What Does Einstein's Space-Time Theory Reveal About Observing the Universe?

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Discussion Overview

The discussion revolves around the implications of Einstein's space-time theory for observing the universe, particularly in relation to the concepts of distance and time. Participants explore how observations of distant objects relate to their current positions and the nature of time in the context of relativity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question why Einstein combined time and space, suggesting it complicates the understanding of where and when an object is observed.
  • Others argue that for most practical purposes, such as measuring distances to galaxies, simpler physics can suffice without invoking space-time concepts.
  • There is a discussion on how observations of distant galaxies reflect their past positions, leading to uncertainty about their current locations.
  • One participant mentions various methods for determining distances to galaxies, suggesting that while space-time may not be necessary, understanding relative time is complex due to the lack of absolute time in relativity.
  • Another participant emphasizes that while galaxies move, their new positions can be calculated using mathematical methods, indicating a reliance on observational data and models.
  • One post elaborates on the implications of observing light from distant objects, relating it to concepts of time travel and the potential for paradoxes in different reference frames.

Areas of Agreement / Disagreement

Participants express a mix of views, with some agreeing on the utility of simpler physics for certain observations, while others emphasize the importance of space-time in understanding the universe. The discussion remains unresolved regarding the necessity and implications of combining time and space in observations.

Contextual Notes

Participants highlight limitations in understanding due to the complexities of relativity, including the dependence on reference frames and the challenges in quantifying "when" events occur in relation to observations.

binbots
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Why did Einstein combine time and space? Does this mean when we observe something we don't know where it is as opposed to when it is? Is a object 1 light year away or 1 light year ago. How do we separate the 2 to know where something actually is?
 
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You don't really need to bother with 4D until you start examining nasty things like black holes and the like, that is what spacetime is useful for. When talking about the examples you gave it is best to just stick with the simple physics - the object is 1 light year away, but we see what it looked like 1 year ago. The point in physics is to simplify reality, don't use concepts where they are not needed. Newtonian physics explains most stuff just fine, exotic theories like spacetime are there to accommodate for the bits which don't quite fit properly, and they are few and far between on our scale, when you get very small everything is messed up.
 
Is space time useful when talking about distances between galaxies. When we see 2 galaxies how do we know how far apart are they as opposed to when they are. If what we observe takes place in a past time, that means we haev no idea where a object it now. So when we look at a distant galaxy we don't know where it is now, when it was, or where it use to be?
 
I am in the beginning stages of relativity and space-time, but for distances between galaxies we determine this and cross check this with a few different measurement, i.e. Type 1a SN, Cepheids, Tully-Fisher, etc. so "space-time" isn't really needed. As for the question to "when" they are I don't think is quantifiable because when dealing in SR & GR there is no absolute time, it is relative to the observers refrence frame. It is true that when we observe say Andromeda, it's photons are from 2.5 MLY ago and since then it's location has indeed changed, but this does not mean we cannot know "where" it is in the present time. What we can do is we can infer it's "new" location first by determing its velocity via doppler shifts in its spectrum, and then combining that with time to solve for the distance. There are a few other aspects to it such as the radial & tangential components of the galaxy in question. Some one correct me if I am wrong. I hope I haven't sent the OP in the wrong direction.

Joe
 
Agent is totally correct, although the galaxy will have moved, we can work out its new position using simple maths.
 
binbots said:
Why did Einstein combine time and space? Does this mean when we observe something we don't know where it is as opposed to when it is? Is a object 1 light year away or 1 light year ago. How do we separate the 2 to know where something actually is?

The light which reaches Earth from an object 1 ly (light year) distant is 1 year old light, and is like looking at a delayed movie. Thus, when we observe a 13.7 billion ly distant object, we are seeing it as it was that many years ago because local c is invariant. It is in fact, this very concept of the absolute speed of light that leads to a combination of time and space.

If you traveled FTL (Faster Than Light) 1 ly distant, you would have traveled in time from your perspective. Only if you traveled Classically (Slower than light in this case) would you avoid this. After all, if you see a supernova 500 ly from earth, and instantly teleported (magically) to that star, it would be as it was 500 years from your observation of its 'death'. In fact, there is the time travel and the paradox. What if there were an inhabited world around this star, and you warned inhabitants to prepare for the end of their world? You would have changed history from the perspective of different observers!

This is why you will often hear that one of the fundamental principles of relativity is that observers in all intertial frames (people anywhere at any time) will agree on the ordering of events. A causes B, (cups shatter, they don't repair themselves as far as we can all agree), and if at any time distant observes can observe B causing A, there is the potential for paradox and closed time-like curves.
 

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