A delightful quirk of relativity theory • Hacker News Board

Re: A delightful quirk of relativity theory

#81

Post by actually_a_dog » Tue, Jan 18, 2022, 3:05 PM UTC

bradstewart wrote: post #76

Thomashuet wrote: post #7

More readable formatting: https://threadreaderapp.com/thread/1482811504424542211.html

Am I crazy, in that I actually like Twitter threads for this sort of thing--at least in the hands of a capable author? When threaded correctly (as this one is), its easy to follow. And the requirement to condense and split thoughts into tweet-sized chunks creates natural breaks to pause and consider the content before continuing. I find the cadence of "each thought is a tweet" provides a nice rhythm. Sure, you can do…

You may actually have something there. The average word length in English is approximately 5 letters, which gives you an average of about 56 words per tweet. That's roughly 5-6 solid sentences, which is... one good paragraph. It probably didn't work as well before they raised the character limit from 140 to 280.

Re: A delightful quirk of relativity theory

#82

Post by vidarh » Tue, Jan 18, 2022, 3:05 PM UTC

kybernetikos wrote: post #66

vidarh wrote: post #53

Earlier quoted context omitted.

"Unpredictable" is imprecise to the point of being meaningless. If a black box is fully deterministic to the point that you can construct a model that is entirely accurate, then there's nothing "free" about it. What you're modelling has no agency. For the notion of "free will" to have any meaning at all, it doesn't need to be "unpredictable" in the sense that it keeps confounding someone trying to predict it all the…

> What you're modelling has no agency I see no reason to think that just because something is predictable it is not free. That seems like such a strange constraint to me that I can only assume that we have different understandings of what it means to be free. If I know someone well, I might predict that when offered a free choice between an ice cream and a brussels sprout they will choose the ice cream. The fact that…

Given the same starting state, either you get the same outcome every time, or there's randomness involved, that is the point.

I challenge you to describe a selection process that is not fully deterministic but where the lack of determinism is caused by something other than randomness.

That is what you need to be able to come up with to define free will in a way that isn't smoke and mirrors.

There's no agency. Nothing but automatons.

Re: A delightful quirk of relativity theory

#83

Post by philipov » Tue, Jan 18, 2022, 3:05 PM UTC

irthomasthomas wrote: post #21

This would be more fun in a blog post. Twitter is a fucking horrible format for a complex analysis of special relativity. That aside, my favourite quirk from relativity is this: "The more you move in space, the less you move in time." Like relativity in general, it sounds simple enough, but it's consequences are profoundly shocking. (That is, if you take the time to understand it, and don't leap to the conclusion tha…

There is no room for free will in physics, period. All processes are completely deterministic. Even quantum processes might appear to be probabilistic if you look at individual particles, but the statistics are nevertheless completely deterministic: if you look at enough particles, a predictable shape will emerge. The future is set in stone and not only is there no way to change it, but the concept of changing the future doesn't even make sense.

Free will is not something that exists in nature, it is something that exists in the psychology of agents with limited information about the world they operate in. Attempting to find a physical basis for free will is like trying to use an optical drive to read data off a pancake.

Re: A delightful quirk of relativity theory

#84

Post by destitude » Tue, Jan 18, 2022, 3:07 PM UTC

irthomasthomas wrote: post #21

This would be more fun in a blog post. Twitter is a fucking horrible format for a complex analysis of special relativity. That aside, my favourite quirk from relativity is this: "The more you move in space, the less you move in time." Like relativity in general, it sounds simple enough, but it's consequences are profoundly shocking. (That is, if you take the time to understand it, and don't leap to the conclusion tha…

I was going to post this exact comment. I gave up following the twitter thread because it was so annoying.

Re: A delightful quirk of relativity theory

#85

Post by jahnu » Tue, Jan 18, 2022, 3:09 PM UTC

ctw wrote: post #51

jahnu wrote: post #43

Earlier quoted context omitted.

> "The more you move in space, the less you move in time." Isn't that missing a bit at the end? The less you appear to move in time from a different frame of reference? We all move through time at exactly 1 second per second, don't we? For reference: Here's Sean Carrol saying exactly that (but in reply to a different question) https://www.preposterousuniverse.com/podcast/2021/12/15/ama-... "...it always goes by one s…

Disclaimer: I’m interested in relativity and have been reading about it lately but I’m no authority. > We all move through time at one second per second, don’t we? You need to define “move through time”. The only way to measure time is with a clock, and the clock’s motion relative to you affects the measurement. If you let everyone define “time” as the thing measured by the watch on their wrist, then everyone moves t…

That's my understanding too but I am also saying that "less you move in time" needs to be more rigorously defined. As it stands above I'm not sure it makes sense, even though it might be a useful fiction to get a handle on the weirdness of it all.

I'm also no authority whatsoever on the topic :)

Re: A delightful quirk of relativity theory

#86

Post by Jeff_Brown » Tue, Jan 18, 2022, 3:10 PM UTC

awb wrote: post #61

irthomasthomas wrote: post #21

This would be more fun in a blog post. Twitter is a fucking horrible format for a complex analysis of special relativity. That aside, my favourite quirk from relativity is this: "The more you move in space, the less you move in time." Like relativity in general, it sounds simple enough, but it's consequences are profoundly shocking. (That is, if you take the time to understand it, and don't leap to the conclusion tha…

> Take the case of two people on Earth, one stationary and one travelling past in a car. They each have a different reference frame, and a different set events which make up their present. Now imagine that there is an alien government in Andromeda debating a possible invasion of Earth. In the reference frame of the person on Earth who is moving, the debate is still going on. But, in the reference frame of the station…

The reason the scenario posits an invasion from so far away is that that's about how much distance it takes for a small speed difference here to translate into a day long time difference there.

Re: A delightful quirk of relativity theory

#87

Post by time_to_smile » Tue, Jan 18, 2022, 3:16 PM UTC

philipov wrote: post #83

irthomasthomas wrote: post #21

This would be more fun in a blog post. Twitter is a fucking horrible format for a complex analysis of special relativity. That aside, my favourite quirk from relativity is this: "The more you move in space, the less you move in time." Like relativity in general, it sounds simple enough, but it's consequences are profoundly shocking. (That is, if you take the time to understand it, and don't leap to the conclusion tha…

There is no room for free will in physics, period . All processes are completely deterministic. Even quantum processes might appear to be probabilistic if you look at individual particles, but the statistics are nevertheless completely deterministic: if you look at enough particles, a predictable shape will emerge. The future is set in stone and not only is there no way to change it, but the concept of changing the f…

You can even leave out the 'physics' part there.

"Free will" is a very poorly defined concept that mostly falls out of problems with theodicy in early moral philosophy. Since the idea of "free will" plays a major role in Christian ethics this notion has permeated a huge amount of the Western intellectual tradition, but only makes sense in the framework of other archaic philosophical questions around theodicy like "if god is omnipotent, omniscient, and omnibenevolent why is there evil?" This question is only remotely interesting if you have a cultural reason to need to believe that these three things must be true (or if you're curious about the development of the Western intellectual tradition, in which case it's a very important question to understand).

Re: A delightful quirk of relativity theory

#88

Post by awb » Tue, Jan 18, 2022, 3:24 PM UTC

Jeff_Brown wrote: post #86

awb wrote: post #61

Earlier quoted context omitted.

> Take the case of two people on Earth, one stationary and one travelling past in a car. They each have a different reference frame, and a different set events which make up their present. Now imagine that there is an alien government in Andromeda debating a possible invasion of Earth. In the reference frame of the person on Earth who is moving, the debate is still going on. But, in the reference frame of the station…

The reason the scenario posits an invasion from so far away is that that's about how much distance it takes for a small speed difference here to translate into a day long time difference there.

You could imagine an event happening a day later from a traveling car, but that’s about it. Two people can’t actually observe an event a day later from the same reference point (Earth), and naturally the event occurs at a singular time at Andromeda’s reference point. Same with any point between Earth and Andromeda. So, if you can’t observe it at different times from the same reference point did it actually happen at different times?

From the Wikipedia page on the thought experiment, check out Criticisms:

https://en.m.wikipedia.org/wiki/Rietdijk%E2%80%93Putnam_argu...

> The interpretations of relativity used in the Rietdijk–Putnam argument and the Andromeda paradox are not universally accepted.

> Howard Stein[5] and Steven F. Savitt[6] note that in relativity the present is a local concept that cannot be extended to global hyperplanes.

> Furthermore, N. David Mermin[7] states: That no inherent meaning can be assigned to the simultaneity of distant events is the single most important lesson to be learned from relativity. — David Mermin, It’s About Time

Re: A delightful quirk of relativity theory

#89

Post by tzs » Tue, Jan 18, 2022, 3:29 PM UTC

irthomasthomas wrote: post #73

irthomasthomas wrote: post #21

This would be more fun in a blog post. Twitter is a fucking horrible format for a complex analysis of special relativity. That aside, my favourite quirk from relativity is this: "The more you move in space, the less you move in time." Like relativity in general, it sounds simple enough, but it's consequences are profoundly shocking. (That is, if you take the time to understand it, and don't leap to the conclusion tha…

If you think about this in the quantum-mechanical framework, it appears to contradict this free-will problem. In relativity, reality is a solid block, and future events are as immutable as past (no free-will). But in QM this statement would be expressing a level of certainty which violates the measurement problem and Heisenberg's Uncertainty principle. In Penrose's recent book he posits an interesting hypothesis on t…

There was a PBS Space Time episode about a year ago that covered what I think is the same recent Penrose idea that you have mentioned [1].

[1] https://www.youtube.com/watch?v=PC2JOQ7z5L0

Re: A delightful quirk of relativity theory

#90

Post by bena » Tue, Jan 18, 2022, 3:33 PM UTC

awb wrote: post #61

irthomasthomas wrote: post #21

This would be more fun in a blog post. Twitter is a fucking horrible format for a complex analysis of special relativity. That aside, my favourite quirk from relativity is this: "The more you move in space, the less you move in time." Like relativity in general, it sounds simple enough, but it's consequences are profoundly shocking. (That is, if you take the time to understand it, and don't leap to the conclusion tha…

> Take the case of two people on Earth, one stationary and one travelling past in a car. They each have a different reference frame, and a different set events which make up their present. Now imagine that there is an alien government in Andromeda debating a possible invasion of Earth. In the reference frame of the person on Earth who is moving, the debate is still going on. But, in the reference frame of the station…

> I’m pretty sure this is wrong (or misleading) on multiple levels:

> 1) An event in Andromeda occurs at single moment, it’s our observation of the event that is warped. So there aren’t two realities, one where they’re still debating and one where they aren’t. In both realities the debate has concluded, it’s just our observation of the event takes place at different reference times.

Yeah, they're making the mistake of assuming a minute is a minute.

It's closer to the difference in angular motion vs linear motion. If you are closer to the center, you move very little linearly. If you are closer to the outer edge, you move very little angularly.

Now you look at the linear distance as time passed for the object and the angular distance as the amount of "space-time" an object has gone. The amount of "space-time" is constant. It's a bit of a wonky model, but it's probably the simplest one that encapsulates the concept.

So just because they spent 3 days debating, you spent 5 days watching, and Bob only spent 1 day watching; that doesn't mean Bob is 2 days ahead of Andromeda and 4 days ahead of you. Since we are all also traveling through space at different speeds, we've all traveled the same amount of space-time, so we're all seeing the same things.

As for our perception, that more depends on our relative positions from each other rather than speed. Because nothing is faster than light, we can never experience an event before we see it.