Ganz entscheidend ist in dem Kontext den Beweis, dass es nicht schneller als mit Grover geht (und damit ein 256 Bit Schlüssel die Sicherheit eines 128 Bit Schlüssel liefert unter QC). Nicht nur weil alles andere ja weitreichende Implikationen bezgl. Berechenbarkeit hätte, sondern weil sonst durchaus denkbar wäre, dass USA/China/Russland bereits bessere Algorithmen bekannt sind, denn solche theoretischen Ergebnisse sind ja verhältnismäßig leicht zu realisieren (verglichen mit dem Bau eines QC) und damit ein Unsicherheitsfaktor gegeben wäre, falls man in 25-50 Jahren doch langsam in die Nähe von QC rückt.

As far as I am concerned, easy:
1. Print 16bn fantasy-money that ppl believe in
2. Buy/Trade BTC with that 16bn, let the price go up
3. Have people post-rationalize the rising price and let them draw lines in their charts and stuff and support news talking about 300k+ price and have nobody believe it will stop at around 20k
4. Sell everything you bought for around 20k within a month to the people who believe BTC goes to moon soon
5. Eventually market gets saturated and price goes down again, but now you are some billion USD richer

USDT market cap went up from 4bn to 20bn within 12 month.
I don't believe this is backed by USD.
What could be the reason to print that many Tether? As of now I tend to believe this was used to push the price up and collect money (current situation) by selling back at this higher price while people draw lines in charts believing they do something that is clever in 2020 or believe there is still a 'new 2017' event happening that will push bitcoin way beyond the ATH.

The price itself is irrelevant, but the volatility and long term stability of the price is important if Bitcoin aims to be used widely for payment purposes. If it provides low fees is very debatable, it is only suited to move large amounts of money as if people would start to buy bread with it, transaction fee would be way too high.
Current state of Bitcoin is desperate, it is used for high risk speculation mostly. Merchants accept Bitcoin more and more as it becomes cheaper to achieve this as payment providers include it but without price stability almost nobody will use Bitcoin itself for daily payments in the future.
However, as most people are committed to get wealthy by investing in Bitcoin, the incentive for price stability is very low, therefore price will continue to be volatile making Bitcoin a Ponzi-Scheme for the most part.

If an asset is known to be highly volatile you do not invest into it to store your value, people do not buy 1 BTC today and hope to receive the same purchasing power in 20 years, they buy 1 BTC because they believe the purchasing power of it will go 'to the moon' within the next 20 years.

When BTC price has stabilized for like 5 years, maybe it can then be used as store of value or as currency. Before that it will mainly be used as cash cow and high risk investment.

Schon der Begriff "Rechner" scheint mir stark irreführend zu sein.
Wenn ich 100 mal einen Apfel fallen lasse und messe, wie lange der braucht und davon den Durchschnitt berechne, dann habe ich zwar was 'gerechnet', aber keinen Gravitations-Rechner gebaut.

This has nothing to do with BTC, if I receive too much money from a company they will demand to get it returned. If I send too much money to a company they send it back to me. At least that's how things work in my country. A company refusing to do this is highly unprofessional. Your option may vary depending of where you live. If you gave money to a company that resides in a foreign country - bad for you, why did you even do that?
I would have the option to send a official request for money for which they have two weeks to react and can be escalated to a lawsuit which they know is gonna end with them paying everything, including my expenses.

Are there metrics to measure how much is Bitcoin used to buy stuff? I totally see why merchants tend to integrate BTC as a payment method, but in the end it's for now use as long as most people go crazy about the last ATH.

I see how Bitcoin can fill a nische and I believe it's mere existent is important, but I doubt it will ever get general relevance outside of the investment market.
I mean, who would even consider to sell Bitcoin to buy a new car, at the moment? Or even the daily coffee? [PS.: don't want to imply it's a bad time to sell bitcoin, but to demonstrate that bitcoin is not used as a store of value or even a currency that you just happen to have and use in your daily life]
You might use a system with a middle-man that changes your USD into BTC instantaneously to buy a coffee, but that negates any potential benefit of Bitcoin as well so you could just use your regular credit card.

I don't quite understand how Satoshi was very smart about the incentives to have Bitcoin work but didn't figure out that nobody is gonna use Bitcoin as a currency without a proper inflation mechanism. Even X+ years ago, people where telling 'at one point in time, all Bitcoins will be mined'. So for many years now, most people buy Bitcoin not to buy stuff with it but hope that more and more people will buy Bitcoin. Without a proper use case, this is not much more than a ponzi-scheme.

I really hope that in the end, Bitcoin and it's correlates will be more than a system to move money from normal people to scammers and "institional investors" (aka those professional scammers that brought us multiple economic crisis), but I fail to see that at the moment. They might just milk bitcoin until regulation successfully stops it and all that will be left is the idea of currencies owned by FANG vs. digital currencies owned by goverments to tighten the control of it's citizen.

Was ich aus Artikeln mitgenommen habe, wo Menschen berichten, welche als Ingenieure and QC (im Sinne des Threads hier) arbeiten:
Man weiß noch nicht einmal, ob wir QC überhaupt *jemals* haben werden. Es fehlt noch Jahrzehnte an Grundlagenforschung.

Gründe:
* Da die Qubits verschränkt werden müssen steigt der technologische Aufwand exponenziell. Wir haben noch keine Ahnung, wie wir eine größere Anzahl Qubits überhaupt beherrschen sollen
* Die Anzahl benötigter Qubits liegt in der Größenordnung Millionen. Bedenkt man, dass die Probleme exponenziell anwachsen mit der Anzahl der Qubits wird klar, wie unvorstellbar weit wir entfernt sind
* Der obige Punkt geht von logischen, fehlerkorrigierten Qubits aus. Qubits sind Fehleranfällig, deswegen muss man (soweit ich mich entsinne) mehrere tausend bis zehntausend physikalische Qubits zu einem einzelnen Qubit zusammenfassen
* Wir sind also noch nicht einmal in der lage, einen einzelnen fehlerfreien logischen Qubit zu erzeugen und benötigen aber einige Millionen davon. Nicht mehr zu unseren Lebzeiten, sorry.

* Die Forschung ist teuer. Teuer-teuer. Regierungen haben weder Man-power, Infrastruktur oder Geld um immer X Jahre vor Google oder IBM zu sein. Es wird keine super geheimen QC geben mit denen niemand rechnet.
* Jahre bevor es QC gibt kann man sehr simpel durch einen Hardfork bei BTC die Verfahren wechseln. Ich spiele hier Prophet und gehe schwer davon aus, dass man alte key-pairs, d.h. Adressen erst veralten und dann ungültig machen wird, d.h. alle Wallets/private keys welche nicht innerhalb von z.B. 5 Jahren transferiert werden werden ungültig werden. Man kann sich überlegen, welche stakeholder dafür bzw. dagegen wären.
* NIST standardisiert bereits QC-resistente Verfahren
* Der Rest der Welt ist weit träger als BTC, weder die Umstellung auf IPv6, DNSSEC oder irgendeine andere globale Technologie geht schnell voran. Krypto-Währungen werden in jedem Fall weit schneller sein als der Großteil der restlichen Welt von daher ist BTC prinzipbedingt weniger gefährdet.