linus tech tips gravity waves.. 6000

[GoldenLag]

3 minutes ago, tikker said:

Only minimally so though, the difference in index of refraction between vacuum and air is already just 0.03%, which is a large difference in pressure/density. So the speed of light shouldn't be that much different between LIGO and space, but it is taken into account.

Again. The speed of light is constant. What we persieve as a loss of speed is the detour of a photon from a straight path, or the absorbsion and re-emition of the photon.

 

They remove the particles tyst can interfiere as to remove any potentiaø interfirerence the photon might have. 

 

The path of the photon and speed is un-affected as long as it doesnt collide or interfierenwith any other particles.

 

Hence the desire to remove any particles from the laser tube. 

 

Just fyi, they dont technically need to use light to detects these gravity waves, it is just the simplest way of doing it. 

 

Im mostly nitpicking on this as the speed of light is constant. However the time it takes light to pass through a medium is slower, but the particle never stops moving at the speed light. 

[TechyBen]

48 minutes ago, KarathKasun said:

If you really want to make someone's head spin, we could go into the argument that the speed of light is not strictly constant.  Its a function of the curvature of space-time.  Gravity impacts it due to local time moving forward at a different rate near a gravity well.

 

A second is not the same here as it is in orbit for example.  And speed is measured in distance per unit of time.

AFAIK it's the opposite to how you mention it.

 

Speed of light is constant. Time is not. (Your post seems to say time is constant, speed of light is not)

That's the problem*. Speed of light is strictly constant (though speed through a medium is not! See Chekov Radiation).

 

 

*Well, not a "problem". Just a fact you must accept when seeing the data and information. Either GPS and satellites, orbits and space don't work and we are all dreaming, or relativity and the speed limit to light is true!

[tikker]

5 minutes ago, GoldenLag said:

Again. The speed of light is constant. What we persieve as a loss of speed is the detour of a photon from a straight path, or the absorbsion and re-emition of the photon.

Yes you are absolutely right. I should have said the effective speed of light in LIGO will be ever so slightly slower due to a slightly higher refractive index. The photons themselves will indeed always travel at c.

5 minutes ago, GoldenLag said:

The path of the photon and speed is un-affected as long as it doesnt collide or interfierenwith any other particles.

 

Hence the desire to remove any particles from the laser tube. 

Which is why they measure the residual refractive index and account for it  

 

50 minutes ago, KarathKasun said:

If you really want to make someone's head spin, we could go into the argument that the speed of light is not strictly constant.  Its a function of the curvature of space-time.  Gravity impacts it due to local time moving forward at a different rate near a gravity well.

 

A second is not the same here as it is in orbit for example.  And speed is measured in distance per unit of time.

Which is due to time dilation since in orbit you are less deep in the gravitational potential well and hence time runs faster compared to a clock on the Earth's surface; this is called gravitational time dilation.

 

The fact that the speed of light in a vacuum is constant is a key point of GR. So yes, it is strictly a constant and it is exactly defined as 299 792 458 m/s. See here as to how we came to the value it is: https://physics.stackexchange.com/questions/9314/why-is-the-speed-of-light-defined-as-299792458-m-s

[GoldenLag]

1 minute ago, TechyBen said:

AFAIK it's the opposite to how you mention it.

 

Speed of light is constant. Time is not. (Your post seems to say time is constant, speed of light is not)

That's the problem. Speed of light is strictly constant (though speed through a medium is not! See Chekov Radiation).

PBS Spacetime explains this better, but even with the difference in the length of a second, the speed of light is still preserved. 

 

Relativity is hard to wrap your head around, and i would be lying if i didnt say missunderstod a lot of it. 

[GoldenLag]

Just now, tikker said:

Yes you are absolutely right. I should have said the effective speed of light in LIGO will be ever so slightly slower due to a slightly higher refractive index. The photons themselves will indeed always travel at c.

Also, that would be the average speed of light through the tunnel through multiple passes. As long as the photon doesnt hit or interact with leftover particles it keeps moving at C. You will find that most of the time the particle will move the lenght of the tube at c (as in the time it takes to pass the lenght of the tube)

 

Any particle interactions will be accounted for using 2 detectors (which is what they have)

[GoldenLag]

Oh, BTW, these detections dont "prove" the excistance of gravitational waves. What they do is point to the fact that "something" causes these detections. And since this was predicted to occur using special relativity, this further provides evidence that special relativity is "correct" (nothing is proven in the scientific community as there are allways things that can change, like if supersymmetry is broken)

 

A theory predicted these detections and we have a phenomenom that can create them. Find tye object that created the phenomenom and you have effectivly shown that x caused y because z.

[Tarun10]

An intriguing video.

@GoldenLag Minutephysics is also a great channel for relativity.

[tikker]

13 minutes ago, TechyBen said:

*Well, not a "problem". Just a fact you must accept when seeing the data and information. Either GPS and satellites, orbits and space don't work and we are all dreaming, or relativity and the speed limit to light is true!

The only problem being we can never prove GR to be true, but we haven't been able to disprove it yet.

1 minute ago, GoldenLag said:

Oh, BTW, these detections dont "prove" the excistance of gravitational waves. What they do is point to the fact that "something" causes these detections. And since this was predicted to occur using special relativity, this further provides evidence that special relativity is "correct" (nothing is proven in the scientific community as there are allways things that can change, like if supersymmetry is broken)

 

A theory predicted these detections and we have a phenomenom that can create them. Find tye object that created the phenomenom and you have effectivly shown that x caused y because z.

Lol I was literally typing a similar response just now. Also gravitational waves come from general relativity, not special relativity.

[kilgore_T]

either way, how can such knowledge be utilized? 

[GoldenLag]

Just now, tikker said:

The only problem being we can never prove GR to be true, but we haven't been able to disprove it yet.

What we can say however is that this theory describes reality in a highly accurate manner to the point that we can consider it to be accurate untill it isnt. 

 

There is a reason why stringtheory and quantum machanics etc are a thing.

 

Afaik special relativity is perfect, but it is one of not, if not the best theory we gave at this moment. 

 

Which is why people call it "true". Which is a bad fallicy to fall into

[tikker]

5 minutes ago, kilgore_T said:

either way, how can such knowledge be utilized? 

Of gravitational waves? One major point this can help shed light on is the formation of intermediate mass black holes, for example. Typically black holes come in solar mass form or supermassive form (say ~10^6 solar masses). Both black hole mergers and intermediate mass black holes have been theorized to exist, but never observed. Then LIGO came online and the first thing it detected was the merger of two intermediate mass black holes. So we have confirmed both that intermediate black holes do exist and that black holes can in fact merge to form a new black hole.

[GoldenLag]

3 minutes ago, kilgore_T said:

either way, how can such knowledge be utilized? 

It allows us to construct accurate predictions of reality and then verify them using further experiments. 

 

That way we may abuse physics to the maximum in the future and we can create things without building them and know how they would behave. We also learn the limits of what can and shouldnt be able to be created.

[tikker]

6 minutes ago, GoldenLag said:

What we can say however is that this theory describes reality in a highly accurate manner to the point that we can consider it to be accurate untill it isnt. 

 

There is a reason why stringtheory and quantum machanics etc are a thing.

 

Afaik special relativity is perfect, but it is one of not, if not the best theory we gave at this moment. 

 

Which is why people call it "true". Which is a bad fallicy to fall into

This brings me back to my science philosophy course about being scientific and scientific paradigms haha. We must always work with falsifiable statements/theories, otherwise it's not a proper scientific theory. It's kind of scary to think about sometimes. No matter how often you confirm a theory, you only need one observation contradicting it and you've proven it false. Glad I'm an observationalist and not a theorist for now I guess  Though GR has stood up to its tests time and time again astonishingly well, so I'm with you on the statement that it seems to be a pretty damn (near) perfect theory so far.

[GoldenLag]

4 minutes ago, tikker said:

Though GR has stood up to its tests time and time again astonishingly well, so I'm with you on the statement that it seems to be a pretty damn (near) perfect theory so far.

It falls appart in extreme enviroments, which is why its not correct, but it keeps getting modified untill its wrong, or more correct.

 

I hope supersymmetry isnt broken. Even if all the induvidual symmetries are on their own

[tikker]

11 minutes ago, GoldenLag said:

It falls appart in extreme enviroments, which is why its not correct, but it keeps getting modified untill its wrong, or more correct.

Where does it fail? GR shines in extreme environments: precession of mercury, pulsar slowdown, black hole mergers were all predicted from GR and observations match the predictions so far.

[TechyBen]

35 minutes ago, GoldenLag said:

Oh, BTW, these detections dont "prove" the excistance of gravitational waves. What they do is point to the fact that "something" causes these detections. And since this was predicted to occur using special relativity, this further provides evidence that special relativity is "correct" (nothing is proven in the scientific community as there are allways things that can change, like if supersymmetry is broken)

 

A theory predicted these detections and we have a phenomenom that can create them. Find tye object that created the phenomenom and you have effectivly shown that x caused y because z.

Yep. Nothing to say it was not elves.

 

You know, this guy has it right:

 

PS, GR fails on the Quantum level. AFAIK it works in all other scales. "Extreme environments" is like only when you take one part of the equation/model to zero. IE, a Quantum/Singular measurement.

[GoldenLag]

4 minutes ago, tikker said:

Where does it fail? GR shines in extreme environments: precession of mercury, pulsar slowdown, gravitational lensing, black hole mergers were all predicted from GR and observations match the predictions so far.

Early universe its kinda iffy and at stupidly high temps its also kinda iffy.

 

Afaik at least. I am NOT by far any knowlegable person on GR . But i know some bits and bobs. 

 

Relativity will get better over time, but its not perfect. Which is why we build upon it

 

Edit: crucial word put in

Edited December 31, 2018 by GoldenLag

[TechyBen]

7 minutes ago, GoldenLag said:

Early universe its kinda iffy and at stupidly high temps its also kinda iffy.

 

Afaik at least. I am by far any knowlegable person on GR. But i know some bits and bobs. 

 

Relativity will get better over time, but its not perfect. Which is why we build upon it

Is it in high temps? (I'm interested in it, so am asking to find out more)

I've been playing in my head with how to allow for a QM special relativity style "matrix" of lorentz transformations... so knowing the current hard limits is good. I'd only known of the QM one so far, so have been working with moving from a single step wise/particle system up to a SR/GR system. Seeing how if fails with high density energy/heat would be great too.

 

Basically I'm livid at Steven Hawkins for giving up on the (AFAIK named) Boundary Condition of the black hole event Horizon/Big bang Time zero to Time +1 situation. If you can solve the gravity/GR for that, you solve QM gravity AFAIK, because you go from a singular (black hole, or start of the universe) to a multiple (space time fabric, macro sized objects etc). But sadly he both ran up to a brick wall on the math and observations, and decided to cop out and say "oh, the answer is we don't need an answer".

 

[Edit]

Ah, GoogleFu Knows all. Found it: https://en.wikipedia.org/wiki/Horizon_problem

I know of it, but by the other name "homogeneity problem". To some extent, I think it can be explained on a quantum level of the early universe, thus it's transitioning from those quantum interactions to the gravitational ones, and using such a model to see if it fits observed data.

 

[tikker]

10 minutes ago, GoldenLag said:

Early universe its kinda iffy and at stupidly high temps its also kinda iffy.

 

Afaik at least. I am by far any knowlegable person on GR. But i know some bits and bobs. 

 

Relativity will get better over time, but its not perfect. Which is why we build upon it

It works pretty far out; our current cosmological laws are derived from it (which admittedly have their flaws, but that depends on a boat load of other things besides GR). Once you get to the big bang, physics as we know it breaks down anyway. But even in the early universe we have not seen GR breaking observations yet, although constraints become more uncertain. We are justifying other assumptions with things like inflation, however.

[TechyBen]

3 minutes ago, tikker said:

It works pretty far out. Our current cosmological laws are derived from it. Once you get to the big bang, physics as we know it breaks down anyway. But even in the early universe we have not seen GR breaking observations yet. We are justifying other assumptions with things like inflation, however.

Yep. The early universe breakdown is on the distribution of matter, GR does not match predictions to the really early/small/dense/hot universe. Possibly because things were so "close" there were lots of QM interactions still going on. Or because our understanding of GR is wrong. Or we have got expansion/inflation wrong.

 

Though if we figure out Quantum Gravity, we can run a QM simulation from the "beginning", and GR from now back, and see where the models meet.

 

It's like Overclocking a GPU and a CPU. You know both are different, but they are plugged into the same universe PC. Under the hood both run on "logic gates", so currently we have GR (cpu) and QM (GPU) and are trying to find the underlying system/mechanics that both sit on top. XD

 

PS, GR also does not allow us to go from time zero to time + 1 though, AFAIK. QM does allow for such a "quanta" of change. Thus the black hole/big bang problem so far. GR does not explain it, and QM has a problem as we cannot scale it up to our current observations yet (without a way to go from QM -> GR in the models/simulations/calculations).

[GoldenLag]

7 minutes ago, TechyBen said:

Is it in high temps? (I'm interested in it, so am asking to find out more)

We are talking about temps higher than what we usually observe. Though its often related to early universe. 

 

7 minutes ago, tikker said:

But even in the early universe we have not seen GR breaking observations yet. We are justifying other assumptions with things like inflation, however.

We havent seen them, but we know it breaks down im circumstances that should have happened at some point. And physics as we know them breaking down in early universe is a sign that they arent 100% correct. If it was, then it would be able to explain it

[tikker]

2 minutes ago, TechyBen said:

Yep. The early universe breakdown is on the distribution of matter, GR does not match predictions to the really early/small/dense/hot universe. Possibly because things were so "close" there were lots of QM interactions still going on. Or because our understanding of GR is wrong. Or we have got expansion/inflation wrong.

 

Though if we figure out Quantum Gravity, we can run a QM simulation from the "beginning", and GR from now back, and see where the models meet.

 

It's like Overclocking a GPU and a CPU. You know both are different, but they are plugged into the same universe PC. Under the hood both run on "logic gates", so currently we have GR (cpu) and QM (GPU) and are trying to find the underlying system/mechanics that both sit on top. XD

Yeah unifying QM and GR/gravity is apparenlty very difficult  The homogeneity is a prime example of something that is a key assumption about our cosmology, and the arising problem we "solve" with inflation.

[WkdPaul]

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