cobaltoxide

> Based on conservation of energy

It turns out that energy is not conserved globally in General Relativity.

https://math.ucr.edu/home/baez/physics/Relativity/GR/energy_...

> If the wave imparts energy on an object and makes it move

The objects don't move. The space between them stretches and compresses.

Now, if the gravitational wave moves through a large massive object like a star or planet, the electromagnetic forces of the "stuff" in the object will cause it to resist this stretching or compressing. I think this does cause a very very very tiny "backreaction" to the gravitational wave, weakening it slightly.

> the wave and the force are the same thing?

Nope. This is a common misconception.

The difference between gravitational waves and gravity is a little bit like the difference between electromagnetic waves (emitted by an accelerating charge) and the electrostatic force (caused by a net charge at rest).

It's not possible to detect the effect of a charge far away, but easy to detect the propagating electromagnetic wave (light, ratio, etc).

Agree with jleahy.

I would add that considering counterfactual situations like "if the sun were to move instantly to the right" is of limited utility. That cannot happen (violates conservation of momentum). (Granted, other thought experiments have been quite influential in this field...)

"Gravity waves" are ordinary water waves, or other waves of a fluid, where gravity provides the restoring force:

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

They have absolutely nothing to do with gravitational waves.

Nonetheless, in the gravitational wave community (i.e. LIGO) we don't usually ever talk about true "gravity waves" so we use the terms interchangably.

The exception is that "gravity waves" in the Earth and the atmosphere can couple to LIGO through ordinary Newtonian gravity, which is something we have to think about and exclude.

Gravitational waves do not behave in the way you have described.

> I understand that to mean that on Earth we've managed to detect that increase from 2e20N to 3e20N.

This not what how gravitational waves behave. This assumption is not correct and will confuse you.

I believe this answer is nonsense.

> Is it possible to compress space?

The geodesic distance between inertial test masses increases and decreases.

Colloquially we say that space has stretched and compressed.

Geodesic distance can be measured by the time it takes light to travel between the points.

Inertial test masses can be simulated by hanging them from fine wires (LIGO) or by setting them up in an orbital constellation (LISA).

Here is an introductory paper on that exact topic:

"If light waves are stretched by gravitational waves, how can we use light as a ruler to detect gravitational waves?" https://universe.sonoma.edu/moodle/pluginfile.php/89/mod_res...

The way I explain it: The light already inside the arm cavity is stretched. But newly entering light is not. We are basically using the light as clock to measure the length of the arm. When the arm is in the "stretched" state, light will take longer to make a roundtrip in the arm. It will accumulate slightly more phase, which is measured interferometrically.

It is important that the storage time of the light in the arm is short compared to the period of the gravitational wave.

Gravitational wave detectors can only detect oscillatory signals, not static ones.

Gravitational waves are waves of the metric tensor. Einstein's field equations provide the "restoring force."

Importantly, gravitational waves are not waves of Newtonian gravity. Gravitational waves do not "push and pull" along the direction of propagation. They stretch and compress space along axes perpendicular to the direction of propagation.

> E.g., if the moon suddenly lurched towards the Earth, we'd perceive an increase in gravity between the two. But that would be a semi-permanent change in the strength of that attraction between the two objects; not what I'd think of as a wave-like fluctuation.

Indeed, gravitational waves do not work this way.

Unfortunately it is hard to explain gravitational waves without significant math.

In fairness, even Einstein himself waffled over whether gravitational waves would be a real effect predicted by the theory. Then it took nearly a century to detect them experimentally, and there were plenty of doubters along the way.

The results one gets from intuition are generally incorrect in important ways. Here's a derivation of a wave equation from Einstein's field equations:

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

A more helpful introduction for a layperson might be the paper titled "Gravitational Waves on the back of an envelope":

https://aapt.scitation.org/doi/10.1119/1.13627

But, infuriatingly, that paper does not seem to be open-access. Here's someone's scanned copy:

https://www.ru.ac.za/media/rhodesuniversity/content/mathemat...

Agreed, the MW definition does not seem to be correct.

Shouldn't it be called Rustbang?

Came here because I thought maybe AS8003 was another disappearing aircraft like MAS370.

https://www.fun-mooc.fr/en/courses/live-object-programming-p... ?

> There was never a reason for high status individuals to be on clubhouse

Sounds like early-stage Quora.

Not enough volume.

And you have to maintain water in the tower in order to keep the water distribution system pressurized.

Reminds me of the article "Were Early Modern People Perpetually Drunk? (2016)"

https://news.ycombinator.com/item?id=13535868

Are you referring to Uber as "highest regarded engineering org"? :grimmace:

I had totally forgotten about Opera.

If they are "independent contractors" then who exactly is paying for this time off, etc?

Shout-out to UC Berkeley's Open Computing Facility (OCF) which has managed to host this content for decades.

In what way would government investment help here? The main players already have tons of funding.

Also, why should self-driving be a government priority?

Do corporations experience emotions?

That may be true, but I've had good luck asking recruiters for feedback after getting bad news. They usually give some good advice or feedback - over the phone, of course, never in writing. Typically they say something like "You were really strong in X but the hiring manager is looking for someone with more Y." One recruiter told me that the HM had given me the thumbs down saying I was "insufficiently succinct" in my answers! But even there, I had good rapport with the recruiter and he was able to suggest other roles within the company.

> But the result is beautiful.

Uhhhh, gonna have to disagree there.

How many lines of code is it?

I suspect that, typically, when people mention ISO-8601, they really mean simply "YYYY-MM-DD" and are not seeking to incorporate all the other complications and details of the standard.

Can I use this now? Is there a getting-started guide or gallery of examples?

Another physics PhD chiming in here. I have never before noted the difference between "multiplier" and "multiplicand". The whole article has me rolling my eyes.

In fact, I would argue that multiplication being associative shows that this distinction is meaningless.