[Lord Dave]

Because if an alien from 2022 can travel to 1804, while I, who stay in 2022, exist, then there must be two copies of the universe.  One in 1804, one in 2022.  Or at least the information of its configuration must be such that it can be reconfigured once you are in 1804 to be that time.

Perhaps the problem is I don't understand "blocktime" because right now its sounding like every event exists all at once and you can do things like move from the future to the past and have all the matter and energy in the past configuration without affecting anyone in the now.  Which implies that either the universe has copies, or I reversed all the entropy in the universe to a specific point.

You and the alien would just be viewing the same “original” event from two different reference frames.  Before he travels, both of your reference frames are the same, now.  The alien changes his reference frame when he travels back.  Your frame is still your now, but his now becomes your past. 

The people on an airplane traveling towards a lightning strike will perceive it before someone stationary on the ground.  They don’t see an “original” strike and a “copy” strike.  They see the same strike from two different reference frames.

Your analogy of a movie was pretty close.  Changing reference frames or “teleporting” to the past or future would be the analog of  rewinding   or fast forwarding the movie.  There’s only one movie.  Nothing about it has to change or be copied to fast forward or rewind.  The only thing that changes is which part of it you are experiencing.

The difference is that I see a lightning strike's effects (photons) as they travel.  Their incremental changes in position.  So frame of reference is just where I am when the photons hit my eyes.

This is entirely different.  This is seeing photons that stopped traveling before you were born.  So either those photons have to always exist, or the universe needs to rewind with everything except you. 

To out it this way:
If I fire a photon at a wall, it hits it, is absorbed, and emits another photon.
How can I see that first photon after it was absorbed?  Its gone.  So it either exists in the past in such a way as to physically exist for me to interact with after its gone or I need to un-emit the photon.

[Knickknack]

If I fire a photon at a wall, it hits it, is absorbed, and emits another photon.
How can I see that first photon after it was absorbed?  Its gone.  So it either exists in the past in such a way as to physically exist for me to interact with after its gone or I need to un-emit the photon.

If you stay in the same reference frame, you can’t.  But theoretically, if you could change your reference frame, you could travel back to a time before the photon was absorbed. It doesn’t need to be un-emitted.

You are getting hung up on the time travel stuff, you are missing the bigger picture.

The difference is that I see a lightning strike's effects (photons) as they travel.  Their incremental changes in position.  So frame of reference is just where I am when the photons hit my eyes.

A lightning strike is an event and so is each incremental change in position of a photon.  An event either happens simultaneously in two different reference frames or it doesn’t.  Einstein used the example of two lighting strikes on either end of a moving train. From the platform, the strikes would appear simultaneous.  From the train, they wouldn’t.  Relativity says that if the frames are in relative motion, events won’t happen simultaneously. Time is literally experienced differently.  That makes makes presentism logically impossible.

If you think that means there must be an infinite number of copies of every moment in the universe, your problem is with relativity, not block time.

[Lord Dave]

I read up a bit.
Then flashed of college physics comes to mind and I remember how much I hated frame of reference in Relativity....

[Knickknack]

I read up a bit.
Then flashed of college physics comes to mind and I remember how much I hated frame of reference in Relativity....

It can definitely be hard to wrap your head around.

[Алёна]

So you met Parisfal irl?

She's actually also Parsifal, silly.

I suspect Pete is actually not an alt of Parsifal as Pete happens to beat her meat everyday.
Or maybe finger but I'm not sure.

[Rushy]

No it doesn’t.  Just because an event isn’t accessible to an observer doesn’t mean it doesn’t exist.

Actually that's exactly what it means. An event that you cannot observe does not exist. It's not real, it didn't happen. It's why relativity is fraught with meaningless thought experiments: because the real experiment requires the observer be in multiple reference frames simultaneously. The best you can ever do is have two different observers record their findings and assume that neither of them is lying. In other words, they existed in two different realities, then you must combine them into one reality and have them talk about two different realities that don't provably exist anymore.

That the past 'exists' is simply false. There's no mathematical way to verify it exists. You can't calculate the past based on the present and the present is all you ever have access to view. To think otherwise is to claim you can observe a water molecule and calculate its origin when that obviously isn't correct.

[Алёна]

The only thing that exists as of this moment is the present.
We are always in the present, even if we time travel it would seem like we're in the future but we're actually in the present still.
It just seems like the future as things have changed but we're just in today's present.