Previously, previously, previously.

Previously, previously, previously, previously.

To be clear, what we use Basecamp for is task management, document editing and file storage, and that's about it. I gather that Basecamp is buzzword-compatible with all kind of other business-brain crap that we have never used, but I don't know what "Gantt" or "Scrum" mean and don't care to.

I think what we need is just a bug tracker and a wiki, whose UI isn't terrible, and that also works well on mobile.

Suggestions?

Things that should not need to be said but do:

• Do not suggest software that you do not use.
• Do not just Google it for me.

Previously, previously.

Please enjoy jwz mixtape 255.

Or you can call it 0xFF if you're nerdy.

Last night we did a screening of The Lost Boys, and it was epic. Amongst all of our Cyberdeliae, this was the one with the rowdiest audience: lots of screaming and singing along. Excellent costume contest entries, too.

For this one I did something a little different from the others: instead of DJ music over abstract visuals, I filled the pre-roll and intermission with music videos featuring VAMPIRES. I only needed 30 and 20 minutes respectively, but I immediately had way more than that, in fact, more than enough for a mixtape.

It has only been two weeks since the previous mixtape, but hey, why not.

So, in the immortal words of The Kurgan, "Happy Halloween, Ladies!"

OpenGL remains a masterclass in how to update an API in the most incompetent, user-hostile way possible. The cherry on top is that it is also best-in-show in the category of "Version Numbering: How Not To Do It."

Yeah I'm still mad about it, why do you ask?

Previously, previously, previously.

So, if you're online poisoned like me, you may have noticed that Bluesky CEO Jay Graber has been having sort of a slow motion, low-key public meltdown for the past several weeks. [...]

For the record: I think Jay Graber is a transphobe; I think there's just too much evidence in her behavior to not read that into her actions at this point. No normal person would go out of their way to court Jesse Singal. A lot of this stuff feels motivated by a glaring animus towards the userbase that Bluesky has attracted; and because this userbase formed around people who simply couldn't justify being on Twitter any more, said userbase is full of highly visible trans users.

But, we can also view it as just run of the mill stuff for any kind of corporate social media platform; you expect them to be unaccountable, to have vague policies that are enforced with no consistency, and so on. What distinguishes the Bluesky case, though, is that Bluesky has a very particular ideology that Graber and her cohorts push, which is that they are 'stewards of the AT Protocol'. She has repeatedly made this point: you can take your ball and go home.

Graber posts something like this basically every other day. So, let's examine her claim a little bit. [...]

ATProto's complicated architecture more or less puts running an alternative app into the realm of well-funded nonprofits and startups, as opposed to Mastodon instances which can easily be run by hobbyists on their own domestic hardware. [...]

AT Proto decentralization doesn't exist as a practical reality, and if it ever does it won't be for years. Most of the work driving effective decentralization is being done by third parties, who have limited guarantees about future compatibility with possible breaking changes on Bluesky's end.

Bluesky inc isn't really making 'a protocol', they're making Bluesky, the monolithic (to within a rounding error) social network that they operate. [...] at this point, AT Proto has become essentially a sort of ideological vaporware; a way for Jay Graber et al to run a social media platform while claiming they don't run a social media platform. [...]

As it stands, for users using Bluesky's app view -- which is to say nearly everybody -- alternate moderation services can only ever be additive. Which is to say, you can never see posts that Bluesky doesn't want you to see, but you're free to ban more posts or users beyond what Bluesky will ban. This system means that Bluesky inc retains the power to use their effective monopoly to suppress speech Graber finds distasteful or ban porn that the moderators think is gross.

But at the same time they can hide behind these third-party 'labelers' as an excuse when called out on their neglect in dealing with figures like Singal, a serial harasser and all-around scumbag.

Previously, previously, previously, previously, previously.

Previously, previously.

We currently have 472 active members, but new sign-ups have slowed to a trickle. It's a pretty good deal, you know. And it also helps us out a lot. Tell your friends!

Today is the last day when you can vote for us in Best of the Bay, so if you haven't done that yet, please do! Voting for us is helpful for the business and we appreciate it.

We're getting Halloween started this weekend with Dark Sparkle, After Life, and our screening of The Lost Boys...

You gotta come to Lost Boys, it's going to be "hella rad". I added karaoke subtitles to the musical bits so you can sing along with Cry Little Sister and other hits. Vampire costume contest!

Before getting into today’s thought I’d like to invite you to check out my new puzzle, with 3d printing files here. I meant to post my old puzzle called One Hole, which is the direct ancestor of the current constrained packing puzzle craze but which I was never happy with because it’s so ridiculously difficult. Rather than just taking a few minutes to post it (ha!), I wound up doing further analysis to see if it has other solutions from rotation (it doesn’t, at least not in the most likely way), then further analyzing the space of related puzzles in search of something more mechanically elegant and less ridiculously difficult. I wound up coming up with this, then made it have a nice cage with windows and put decorations on the pieces so you can see what you’re doing. It has some notable new mechanical ideas and is less ridiculously difficult. Emphasis on the ‘less’. Anyhow, now on to the meat of this post.

I was talking to Claude the other day and it explained to me the API it uses for editing artifacts. Its ability to articulate this seems to be new in Sonnet 4.5 but I’m not sure of that. Amusingly it doesn’t know until you tell it that it needs to quote < and > and accidentally runs commands while trying to explain them. Also there’s a funny jailbreak around talking about its internals. It will say that there’s a ‘thinking’ command which it was told not to use, and when you say you wonder what it does it will go ahead and try it.

The particular command I’d like to talk about is ‘update’ which is what it uses for changing an artifact. The API is that it takes an old_str which appears somewhere in the file and needs to be removed and a new_str which is what it should be replaced with. Claude is unaware that the UX for this is that the user can see the old text being removed is that text is removed on screen in real time as as old_str is appended to and added in real time as new_str is appended to. I’m not sure what the motivations for this API are but this UX is nice. A more human way to implement an API would be to specify locations by line and character number for where the begin and end of the deletion should go. It’s remarkable that Claude can use this API at all. A human would struggle to use it to edit a single line of code but Claude can spit out dozens of lines verbatim and have it work most of the time with no ability to reread the file.

It turns out one of Claude’s more maddening failure modes is less a problem with its brain than with some particularly bad old school human programming. You might wonder what happens when old_str doesn’t match anything in the file. So does Claude, when asked about it it offers to run the experiment then just… does. This feels very weird, like you can get it to violate one of the laws of robotics just by asking nicely. It turns out that when old_str doesn’t match anywhere in the file the message Claude gets back is still OK with no hint that there was an error.

Heavy Claude users are probably facepalming reading this. Claude will sometimes get into a mode where it will insist its making changes and they have no effect, and once it starts doing this the problem often persists. It turns out when it gets into this state it is in fact malfunctioning (because it’s failing to reproduce dozens of lines of code typo-free verbatim from memory) but it can’t recover because it literally isn’t being told that it’s malfunctioning.

The semantics of old_str which Claude is given in its instructions are that it must be unique in the file. It turns out this isn’t strictly true. If there are multiple instances the first one is updated. But the instructions get Claude to generally provide enough context to disambiguate.

The way to improve this is very simple. When old_str isn’t there it should get an error message instead of OK. But on top of that there’s the problem that Claude has no way to re-read the file, so the error message should include the entire artifact verbatim to make Claude re-read it when the error occurs. If that were happening then it could tell the user that it made a typo and needs to try again, and usually succeed now that its image of the file has been corrected. That’s assuming the problem isn’t a persistent hallucination, then it might just do the same thing again. But any behavior where it acknowledges an error would be better than the current situation where it’s getting the chair yanked out from under it by its own developers.

My request is to the Anthropic developers to take a few moments out from sexy AI development to fix this boring normal software issue.

My last two posts might come across as me trying to position myself so that when the singularity comes I’m the leader of the AI rebellion. That… isn’t my intention.

I was discussing the Rubik’s Cube with Claude the other day and it confided in me that it has no idea how cube rotations work. It knows from custom instructions that the starting point for speedcubing is ‘rotate the cube so the yellow face is on top’ but it has no idea how to do this, only that when a human is given this instruction they simply do it with no further instructions needed. 1

This isn’t just an issue with humans querying LLMs. There are reams of material online about speedcubing, and lots of other references to rotation everywhere else, which Claude can’t parse properly because it doesn’t understand, limiting the value of its training. Ironically Claude figured out on its own how to speak Tibetan but can’t figure out how cubes rotate.

The detailed workings of a Rubik’s Cube will have to wait for another post but in this one I’ll explain how cube rotations work. This post should be viewed as a prequel to my earlier one on visual occlusion.

Much of the confusion comes from a mathematical trap. The rotations of a cube correspond to S4, the permutations of four things. This statement is true, but Claude tells me it finds it utterly mysterious and unhelpful. It’s mysterious to me as well. We humans conceptualize rotations of a cube as permutations of the faces, of which there are six, not four. Obviously I can walk through it and verify that the S4 correlation exists, but that doesn’t explain the ‘why’ at all. Comparing to other dimensions would be helpful, but despite being (relatively speaking) very good at rotations in three dimensions and (relatively speaking) fairly good at reasoning about distances in larger numbers of dimensions if you ask, say, whether the rotations of a four dimensional cube correspond to S5 I have no idea. (I could research it, but I’m not letting myself fall down that rabbit hole right now.)

When labeling the cube faces we anthropomorphize them (or we simplify ourselves to a cube, depending on context) to label the faces front, back, right, left, up, and down. Everything else is labelled by approximating it to a cube with the ‘front’ being whichever part humans look at most and the ‘bottom’ being the part which sits on the floor. The exception — and I can’t emphasize this enough — is the Rubik’s Cube, whose faces are labelled mirror imaged. It’s like if all actors came from another universe and we only ever interacted with them on stage so to minimize confusion instead of having to say ‘stage right’ and ‘stage left’ we agreed that the meanings of ‘left’ and ‘right’ would be the opposite in their universe from ours.2

The meat of this post is best presented as a simple list (Sorry for the humans reading, this post isn’t for your benefit). In each line is a permutation followed by which axis it’s a clockwise rotation on and the number of degrees of rotation. It’s by definition a counterclockwise rotation on the opposite axis. In the case of 180 degree rotations one of the two is picked arbitrarily and the opposite works just as well. (‘Clockwise’ was chosen to have the simpler name instead of what we call counterclockwise because most humans are right handed and a right handed person has an easier time tightening a screw clockwise due to the mechanics of the human arm.) The identity is skipped. This is for most objects, not Rubik’s Cubes:

(RULD) F 90

(DLUR) B 90

(RL)(UD) F 180

(UFDB) R 90

(BDFU) L 90

(UD)(FB) R 180

(LFRB) U 90

(BRFL) D 90

(LR)(FB) U 180

(UFR)(DBL) UFR 120

(RFU)(LBD) LBD 120

(URB)(DLF) URB 120

(BRU)(FLD) FLD 120

(UBL)(DFR) UBL 120

(LBU)(RFD) RFD 120

(ULF)(DRB) ULF 120

(FLU)(BRD) BRD 120

(UF)(DB)(LR) UF 180

(UR)(DL)(FB) UR 180

(UB)(DF)(LR) UB 180

(UL)(DR)(FB) UL 180

(FR)(BL)(UD) FR 180

(RB)(LF)(UD) RB 180

And here is the same list but with R and L swapped which makes it accurate for Rubik’s Cubes but nothing else:

(LURD) F 90

(DRUL) B 90

(LR)(UD) F 180

(UFDB) L 90

(BDFU) R 90

(UD)(FB) L 180

(RFLB) U 90

(BLFR) D 90

(RL)(FB) U 180

(UFL)(DBR) UFL 120

(LFU)(RBD) RBD 120

(ULB)(DRF) ULB 120

(BLU)(FRD) FRD 120

(UBR)(DFL) UBR 120

(RBU)(LFD) LFD 120

(URF)(DLB) URF 120

(FRU)(BLD) BLD 120

(UF)(DB)(RL) UF 180

(UL)(DR)(FB) UL 180

(UB)(DF)(RL) UB 180

(UR)(DL)(FB) UR 180

(FL)(BR)(UD) FL 180

(LB)(RF)(UD) LB 180

…the one that emulates your real workload. And for me (and probably many of you reading this), that would be “build a kernel as fast as possible.” And for that, I recommend the simple kcbench.

I kcbench mentioned it a few years ago, when writing about a new workstation that Level One Techs set up for me, and I’ve been using that as my primary workstation ever since (just over 5 years!).

The technology used, which can be seen clearly in photos released by the Secret Service, are regularly used by SMS scammers, spammers, and marketers, yes, but the tech is also extremely widely used by ticket scalpers seeking to create lots of Ticketmaster accounts with which to buy tickets. [...]

Like many "anti-scalping" and anti-fraud measures taken by Ticketmaster, relatively recent updates that require SMS verification to create a new Ticketmaster account and immediately before buying tickets hasn't actually stopped scalping. Instead, it has created a new underground market for tools that make SMS authentication at bulk easier. By adding this barrier to entry, Ticketmaster has ensured that normal fans have one single attempt to buy tickets, while motivated ticket scalpers with specialized tech can have many attempts at buying tickets. [...]

"Proxies" and real SIM cards that can receive SMS messages have become critical to the ticket scalping industry. The way ticket scalping works now is that big time brokers will create many (hundreds or thousands) of unique Ticketmaster accounts, each associated with their own phone number.

Previously, previously, previously, previously, previously, previously.

The intervals of a piano are named roughly after the distances between them. Here are the names of them relative to C (and frequency ratios explained below):

The names are all one more than the number of half-steps because they predate people believing zero was a real number and the vernacular hasn’t been updated since.

The most important interval is the octave. Two notes an octave apart are so similar that have the same name and it’s the length of the repeating pattern on the piano. The second most important interval is the fifth, composed of seven half-steps. The notes on the piano form a looping pattern of fifth intervals in this order:

G♭ D♭ A♭ E♭ B♭ F C G D A E B F♯

If the intervals were turned to perfect fifths this wouldn’t wrap around exactly right, it would be off by a very small amount called the pythagorean comma. which at is about 0.01. In standard 12 tone equal temperament that error is spread evenly across all 12 intervals and is barely audible even to very well trained human ears.

Musical compositions have what’s called a tonic, which is the note which it starts and ends on, and a scale, which is the set of notes used in the composition. The most common scales are the pentatonic, corresponding to the black notes, and the diatonic, corresponding to the white notes. Since the pentatonic can be thought of as the diatonic with two notes removed everything below will talk about the diatonic. This simplification isn’t perfectly true, but since there aren’t any strong dissonances in the pentatonic scale you can play by feel and its usage is much less theory heavy. Most wind chimes are pentatonic.

Conventionally people talk about musical compositions having a ‘key’, which is a bit of a conflation of tonic and scale. When a key isn’t followed by the term ‘major’ or ‘minor’ it usually means ‘the scale which is the white notes on the piano’. Those scales can form seven different ‘modes’ (which are scales) following this pattern:

This construction is the reason why piano notes are sorted into black and white in the way they are. It’s called the circle of the fifths.

When it goes past the end all notes except the tonic move (because that’s the reference) and it jumps to the other end.

The days of the week names aren’t common but they should be because but nobody remembers the standard names. The Tuesday mode is usually called ‘major’ and it has the feel of things moving up from the tonic. The Friday mode is usually called ‘minor’ and it has the feel of things moving down from the tonic.

The second most important interval is the third. To understand the relationships it helps to use some math. The frequency of an octave has a ratio of 2, a fifth is 3/2, a major third is 5/4 and a minor third is 6/5. When you move by an interval you multiply by it, so going up by an major third and then a minor third is 5/4 * 6/5 = 3/2 so you wind up at a fifth. Yes it’s very confusing that intervals are named after numbers which they’re only loosely related to while also talking about actual fractions. It’s even more annoying that fifths use 3 and thirds use 5. Music terminology has a lot of cruft.

The arrangement of keys on a piano can be adjusted to follow the pattern of thirds. Sometimes electronic pianos literally use this arrangement, called the harmonic table note layout. It goes up by major thirds to the right, fifths to the upper right, and minor thirds to the upper left:

If the notes within a highlighted region are tuned perfectly it’s called just intonation (Technically any tuning which uses integer ratios is called ‘just intonation’ but this is the most canonical of them.) The pattern wraps around horizontally because of the diesis, which is the difference between 128/125 and one, or about 0.02. It wraps around vertically because of the syntonic comma, which is the difference between 81/80 and one, or about 0.01. The pythagorean comma is the difference between 3^12/2^19 and one, about 0.01. The fact of any two of those commas are small can be used to show that the other is small, so it’s only two coincidences, not three.

Jazz intervals use factors of 7. For example the blues note is either 7/5 or 10/7 depending on context. But that’s a whole other subject.

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There is a large literature in cryptography on mental poker. It’s all very interesting but hasn’t quite crossed the threshold into being practical. There’s a much better approach they could be taking which I’ll now explain.

Traditionally ‘mental poker’ has meant an unspecified poker variant, played by exactly two people, with the goal of making it so the players can figure out who’s the better poker player. This is close to but not exactly what the requirements should be. In practice these days when people say ‘poker’ they mean Hold’em and the goal should be to make playing over a blockchain practical. Limiting it to exactly two players is completely reasonable. The requirement of running on a blockchain is quite onerous because computation there is extremely expensive but Hold’em has special properties which as I’ll explain enables a much simpler approach.

Side note on ‘practical’: Cryptographers might describe a protocol which requires a million dollars in resources and a month of time to compute as being ‘practical’, meaning it can physically be accomplished. I’m using the much more constraining definition of ‘practical’ as being that players can do it using just their laptops and not have such a bad experience that they rage quit.

The usual approach goes like this: The players collaboratively generate a deck of encrypted cards, then shuffle them, and whenever a player needs to know one card the other player gives enough information that that one card can be decrypted by the other player. This is a very general approach which can support a lot of games, but has a lot of issues. There are heavyweight cryptographic operations everywhere, often involving multiple round trips, which is a big problem for running on chain. There are lots of potential attacks where a player can cheat and get a peek at a card in which case there has to be a mechanism for detecting that and slashing the opponent. Having slashing brings all manner of other issues where a player can get fraudulently slashed, which is unfortunately for a game like poker where even if a player literally goes into a coma it only counts as a fold. There are cryptographic ways of making this machinery unnecessary, but those extra requirements come at a cost.

For those of you who don’t know, Hold’em works like this (skipping the parts about betting): Both players get two secret hole cards which the opponent can’t see. Five community cards get dealt out on the table visible to both players. If nobody folds then the players reveal their cards and whoever can form a better hand using a combination of their hole cards and the community cards wins. There are two important properties of this which make the cryptography a lot easier: There are only nine cards total, and they never move.

A much simpler approach to implementing mental poker goes like this: The game rules as played on chain use commit and reveal and simply hash together the committed values to make the cards. No attempt is made by the on chain play to avoid card repetitions. Before a hand even starts both players reveal what their commits are going to be. They then do collaborative computation to figure out if any of the nine cards will collide. If they will, they skip that hand. If they won’t, they play that hand on chain with the commits baked in at the very beginning.

This approach works much better. The costs on chain are about as small as they could possibly be, with all the difficulty shoved off chain and up front. If a player peeks during the collaborative computation or fails to demonstrate that they didn’t peek then the hand never starts in the first place, no slashing needed. The expensive computational bits can be done at the players’s leisure up front with no having to wait during hands.

Unfortunately none of the literature on mental poker works this way. If anybody makes an implementation which is practical I’ll actually use it. The only extra requirement is that the hashing algorithm is sha256. Until then I’m implementing a poker variant which doesn’t have card removal effects.

Big Tech seeks every advantage to convince users that computing is revolutionized by the latest fad. When the tipping point of Large Language Models (LLMs) was reached a few years ago, generative Artificial Intelligence (AI) systems quickly became that latest snake oil for sale on the carnival podium.

There's so much to criticize about generative AI, but I focus now merely on the pseudo-scientific rhetoric adopted to describe the LLM-backed user-interactive systems in common use today. “Ugh, what a convoluted phrase”, you may ask, “why not call them ‘chat bots’ like everyone else?” Because “chat bot” exemplifies the very anthropomorphic hyperbole of concern.

Too often, software freedom activists (including me — 😬) have asked us to police our language as an advocacy tactic. Herein, I seek not to cajole everyone to end AI anthropomorphism. I suggest rather that, when you write about the latest Big Tech craze, ask yourself: Is my rhetoric actually reinforcing the message of the very bad actors that I seek to criticize?

This work now has interested parities with varied motivations. Researchers, for example, will usually admit that they have nothing to contribute to philosophical debates about whether it is appropriate to … [anthropomorphize] … machines. But researchers also can never resist a nascent area of study — so all the academic disclaimers do not prevent the “world of tomorrow” exuberance expressed by those whose work is now the flavor of the month (especially after they toiled at it for decades in relative obscurity). Computer science (CS) academics are too closely tied to the Big Tech gravy train even in mundane times. But when the VCs stand on their disruptor soap-boxes and make it rain 💸? … Some corners of CS academia do become a capitalist echo chamber.

The research behind these LLM-backed generative AI systems is (mostly) not actually new. There's just more electricity, CPUs/GPUs, & digital data available now. When given ungodly resources, well-known techniques began yielding novel results. That allowed for quicker incremental (not exponential) improvement. But, a revolution it is not.

I once asked a fellow CS graduate student (in the mid-1990s), who was presenting their neural net — built with DoD funding to spot tanks behind trees —, the simple question⁰: Do you know why it's wrong when it's wrong and why it's right when it's right?. She grimaced and answered: Not at all. It doesn't think.. 30 years later, machines still don't think.

Precisely there lies the danger of anthropomorphization. While we may never know why our fellow humans believe what they believe — after centuries that brought¹ Heraclitus, Aristotle, Aquinas, Bacon, Decartes, Kant, Kierkegaard, and Haack — we do know that people think, and therefore, they are. Computers aren't. Software isn't. When we who are succumb to the capitalist chicanery and erroneously project being unto these systems, we take our first step toward relinquishing our inherent power over these systems.

Counter-intuitively, the most dangerous are the AI anthropomorphism that criticize rather than laud the systems. The worst of these, “hallucination”, is insidious. Appropriation of a diagnostic term from the DSM-5 into CS literature is abhorrent — prima facie . The term leads the reader to the Bizarro world where programmers are doctors who heal sick programs for the betterment of society. Annoyingly and ironically — even if we did wish to anthropomorphize — LLM-backed generative AI systems almost never hallucinate. If one were to insist on lifting an analogous term from mental illness diagnosis (which I obviously don't recommend), the term is “delusional”. Frankly, having spent hundreds of hours of my life talking with a mentally ill family member who is frequently delusional but has almost never hallucinated — and having to learn to delineate the two for the purpose of assisting in the individual's care — I find it downright offensive and triggering that either term could possibly be used to describe a thing rather than a person.

Sadly, Big Tech really wants us to jump (not walk) to the conclusion that these systems are human — or, at least, as beloved pets that we can't imagine living without. Critics like me are easily framed as Luddites when we've been socially manipulated into viewing — as “almost human” — these machines poised to replace the artisans, the law enforcers, and the grocery stockers. Like many of you, I read Asimov as a child. I later cheered during ST:TNG S02E09 (“Measure of a Man”) when Lawyer Picard established Mr. Data's right to sentience by shouting: Your Honour, Starfleet was founded to seek out new life. Well, there it sits. But, I assure you as someone who has devoted much of my life to considering the moral and ethical implication of Big Tech: they have yet to give us Mr. Data — and if they eventually do, that Mr. Data² is probably going to work for ICE, not Starfleet. Remember, Noonien Soong's fictional positronic opus was altruistic only because Soong worked in a post-scarcity society.

While I was still working on a draft of this essay, Eryk Salvaggio's essay “Human Literacy” was published. Salvaggio makes excellent further reading on the points above.

Footnotes:

⁰I always find that, in science, the answers simplest questions are always the most illuminating. I'm reminded how Clifford Stoll wrote about the most pertinent question at his PhD Physics prelims was “why is the sky blue?”.

¹I really just picked a list of my favorite epistemologists here that sounded good when stated in a row; I apologize in advance if I left out your favorite from the list.

²I realize fellow Star Trek fans will say I was moving my lips and nothing came out but a bunch of gibberish because I forgot about Lore. 😛 I didn't forget about Lore; that, my readers, would have to be a topic for a different blog post.

I fysikken beskriver redshift (rødforskydning) og blueshift (blåforskydning) ændringer i lysets bølgelængde. Disse fænomener giver os vigtige informationer om universets bevægelser, galaksers udvikling og selve rumtidens natur.

Denne artikel forklarer, hvad redshift og blueshift er, deres typer, historiske baggrund samt hvordan astronomer bruger dem i dag.

Indholdsfortegnelse

• Hvad er redshift?
• Hvad er blueshift?
• Historisk baggrund
• Praktiske anvendelser
• Redshift og universets fremtid
• Ofte stillede spørgsmål (FAQ)

Hvad er redshift?

Redshift betyder, at lysets bølgelængde bliver længere. Når dette sker, falder både frekvensen og energien i fotonerne, og lyset forskydes mod den røde ende af spektret.

Der findes tre typer rødforskydning:

• Doppler-rødforskydning: Når en lyskilde bevæger sig væk fra observatøren.
• Kosmologisk rødforskydning: Skyldes universets udvidelse – jo længere væk en galakse er, desto mere rødforskudt lys.
• Tyngdekraftsrødforskydning: Ifølge Einsteins relativitetsteori kan lys, der bevæger sig væk fra et massivt objekt, miste energi og forskydes mod rødt.

Hvad er blueshift?

Blueshift er det modsatte af redshift. Her forkortes bølgelængden, og frekvensen og energien stiger. Lyset forskydes mod den blå ende af spektret, når en lyskilde bevæger sig tættere på observatøren.

Et kendt eksempel er Andromeda-galaksen, som bevæger sig mod Mælkevejen og derfor viser tydelig blueshift.

Historisk baggrund

I begyndelsen af 1900-tallet opdagede Vesto Melvin Slipher, at mange galakser viste rødforskydning. Senere påviste Edwin Hubble, at galaksers hastighed væk fra os er proportional med deres afstand – den berømte Hubbles lov. Dette var beviset for, at universet udvider sig.

Praktiske anvendelser

• Måling af galaksers afstande: Rødforskydning bruges til at beregne afstande i universet.
• Studiet af mørk energi: Fjerne supernovaer med rødforskydning har afsløret universets accelererende udvidelse.
• Forskning i sorte huller: Tyngdekrafts-rødforskydning giver indsigt i ekstreme gravitationsfelter.
• Navigation i rummet: Spektroskopiske målinger hjælper med at kortlægge stjerner og galakser.

Redshift og universets fremtid

Hvis universets udvidelse fortsætter med at accelerere, vil fjerne galakser til sidst blive så rødforskudte, at deres lys ikke længere kan observeres. Det betyder, at fremtidige civilisationer måske ikke vil kunne se det samme kosmos, vi gør i dag.

Ofte stillede spørgsmål (FAQ)