kloch

We can't even measure the gravitational constant to more than about 4.5 significant digits. Most other natural constants are in the 7-12 digit range and improving along with our technology. Measurement of big G hasn't convincingly progressed since the vacuum tube era.

We have a lot more to learn about gravity, especially at laboratory scale and smaller.

They collected data on both back in 2017. It took until now to develop the image processing techniques to account for the rapid changes in the accretion disk around Sag.A*.

For Interferometry to work the data from different baselines has to be collected at the same time so waiting 6 months does not help. Spacecraft could theoretically be used to extend the baselines but the volume of data to be transferred is prohibitive with current spacecraft comm tech.

Even on Earth they resort to shipping cases of hard drives instead of transferring over the Internet.

One technique where simply waiting 6 months works very well is in measuring parallax. The Gaia spacecraft takes advantage of this.

It's actually one of the sharpest images ever made - in terms of angular resolution. The Sag.A* ring is about 51 microarcseconds in diameter. The EHT has a theoretical resolution of ~25 micro arcseconds. For comparison NirCam on Webb has a pixel resolution of 70 miliarcseconds (about 2800 times worse resolution than EHT).

The reason it looks blurry is that the black hole features are close to the resolution of EHT so it's only a dozen or so pixels worth of information enlarged to typical image size.

EHT is essentially a radio telescope with a dish the size of the Earth. The only way to get higher angular resolution is to use higher frequencies (which they are working on) or use radio telescopes in space to get longer baselines than the diameter of the Earth.

One of the findings they announced at the press conference is that the spin of the black hole is not aligned with the galactic plane but is tilted "towards us" so that it is viewed face on.

How unexpected is that?

Additional dimensions also give you new ways to define angles.

  2D: axis-axis (a-a)
  3D: a-a, plane-axis (p-a)
  4D: a-a, p-a, plane-plane (p-p), volume-axis (v-a)

etc.

Here is the construction of the n-ball volume and n-sphere surface area constants up to n=26. Those denominators get crazy.

  double nbv[27];
  double nss[27];

  // n-ball volume constants (index is exponent and n-ball dimension)
  // nbv[n] = nss[n-1]/n (n > 0)
  // nbv[n] = 2pi * nbv[n-2]/n (n > 1)
  nbv[0]=    1.0;
  nbv[1]=    2.0;
  nbv[2]=              M_PI;
  nbv[3]=    4.0 *     M_PI        / 3.0;
  nbv[4]=          pow(M_PI,  2.0) / 2.0;
  nbv[5]=    8.0 * pow(M_PI,  2.0) / 15.0;
  nbv[6]=          pow(M_PI,  3.0) / 6.0;
  nbv[7]=   16.0 * pow(M_PI,  3.0) / 105.0;
  nbv[8]=          pow(M_PI,  4.0) / 24.0;
  nbv[9]=   32.0 * pow(M_PI,  4.0) / 945.0;
  nbv[10]=         pow(M_PI,  5.0) / 120.0;
  nbv[11]=  64.0 * pow(M_PI,  5.0) / 10395.0;
  nbv[12]=         pow(M_PI,  6.0) / 720.0;
  nbv[13]= 128.0 * pow(M_PI,  6.0) / 135135.0;
  nbv[14]=         pow(M_PI,  7.0) / 5040.0;
  nbv[15]= 256.0 * pow(M_PI,  7.0) / 2027025.0;
  nbv[16]=         pow(M_PI,  8.0) / 40320.0;
  nbv[17]= 512.0 * pow(M_PI,  8.0) / 34459425.0;
  nbv[18]=         pow(M_PI,  9.0) / 362880.0;
  nbv[19]=1024.0 * pow(M_PI,  9.0) / 654729075.0;
  nbv[20]=         pow(M_PI, 10.0) / 3628800.0;
  nbv[21]=2048.0 * pow(M_PI, 10.0) / 13749310575.0;
  nbv[22]=         pow(M_PI, 11.0) / 39916800.0;
  nbv[23]=4096.0 * pow(M_PI, 11.0) / 316234143225.0;
  nbv[24]=         pow(M_PI, 12.0) / 479001600.0;
  nbv[25]=8192.0 * pow(M_PI, 12.0) / 7905853580625.0;
  nbv[26]=         pow(M_PI, 13.0) / 6227020800.0;

  // n-sphere surface area constants (index is exponent and n-sphere dimension and n-ball dimension - 1)
  // nss[n] = 2pi * nbv[n-1] (n > 0)
  nss[0]=     2.0;
  nss[1]=     2.0 *     M_PI;
  nss[2]=     4.0 *     M_PI;
  nss[3]=     2.0 * pow(M_PI,  2.0);
  nss[4]=     8.0 * pow(M_PI,  2.0) / 3.0;
  nss[5]=           pow(M_PI,  3.0);
  nss[6]=    16.0 * pow(M_PI,  3.0) / 15.0;
  nss[7]=           pow(M_PI,  4.0) / 3.0;
  nss[8]=    32.0 * pow(M_PI,  4.0) / 105.0;
  nss[9]=           pow(M_PI,  5.0) / 12.0;
  nss[10]=   64.0 * pow(M_PI,  5.0) / 945.0;
  nss[11]=          pow(M_PI,  6.0) / 60.0;
  nss[12]=  128.0 * pow(M_PI,  6.0) / 10395.0;
  nss[13]=          pow(M_PI,  7.0) / 360.0;
  nss[14]=  256.0 * pow(M_PI,  7.0) / 135135.0;
  nss[15]=          pow(M_PI,  8.0) / 2520.0;
  nss[16]=  512.0 * pow(M_PI,  8.0) / 2027025.0;
  nss[17]=          pow(M_PI,  9.0) / 20160.0;
  nss[18]= 1024.0 * pow(M_PI,  9.0) / 34459425.0;
  nss[19]=          pow(M_PI, 10.0) / 181440.0;
  nss[20]= 2048.0 * pow(M_PI, 10.0) / 654729075.0;
  nss[21]=          pow(M_PI, 11.0) / 1814400.0;
  nss[22]= 4096.0 * pow(M_PI, 11.0) / 13749310575.0;
  nss[23]=          pow(M_PI, 12.0) / 19958400.0;
  nss[24]= 8192.0 * pow(M_PI, 12.0) / 316234143225.0;
  nss[25]=          pow(M_PI, 13.0) / 239500800.0;
  nss[26]=16384.0 * pow(M_PI, 13.0) / 7905853580625.0;

You see worse landings every year at Oshkosh.

A little hard and nose-first but at least he kept it on the ground and didn't bounce-bounce-crash.

This article seems to be about ML but good old fashioned brute force searches are also possible.

It's trivial to find formulas that fit data to within the variable's uncertainties. You can easily drown in such output. There are two main challenges with this approach: 1. make sure you have the right "ingredients" (factors) for the search, and 2. filter the output so that human reviewers don't waste time on obvious nonsense equations.

Filtering output is not terribly difficult. Some assessment of complexity is required and depending on the formula a symmetry score might be useful. Some actual physics equations are quite complex so you have to be expecting a simple equation or filtering output will be less effective.

Making sure you have all of the right potential factors available is very hard. Expanding the input factor set extends the search space and time.

Reminds me of this scene from War Games https://youtu.be/iRsycWRQrc8?t=66

> People can be addicted to ANYTHING that releases dopamine. And we are all doing it constantly in an unnatural way. > > This means that everything that triggers in you an excited, focused, joyful moment can be addicting.

Oh no, not this again. Dopamine isn't the thing that makes you feel euphoric, that comes from opioids.

https://www.psychologytoday.com/intl/blog/women-who-stray/20...

They're not as valuable as you might think. LL.com's go for >$1M but LL.org's and LL.net's are in the $10K-$50K range.

I missed registering kl.com by a few weeks and had to settle for kl.net. This was back 1995 when you had to email a template to Internic and wait about three weeks for a reply. In the template you had to provide working nameservers. I had put down some random hostnames for nameservers since I wasn't running my own yet and it was rejected after the usual three week delay. By the time I had nameservers set up a few weeks later a law firm had registered kl.com.

With working nameservers I was able to register maj.com (have since sold it) and finally kl.net which I plan to keep til I die.

Title would be less confusing if it said "were spied on"

I think it's common to experience this when taking on a significantly different role or being exposed to a new environment in your existing role (such as going to an industry conference for the first time). Your interactions with others are different than what you are used to and our brains are wired to bring that kind of novelty into sharp focus one way or another. It's an errant or exaggerated error signal.

Know that in time it will dissipate naturally as you gain experience and the new interactions become familiar. In the meantime don't let it affect your confidence in your work or others will pick up on that.

1. Consciously acknowledge it as a mental artifact and disregard it as such. Don't just ignore it but call it out in your mind as you feel it happening: "This is just imposter syndrome. I'm going to disregard those thoughts because it's not real and not helpful."

2. Strive for excellence in what you do.

3. Derive and project confidence from following step 2.

> Apple's strange hypermedia system

So it wasn't just me that thought it was an incredibly weird system...

I wondered why or even how anyone would actually use it.

There are several ways colorspace metadata can be included in a PNG.

- No colorspace metadata (software should assume sRGB)

- Built-in sRGB format chunk

- gAMA chunks

- cHRM chunks

- ICC profile chunks

IMO v4 ICC profiles are the modern and best way to encode colorspace info. The problem is not all software uses any or all of these.

ffmpeg for example decodes all of these chunks but does not actually use any of it. It even assumes by default PNGs are encoded with rec.701 gamma (common for legacy video). This is why PNG->x264 conversion with ffmpeg has weird colors unless you encode the PNGs with gamma ~2.0 instead of the sRGB standard ~2.2.

Color vision is much more complicated and “RGB” doesn’t work the way than most people think it does.

The spectral response of the L and M cones mostly overlaps and our perception of color relies heavily on “adversarial” transformations in the brain.

The result is a very different effective spectral response superficially resembling RGB bandpass filters except the red channel takes negative values (!) at some wavelengths:

https://en.m.wikipedia.org/wiki/CIE_1931_color_space

The negative values can be thought of as requiring additional anti-red (green+blue) to render the correct color.

The CIEXYZ color space was invented to address the negative values and also conveniently separate luminance from color information. It is widely used today to do color space transformations since it represents standard human color vision in a reasonably convenient and intuitive way.

On a side note, wide band RGB or Bayer filters used in digital cameras are a poor match for the CIE 1931 standard observer effective band pass filters (even ignoring the negative red values). They would result in low saturation colors if mapped directly to a full-gamut RGB colorspace. Conveniently or coincidentally they work well when directly mapped to a limited gamut sRGB color space. Narrower bandpass filters approximating the CIE1931 curves look correct when mapped to a wide gamut like rec.2020. The point is you cannot make simple assumptions about RGB colors at any point in the process.

The biggest problem we have today however is many systems are not aware of colorspaces and assume that RGB values are an absolute and invariant encoding of color.

This would be a disaster for startups and hobby sites hosting user-submitted content without a significant minimum size or revenue threshold.

It would definitely be the end for one of the sites I run (which received only one DMCA request in 22 years of operation).

iperf is the gold standard for measuring throughput but it requires a shell on both ends.

The default TCP mode is fairly intuitive and usually gives a good idea of what is going on.

For precise independent tests of up and down speeds you need to use UDP mode with increasing bit rates until you start to see significant packet loss in that direction. Repeat in the other direction.

Another consideration is that the endpoint you are testing from (probably some cloud vm or server at work) will likely have different routing to your other endpoint (home) than other sites/services you visit. It is not unusual for eyeball ISP's to sometimes have congested peering with specific networks in specific locations while your work->home path will be clean.

If you had to pick an inflection point where Sun's dominance in the Unix world began to decline it would be this.

Not in terms of total installations, momentum and exponential expansion of the entire industry distort that, but in terms of it's influence. This is also the exact same time that 386BSD/NetBSD/FreeBSD and Linux started releasing.

As others have pointed out BSD-based SunOS was the king of Unix-like operating systems in the late 80's to early 90's. Sys-V based Solaris (1992) was an immediate flop and quickly earned the nickname "Slowlaris". Only by version 2.4 was it even usable in production. By 2.6 it was a decent operating system but anyone who remembered using SunOS wished they had never switched.

Old Sears and JC Penny catalogs:

https://christmas.musetechnical.com/

Yes. We have a pretty good understanding of how neutrinos are created and destroyed and there should not be enough of them to explain the anomalous gravitation.

> Yes, dark matter is the best way we currently have for fitting the data

This is the key problem. Since there is no theory of what dark matter is made of or how it is created and destroyed, you can always have as much or as little of it as you need to fit the data.

As for gravity, we don't have anything close to a working theory of quantum gravity. We can't even measure the classical gravitational constant to more than about 4 digits. The reproducibility by different experiments has not demonstrably improved since the 1940's! Clearly there is a lot more we have to learn about gravity.

Reading through the documentation it looks like this emulates the legacy IOS model of announcing all BGP routes to neighbors by default unless there is a policy configured.

This outdated model has caused countless route leaks over the years. Any new or updated BGP implementations should require an explicit allow policy for any route advertisement to take place (at least to eBGP neighbors). IOS-XR and JunOS require explicit policies.

This is covered in RFC8212: https://datatracker.ietf.org/doc/html/rfc8212

BGP can be used for small things too.

Many enterprises use it for their connectivity. If you are multihomed it's basically essential.

Even if you are not multihomed BGP is the most robust way to handle failover between two uplinks to the same ISP. If you are not using full routes and just taking default from each ISP the requirements/load on your router(s) are almost nothing.

Another popular use case is inside private networks, especially over GRE tunnel meshes where the filtering features of BGP allow better/easier control over topology than OSPF.

I've even seen individual servers use BGP for anycasting (usually DNS servers) or http load balancing (with DSR and L4 hashing on the upstream router).

I don't think there are any 3090's with 128GB of ram however. If you need that much ultra high bandwidth ram the M1 Ultra is the only game in town.

The camera screenshots definitely looked worse but not terrible. Most of the time it will be compressed to hell for a videoconferencing app anyway.

A similar mistake can easily be made when using iperf to measure throughput or identify performance problems.

In TCP mode the results reflect a combination of forward and return path effects, though the return path usually has less effect on total throughput than forward path. Only with UDP mode can you accurately measure unidirectional path performance.

Those are called "diffraction spikes" https://en.wikipedia.org/wiki/Diffraction_spikes

They represent light that was diffracted by the edges of the hexagonal primary mirror segments and secondary mirror support struts.

The reason they are so prominent is because of how extremely overexposed the star is. Every star will have them but in a normally exposed star they are too faint to see.

In the Hubble Space Telescope you have four spikes that are just from the support struts of the secondary mirror. The circular mirror generates something called an Airy Disk https://en.wikipedia.org/wiki/Airy_disk.

Diffraction effects are unavoidable in any telescope and can tell you a lot about how well the telescope is working. In this case they indicate that Webb is aligned extremely well.

Back in January 2000 I set up an Atari 800 as a web server with a 3com CS-210 terminal server as the TCP interface.

The Atari had no problems keeping up with several requests per second even after being Slashdotted since all of the expensive TCP stuff was offloaded.

There was a 16-bit hit counter on the page that overflowed and the CS-210 would crash after a day or so but otherwise it worked surprisingly well.

https://kevinloch.com/atari/