Comment by javert | Hacker News Reader

Comment by javert | Hacker News Reader

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I'm fairly convinced this is intellectual masturbation. I think two situations are being confused for one another:

a) If you travel close to the speed of light, causality goes more slowly (e.g. a clock ticks more slowly) than it does for someone who is stationary. So, two clocks will diverge. This is true, AFAIK.

b) If you travel close to the speed of light, and somebody else is stationary, they are traveling "into the future" relative to you, whereas you are "in the past" relative to them. I believe this is nonsense. But, I believe this is required for the "Andromeda Paradox" to hold. Thus, I don't think it holds. (BTW, we know that paradoxes never hold, so there must be something wrong with it.)

The solution to the Andromeda Paradox that I am proposing is to say that there is one universal ordering of events (among both observers and the Andromedans), but the two Earthling observers have different times on their clocks at the particular point in the sequence of events where the Andromedans decide to invade.

>The solution to the Andromeda Paradox that I am proposing is to say that there is one universal ordering of events

Proposing this is fine, but proving it is quite a matter altogether - you have to replace special relativity. Special relativity pretty much explicitly states this isn't the case, making an exception for events that are causally connected, but there's been a slew of experiments over the past several decades that call into question even that exception at long distances, and more recently, even ones for local observers, e.g. https://advances.sciencemag.org/content/5/9/eaaw9832

Personally, I'm in the Rovelli and loop quantum gravity camp - time probably isn't actually a real thing on its own, and what we perceive as time is just an emergent property of thermodynamics.

To be clear, my conception of a "universal ordering" doesn't mean we can always measure when things happen relative to one another. If two things are causally related, we know one happened first. If a tree falls on Andromeda "right now," I don't know if that happened before or after a particular timestamp here on Earth, but it either did or it didn't. (Same goes for all possible timestamps for all clocks going at whatever speed they are going; their timestamps will diverge, but they could still be ordered if we knew the speed they travel relative to light and the starting value and how often they tick, e.g. once per second nanosecond or whatever. So if we had an observer on Andromeda with such a clock, we could eventually order events there relative to events on Earth based on the timestamp they report, though it would take a very long time for their report to reach Earth).

Are you sure that's not compatible with special relativity? Genuinely asking. If not, is it possible to explain why it isn't? I'd like to know (but if I'm asking you to write a book, never mind).

When you say you're in the Rovelli and loop quantum gravity camp - is that compatible with special relativity? I'm guessing yes, but let me know.

I think time is an emergent property of causality. That sounds close to what you are saying (possibly a different way to say the same thing).

I agree! Time is emergent. It is only comparing one thing moving relative to another thing. Without anything moving relative to each other, time can't exist:

https://youtu.be/A-2XQQDD6QQ

Yea, i think time is kind of used to define two different things and that seems to make these discussions confusing. I think if you are close to the speed of light, your atoms are moving slower than those of the stationary person and so your local clock time seems to stay constant while the stationary persons clock time seems to speed up in relation. But it's all a matter of perception of clock time passing and now is the same everywhere.

I believe what you’re talking about with an universal ordering of events is called the Relativity of Simultaneity. https://en.m.wikipedia.org/wiki/Relativity_of_simultaneity

I believe you are correct in that the closest you can get to change the order of two events is to make them simultaneous (in the case of photons, which do not experience time) but you cannot change one event ordering beyond that since that would violate causality.

You could change the event ordering by forcing some events to take a longer path through space?

For a real world example, we can predict supernovas because we've already seen them from another trajectory of light: https://youtu.be/ljoeOLuX6Z4 so we can both see the remote event before and after local events

Relative to a clock on earth, moving at a given speed relative to the speed of light, the supernova happened when it happened.

All that is changing with lensing is that you're seeing the light coming from it earlier looking in one direction than another. Either way, it happened in the past. The order of events is not changing.

It's like saying that a stock trader using a fiber connection figures out about a price movement more quickly than a stock trader using a dial-up connection.

At least, I think that's right; not a physicist.

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