The thread was started as a toot by a Mastodon user. All of the replies are actually Mastodon posts. Thanks to the magic of the Fediverse, these render in Lemmy as comments.

You can think about it this way. In relativity:

• You’re not allowed to have any way to determine an absolute speed. If your perceived acceleration were to vary (for a constant thrust) depending on your speed, that would give you a mechanism to determine absolute speed, but absolute speed doesn’t exist in relativity.
• Rather than “nothing can go faster than the speed of light,” given that we’ve just determined that absolute speed doesn’t exist, the next rule is instead: you are not allowed to observe anything travelling faster than the speed of light relative to you, and relativistic effects will ensure that this is so.

My main question, and the one that I initially came here to ask, is: if their ship continues applying the force that, under classical mechanics, was enough to accelerate them at 9.81 ms^-2, would the people inside still experience Earth-like artificial gravity, even though their velocity as measured by an observer is now increasing at less than that rate?

Relativity says yes. There’s no absolute speed, only relative speed; within the local reference frame of the ship, everything will continue to work normally, including the force experienced due to acceleration.

My understanding is that a trip taken at the speed of light would actually feel instantaneous to the traveller, while taking distance/speed of light to a stationary observer.

The ship is not actually going to reach the speed of light (as seen by an outside observer) though. The faster the ship goes, the more its (observed) mass increases, and the 9.8m/s² acceleration will have less and less of an effect. But to the people inside the ship, it appears as though they can accelerate indefinitely, going faster and faster at their steady rate of acceleration. Due to relativistic effects, it’ll never look like they are passing any objects outside the ship at more than the speed of light; instead it will appear as though the distance they have to travel is compressed, so they don’t have to travel as far.

you ever just spend over half an hour of your time researching a meme?

https://en.wikipedia.org/wiki/Killing_of_Timothy_Russell_and_Malissa_Williams – two homeless black people were pulled over for a traffic stop, they were not searched and were let go. As they departed, police claimed they heard shots fired from the vehicle as it passed them (later determined to be a backfire) prompting the beginning of a 22-mile police chase. When Russell eventually pulled into a parking lot, the pair were shot to death by thirteen officers who fired 137 shots at the pair. It’s unclear where the pizza comes into it, but police alleged they saw a firearm in the vehicle (none was found).

Mark Venuti: https://wc.arizona.edu/papers/94/108/01_92_m.html – allegedly suicide-by-cop, he was carrying a Bible over his head and after being shot, charged at the officers yelling at them to shoot him again.

Khiel Coppin: https://www.courthousenews.com/brooklyn-mom-of-2-sons-killed-by-police-sues/ – Khiel was mentally ill and allegedly told police he had a gun. Police later also killed his brother in a separate altercation, in apparent retaliation for bad press over the killing of Khiel.

https://en.wikipedia.org/wiki/Killing_of_Douglas_Zerby – a neighbour mistook the hose nozzle for a gun and called police; officers did not check what he was holding and fired without warning, killing him.

Levar Jones: https://www.11alive.com/article/news/ex-sc-officer-sentenced-for-shooting-man-tells-him-i-screwed-up/101-464504897 – Levar, a black man, was shot and wounded by an officer at a traffic stop while retrieving his licence from his vehicle. His dashcam captured the entire incident. The officer was convicted of aggravated assault and battery and imprisoned for five years, and Levar received a $285,000 settlement.

https://en.wikipedia.org/wiki/Killing_of_John_Crawford_III – shot and killed while holding a BB gun, captured on surveillance footage. A second person suffered a fatal heart attack while fleeing from the shooting.

David Loveless: http://www.policebrutality.info/2012/04/man-arrested-for-pointing-finger-at-cops.html – Arrested and charged with two counts of “assault on a law enforcement officer by intimidation” for allegedly pointing his finger like a gun at officers. David denied pointing his fingers at anyone. The officers involved had previously testified against David’s son in a robbery case, giving him motive to threaten them. I can’t find further information on whether David was convicted of these charges.

Rumain Brisbon: https://www.dangerousobjects.org/rumain-brisbon (link includes sources) – Note: This site catalogues multiple examples of unarmed black people being subject to shooting or police brutality, with a focus on the harmless objects that were the catalyst of the police response.

https://en.wikipedia.org/wiki/Shooting_of_Charles_Kinsey – Charles, a behavioral therapist, was retrieving his autistic patient Arnaldo Rios-Soto who had run away from a group home, when police encountered them during an unrelated search for an armed suicidal man. Arnaldo naturally did not respond to police orders. Kinsey, while lying on the ground with his hands in the air and attempting to negotiate between police and his patient, was shot when officer Jonathan Aledda mistook the toy truck Arnaldo held to be a gun – interestingly, Jonathan says he was aiming at Arnaldo, who he thought was holding Charles hostage, but shot Charles instead. Jonathan was arrested in 2017 and found guilty of culpable negligence in 2019, at which point he was fired, but his conviction was overturned in 2022.