
If the train is moving, false.
The observer at the rear is moving toward the source and will encounter it ever so slightly before the observer at the front. Strictly due to the distance light traveled being different.

as Binky (IIRC) alluded to: the michelson-morley experiment tried to determine the absolute velocity of the earth with respect to an aether:
https://en.wikipedia.org/wiki/Michelson–Morley_experiment
they failed. but they used an apparatus that involved lights and mirrors and beam splitters and interference. (but no smoke.)

if in fact you could measure the absolute velocity of a space craft, what would it be with respect to? say we found out the earth is traveling 1000000 mph West. west with respect to what? the aether? (does not exist, see above.) this is a proof by contradiction. our initial hypothesis was wrong, we cannot measure absolute velocity, only velocity relative to other things. we measure velocity relative to our reference frame, which is to say, how fast things are moving with respect to us.

Your claims would require light to conditionally travel faster or slower. That is not special relativity.

Relativity: Gunshot inherits the momentum of the moving train. Both walls hit at once. Ricochet hits central observer at the same instance.

Special Relativity: Light does not inherit momentum of the moving train. Rear wall, moving toward light, gets hit first, front wall, moving away from light, gets hit second, though net time to central observer is equal. Differences cancel on return trip to the still moving central observer.

To a central observer they are the same. To an accurate enough pair of synchronized clocks on detectors at the ends? Different.
How accurate do they need to be? Insanely - likely more accurate than we have.
How synchronized? Quantum entanglement or close.
How long does the test chamber need to be? Longer the better.
Must be space based & maneuverable in place. Preferably at a Lagrange point oposite Neptune.

What is the point to "stopping"? No idea.
What could be the use in being able to measure? Pure science.[/quote]