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"frequency-dependent quantum squeezing"

Very exciting!

I mistakenly read that as “frequency-dependent quantum sneezing.” I should go to sleep…
Squeezing has been around for a while, in that I remember studying it in 1989. Squeezing means you can go below the limits imposed by the Heisenberg uncertainty principle for a short period of time, provided the average uncertainty is above the limit. It seems that LIGO is using squeezed light in their interferometer.

[1] https://en.wikipedia.org/wiki/Squeezed_states_of_light

More specifically it looks like they can do squeezing dynamically around a target frequency whereas before they had to pick a fixed frequency a priori.
> Squeezing means you can go below the limits imposed by the Heisenberg uncertainty principle for a short period of time

This is not entirely accurate. The Heisenberg uncertainty (or Schrödinger/Robertson) uncertainty limits still work. If you somehow break those limits you disprove quantum mechanics.

Squeezing just reduces the uncertainty in one observable by increasing the uncertainty in the other observable.

> provided the average uncertainty is above the limit

> reduces the uncertainty in one observable by increasing the uncertainty in the other observable

Seems like you’re both saying the same thing with different wording

I somewhat disagree. You can check out the Heisenberg uncertainty principle here

https://en.wikipedia.org/wiki/Uncertainty_principle

As you can see there is no mention of time in any of the standard inequalities (excluding the energy/time "uncertainty principle" which is not relevant here). You can not go below the limit imposed by the Heisenberg uncertainty principle for any duration of time without disproving quantum mechanics.

What LIGO does is break some metrological "limit" which is derived by combining the uncertainty principle with some assumptions about what your measurement procedure looks like and what your states are.

Unsurprisingly if you use different states you can break this "limit".

It's not an average. The limit is σ_x * σ_p >= hbar/2, where x and p are any two conjugate variables.
This is a better interpretation and also conforms to experimental / theoretical backing that tries to deemphasize “time” as a measurable.

Refining the time metric in the Heisenberg limit to be couched in entropy is also common. Time is not really trusted as a fundamental quantity due to lack of observerless descriptions, and entropy and time have ultra similar properties, and indeed may be fundamentally linked. They both seem to flow in one direction and are impossible to reverse in the absolute sense.

The point of “squeezing” is to push a lot of uncertainty in one variable so that one could measure much lower variance in the other variable post-squeeze… both pre and post squeeze are Heisenberg bound, but post-squeeze uncertainty is lower than pre-squeeze and therefore “under the limit” pre-squeeze.

When I spoke to ligo for a position they were talking about amplitude / phase uncertainty trade offs.

The articles says it originated theoretically in the late '70s, and was first demonstrated experimentally in 1986.
So the "Heisenberg Compensators" in Ster Trek's transporters now have a basis in reality. Denise and Mike Okuda should be proud.
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Seems like 'limit' is a misnomer here.
It's a limit similar to how the resolution of a N-bit analog to digital converter (ADC) is limited to 1/2^N. You can break that limit by adding noise, known as dithering[1], to get even better resolution.

Like with the squeezed light in LIGO there is no free lunch, but the idea in both cases is to pay for the lunch with something you have plenty of or otherwise don't care that much about, rather than your limited amount of money.

With dithering you have to filter out the noise, but if your ADC can sample faster than you require then you just oversample and average.

For LIGO they care very much about the phase accuracy but not so much the amplitude, so they pay by having worse amplitude certainty[2].

[1]: https://www.allaboutcircuits.com/technical-articles/what-is-...

[2]: https://www.ligo.caltech.edu/video/ligo20231023v2

I would argue that dithering is fake resolution, so you're not exceeding the limit in the information theoretic sense. Perhaps a better analogy would be compressed sensing on a sparse, structured signal where you can seemingly violate Nyquist but only because you have additional information about the sampled signal.
I wonder if there was a collision of super heavy black holes, would we feel the gravitational waves by ourselves
If you're close enough to feel gravitational waves, it's unlikely for humans (or even planets) to survive intact.
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I don't think so, or as someone else pointed out, it would rip the earth apart before we felt it.

I'm no physicist, but, the earth is massive so is influenced a lot more by external gravity than the specs on its surface that are people. Take the moon, it's a huge object hovering over the planet (effectively, it's slow moving, the earth rotates underneath it), its gravity pulling on seawater and causing ebb and flow. But we cannot feel its gravitational effects ourselves.

Colliding super heavy black holes wouldn't do it. For us to feel a gravitational wave, it's wavelength would have to be small compared to a human body, which in turn means the pair of bodies emmitting those gravitational waves would have to be separated by at most a few meters, but supermassive black holes would merge long before they got to that point. Indeed a pair of bodies capable of producing gravitational waves with both the frequency and the amplitude probably can't physically exist.

One could imagine though some configuration of many pairs of black holes, orbiting at different frequencies to interfere with one another and produce a sharp beat, perhaps with other mass configured to act as focusing lenses. Still almost certainly wouldn't exist in nature but a cool potential scifi concept.

I think it's better to write 10 quadrillions rather than 10 thousand trillions. Also I think frequency and power measurement precision are not mutually limited by the Heisenberg principle, as E = ħω .
As awkward as "thousand trillion" is, trillion has the advantage that it shows up in the news on a regular basis. I can much better be impressed by cutting a hair by a nation's debt than I can by cutting the same hair into a quadrillion pieces.
I'd say that people who read about LIGO and quantum limit, also understand quadrillion.
Some countries have national debt in the quadrillions, e.g. Japan and Indonesia.
Nope, use scientific notation if numbers become so unwieldy.
Depends on the audience. Laypeople generally know numbers up to a trillion, hence the choice of language. I only happen to know what a quadrillion is because I've played Cookie Clicker. I have trouble with scientific notation, because I'm not a scientist or mathematician and have no interest in it.

TL;DR, know your audience and cater to them if you want people to be interested.

I hate LIGO because it shouldn't work on paper, and few seem to actually understand it.

1. If you have a light wave in the universe, and you "hang" a mass by each valley and trough of the light wave, and then you squash and stretch the universe, the masses stay connected to the valleys and troughs of the light wave. Said another way, when you squash and stretch space, lightwaves within that spacetime are also squashed and stretched.

2. LIGO claims to work by measuring the squashing and stretching space with light. However, as we just learned, squashing space also squashes light waves. So the LIGO arms and light waves in the arms are all compressed together.

Said another way, LIGO can't work because the ruler itself is squashing as space squashes, so you can't measure if space is compressing.

LIGO does work, but if you can't explain how it works despite this description, then you don't understand LIGO.

> LIGO does work, but if you can't explain how it works despite this description, then you don't understand LIGO.

So uhh... how does it work in spite of that description?

It has two arms at right angles to each other, and measures the difference between the two length changes via laser interferometry. This gets you the component of the wave polarized along the corresponding axes.

No clue why GP thinks it "shouldn't work": it's an extremely difficult engineering problem, but the physics of it is relatively straightforward.

Yeah, the physics is straightforward. Even "laser interferometry" is super simple to explain. It is getting enough resolution and noise immunity from laser interferometry where all the interesting stuff is.
I think GP's point is that you can't measure changes in the length of an arm if the ruler you're using is changing in the same way.

I think this misrepresents the situation, but I can't say how, so I can't dismiss it quite so quickly.

The "ruler" you're using is the other arm, which doesn't change in the same way: one axis stretches while the other compresses.
True, but with only two arms, I think LIGO is somewhat directional, is it not?

Stronger signals from some black holes depending on which way they're oriented relative to the arms. And if there were many different simultaneous signals, some could mask the others.

Clearly, we need a 3-armed, space-based LIGO. Or better, a dozen of them.

There are two LIGO interferometers in the US [0], Virgo in Italy [1], GEO600 in Germany [2], something in Japan [3] and something being planned out being built in India. There is LISA as space-based project in the works too [4].

[0] https://en.m.wikipedia.org/wiki/LIGO

[1] https://en.m.wikipedia.org/wiki/Virgo_interferometer

[2] https://en.m.wikipedia.org/wiki/GEO600

[3] https://en.m.wikipedia.org/wiki/KAGRA

[4] https://en.m.wikipedia.org/wiki/Laser_Interferometer_Space_A...

"but the physics of it is relatively straightforward."

Amusingly Einstein both identified gravitational waves in his then new general relativity and then changed his mind about whether they existed. Indeed he had found three different types of these waves, and two of them were simply coordinate artifacts (they could be made to travel at any speed, Eddington famously quiped that they could be made to move at the "speed of thought"). The third type however didn't have this problem (though again here Einstein would write a paper where he claimed these gravitation waves required singularities, but these turned out these were all coordinates singularities .... sort of like how late and long coordinates misbehave at the poles)

In some ways the physics of it is straightforward, in other ways....not so much.

I think you have an intuitive mental model of how it works, but don't actually understand it, or aren't able to explain it well.

This question is important enough that there have been papers written on it. I suggest you read https://pubs.aip.org/aapt/ajp/article-abstract/65/6/501/5300... which may strengthen your understanding.

> This question is important enough that there have been papers written on it. I suggest you read https://pubs.aip.org/aapt/ajp/article-abstract/65/6/501/5300...

This is a physics education journal: its papers are supposed to be interesting and accessible to undergrads, not on the frontier of the field.

What the linked paper amounts to is noticing that the sensitivity of a detector depends on the relative length scales of the arms and the waves you're trying to detect. This is true, and also one of the first things you would consider when figuring out what size your detector should be. It's a good homework problem, but not news to anyone actually working on LIGO.

I legitimately find your cognitive dissonance interesting. I think you're on the other end - you may understand the fundamentals so well that your brain isn't processing the question / conundrum in the way that others see it. Honing in on the the scales of the arms as your reaction the paper is why I think this, as that's not related to the problem. And, well, you said it yourself, you don't understand the question:

> No clue why GP thinks it "shouldn't work"

It's also possible you think that this is all about laser interferometry, and aren't properly considering how it could work in the context of compressing space, since a laser interferometry system in compressed space wouldn't produce interference.

What you really mean is that you don't understand how LIGO works and neither do any of the reporters who try to explain it. And so the explanations that are available in public do not really give an insight into what is happening.

That's unfortunately true for a lot of physics. For example, there are very few good explanations available for what is electric current and it is pretty funny observing even people with lots of experience offer the same lame, false explanation.

> Said another way, LIGO can't work because the ruler itself is squashing as space squashes, so you can't measure if space is compressing.

I think the chief confusion here is that you may be thinking the light arrives at the detector in the same amount of time regardless of spacetime curvature. That is, the the ruler is itself squishing.

But what needs to be considered is the constant speed of light.

This implies that what happens is, in the presence of additional curvature, and constant speed of light, the additional distance traveled will have appeared to slow the light.

In the laser interferometer this registers as interference.

https://m.youtube.com/watch?v=ajZojAwfEbs

It is also worth noting that any claims of detection are thoroughly investigated and confirmed with other detectors.

> It is difficult for a single LIGO detector to confirm a gravitational wave signal on its own. The initial discovery of gravitational waves required that the signal be seen in both detectors (Hanford and Livingston).

https://www.ligo.caltech.edu/page/what-is-ligo

> the additional distance traveled will have appeared to slow the light.

I thought it made the light reduce in frequency. Or did I misunderstand?

You didn't misunderstand. A sudden stretching of space cannot change the number of peaks and troughs as they go past, but since those peaks and troughs are now slightly further apart, the frequency of the light is slightly lower, and the light takes slightly longer to travel. This applies to light that is already in transit. Of course, as the gravitational wave passes by, the length/frequency returns to normal again.

New light that is emitted at one end of the journey while there is a stretching status will have the same frequency as normal, and just see the longer journey. In fact, the gravitational waves that LIGO is able to detect are slower than the time it takes for light to make the journey, so the stretching is effectively gradual, and the detector is basically an extremely accurate length measurement. The gravity waves aren't fast enough to make the light changing frequency a thing that needs to be worried about.

> It is also worth noting that any claims of detection are thoroughly investigated and confirmed with other detectors.

This is the thing I (as a layperson) can't really wrap my head around yet; there's gotta be so much interference from so many different sources, there's gotta be some impressive data processing going on to filter out anything not relevant to their core measurements, and then THAT data will have to be compared to that of other detectors.

This device, the LHC, space telescopes, really cool and all if you look at the published pop-sci results, but the actual data is like... individual photons captured by a worldwide network of detectors and processed / data analyzed into the first "photo" of a black hole.

I believe there’s three LIGO detectors stationed in different parts of the world which greatly helps with the noise reduction.
LIGO has three rulers. The difference among the rulers results in measurement. (Two rulers are on site, the "third" is the other locations.)
People have down voted the parent comment but I'm not sure why. Perhaps it was the tone, but it caused a series of informative explanations that may not have arisen without this post.
What is the purpose of this? How does this benefit the inhabitants of Earth? I don't have a PhD, so I can't come up with a reason for it.
What's the purpose of a baby? Is it just a future worker, or does the baby have intrinsic value?
I'm asking an honest question, not slandering the scientific endeavor.
What purpose did the moon landing have? It didn't benefit anyone!

But the surrounding research and advancements in all scientific fields did!

The point of science is to learn. Maybe there's nothing practical to LIGO, maybe in 200 years we have artificial gravity. There's no way to know.
Thanks. It just seems so far out to me that I have a hard time envisioning why spend time and energy in this.
A reasonable mental model is to view LIGO as a (weird) telescope. Most telescopes work by detecting some form of electromagnetic waves while LIGO works by detecting gravitational waves, but its purpose is pretty much the same as any telescope. To tell us stuff about what is happening out in the universe.
What possible purpose could learning more about a hunk of random crystal and some electrodes have? Oh, that seems to have some interesting properties after all.

Some crazy dudes want to build a flying machine. Totally impossible, it will never happen. Just stick to horse-drawn carriages, also let’s try to squeeze a bit more efficiency from that coal-powered steam boiler over there...

And on and on and so forth. Breakthroughs and just general advances in science look like crackpot ideas or wastes of time until they aren’t. Fundamental research is almost always a good thing, no matter how out there or wildly impractical it may seem.

You can think of LIGO as being the first new way to directly see the universe since the invention of radar telescopes. Our ability to measure the otherwise unmeasurable, such as black hole and neutron star collisions, could lead to a better understanding of dark matter/dark energy, astronomy, and both physics and astrophysics.

This expands the reach of knowledge of humanity; once made available, who knows how future humans will use these new discoveries to benefit mankind. Claude Shannon developed information theory well before networked computers were invented, but it's now critical to many disciplines and products you use every day.

Meanwhile, the actual engineering challenges overcome in the building (and refinement) of LIGO are directly applicable to development of more accurate sensors, quantum computing, and precision engineering - all of which will touch the lives of Earth's inhabitants without most of them even being aware of it.

Like a number of other large scale scientific instruments like the LHC, it's provided proof of theories held for a long time - in this case, that gravity can propagate in waves, and that merging black holes cause these waves, and in turn that black holes do in fact merge or rotate around each other causing huge waves in spacetime.

Is it conclusive evidence? No, ultimately it's just a data point. But it's evidence.

Take another one; Einstein hypothesized that light is influenced by gravity, and came up with an experiment that didn't need super high tech instruments; observe the stars next to a solar eclipse and see if their position is different from normal. A few years later there was an eclipse, multiple people made the observations, and his hypothesis was proven correct.

Thanks to that experiment, we now have telescopes that can use gravitational lensing from galaxies to look at the farthest reaches of space.

LIGO by itself serves "very little" purpose, just watching for gravitational events that are theoretically possible and checking if they happen for real. It actually confirmed that these events exist a while ago[1], and now it's "just" looking for more things we already know exist.

in my opinion, the point of LIGO is no longer in detecting these gravitational events anymore tbh. Doing that is cool, and will bring us more data points about the events, but it's unlikely to ever yield "new science" like that.

Instead, LIGO (and Virgo) excel in exactly the kind of thing that we see in this article: to push the barrier of what we can do in this hyperspecific use-case, finding ways to do "new" engineering that would not make sense for other commercial projects yet and finding out how to implement cool solutions. The fairly consequent amount of funding and the extra focused goal it is aiming for will lead to new techniques and technologies that might have an impact.

Now, is there a guarantee that this new technology will have a larger impact than "better detectors"? No. Actually, there's no guarantee about anything coming out of LIGO ever, no more than out of the LHC[2] or ITER[3] or the ELT[4] will give us new science. But putting all of your eggs in the same basket is a bad solution for making more science, and there's enough room in science budgets to try a few dozen monumental projects and see what sticks.

[1] https://en.wikipedia.org/wiki/First_observation_of_gravitati...

[2] https://en.wikipedia.org/wiki/Large_Hadron_Collider

[3] https://en.wikipedia.org/wiki/ITER

[4] https://en.wikipedia.org/wiki/Extremely_Large_Telescope

There is a chance that LIGO will detect something we don't expect. I believe that has happened quite a bit with optical microscopes and telescopes.

Edit: Actually you said that but consider it unlikely which I absolutely can't argue with.

>"Now, writing in the journal Physical Review X, LIGO researchers report a significant advance in a quantum technology called "squeezing" that allows them to skirt around this limit and measure undulations in spacetime across the entire range of

gravitational frequencies

detected by LIGO."

Gravitational frequencies -- now that term is going into my 2023 lexicon...

(Note that I don't know what it means, just yet -- but it sounds like it could be useful in the future; it sounds like there is an interesting idea (or a series of interesting ideas) there...)

It's just the frequency of a gravitational wave, it's not very impressive.
I don't believe that I stated an opinion relating to the impressiveness or non-impressiveness of the phenomena (or the purported phenomena) as the case may be...

"Interesting" != "Impressive".

What would impress me however (greatly I may add!) -- is if you knew how an average experimenter with, say, $100 or less of lab equipment -- could create and test (and therefore know to be real) gravitational waves -- without relying on, or repeating any news articles or other secondhand information source...

In other words, with respect to gravitational waves, "I want to see them with my own eyes" -- to believe them...

The problem with the media today is that everybody parrots what everyone else is saying (https://en.wikipedia.org/wiki/Echo_chamber_(media) ), nobody seems to think for themselves, and it seems that very few people do actual firsthand experiments to verify media claims...

I'm not saying that gravitational waves don't exist -- far from -- but the standard of proof I require is via firsthand experiment -- rather than secondhand hearsay about someone else's experiment...

Firsthand experiments usually lead to greater understanding -- whereas secondhand hearsay usually leads to greater confusion...

So, show me a guaranteed experimental way that someone with $100 or less of lab equipment could create their own gravitational waves with (and subsequently know them to be real via their own firsthand witnessing of one)... and I'll be impressed!

Very impressed, in fact!

Oh, sorry for taking so long to respond. You need very expensive equipment to detect gravitational waves at all, and it's not off the shelf either. They might be able to get the cost for a leading edge facility under 1 billion dollars and 5 years build time depending on how well you manage it. I'm saying the frequency itself is not profound, it won't give you psi powers or expand your mind any more than the frequency of ocean waves will.
I'm guessing that Aquaman -- would respectfully disagree with that assessment! :-) <g> :-)

But humor aside, an interesting question might be:

Why is frequency -- such a fundamental component of Physics?

What is the first principle or first principles -- that gives rise to frequency?

We might step back a step, and say (and or observe) that waves and wave-like phenomena are present in many aspects of this Universe -- both seen and unseen.

So do waves give rise to frequency -- or is it the other way around, does frequency give rise to waves?

We see both phenomena present in the concept of energy -- energy of all sorts.

We also see the concept of imbalance -- over half a wave cycle, and balance (or rebalance, if you will) over a full one...

Which is in turn connected to the concept of vibration, oscillation, repetition and reversal (over a period of time, aka periodicity)...

So, frequency is not profound?

It seems to be intricately, intricately connected to a whole bunch of physical phenomena -- that are indeed profound!

But that being said (and to agree with you!) -- no it probably won't give you psi powers or expand your mind any more than the frequency of ocean waves will.

(Unless of course you somehow happen to be Aquaman! <g> :-) <g>)