Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: petelamana on 08/02/2018 21:25:17

Title: Is there a difference between spacetime and placetime?
Post by: petelamana on 08/02/2018 21:25:17

Is there a difference between spacetime and "placetime"?

Consider the following dark-matter map of the universe.  "It shows the distribution of dark matter in the relatively recent universe. The red patches are spots where the dark matter density is high, the blue parts are areas where its density is low."  Chihway Chang/University of Chicago/DES collaboration.

(https://images.theconversation.com/files/180975/original/file-20170804-17911-1qz2dh9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip)

Since we know that dark matter affects spacetime, this map seems to imply that there is a difference between spacetime and placetime.  Is there?

Title: Re: Is there a difference between spacetime and placetime?
Post by: Bored chemist on 08/02/2018 22:04:54

Define "placetime"

Title: Re: Is there a difference between spacetime and placetime?
Post by: petelamana on 08/02/2018 22:18:47

My original question sprang from a conversation I recently had with a friend.  I must admit to only being able to define placetime conceptually.  For that I am sorry.  Let me rephrase...

Can an object remain stationary in spacetime?  Is there such a thing as an absolute position in spacetime?

and

If it were possible to remain stationary, would you "see" time passing, and be unaffected by its passage?

Title: Re: Is there a difference between spacetime and placetime?
Post by: Ophiolite on 09/02/2018 06:10:15

Quote from: petelamana on 08/02/2018 22:18:47

My original question sprang from a conversation I recently had with a friend.  I must admit to only being able to define placetime conceptually.  For that I am sorry.  Let me rephrase...

Can an object remain stationary in spacetime?  Is there such a thing as an absolute position in spacetime?

and

If it were possible to remain stationary, would you "see" time passing, and be unaffected by its passage?

There is no absolute position in spacetime, hence it is only possible to remain stationary relative to another object. That being the case your second question has no meaning.

Title: Re: Is there a difference between spacetime and placetime?
Post by: opportunity on 09/02/2018 10:44:26

Ophiolite is right in the context of "absolute" being a "central place of space and time effecting all else" and how improbable that is given the effect of each reference on other references and vice-versa.

If we are though trying to entertain a discussion of "place-time" relevant to "space-time", it could only be a "unique" 0-reference of space "anywhere" as an independent entity from which a 3-d mathematical understanding and 1-d time appreciation can be discussed. It seems the initial question is relevant to how far out in space and time that works, on event horizons, and so on.

I have to share something here: being schooled in the 80's with science, secondary school, back then the big bang was taught to be the size of a basketball, and that when the event happened, the big bang, in our understanding of space, it "happened everywhere at once". I'm not sure how that washes today, but what I took from that schooling was that even space wasn't conceived pre-bang, and that when the event happened an infinite number of spatial references enjoyed the rapid expansion. Clearly that made me want to question science. I mean, I can understand using the reference of a basketball to inspire the basketball players in the room, but the question still remained, "why a basket ball", and now, "why the Planck scale"?

According to the Planck scale, the energy there is immense, and one could wonder when the next explosion is due. I know that sounds ridiculous, yet its certainly a task to know an alternative.