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derek yau
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if you were on a planet a 1000 light years away and had a really good telescope, would you be able to see a 1000 years into Earth's past? Is it as straight forward as this or what problems might this present?
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\ future / ^
\ / | time
\ / |
present \ / present |
(absolute \/ (also known as the +---------------------->
elsewhere) /\ absolute elsewhere) | space
/ \ |
/ \ |
/ \ |
/ past \ |
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I basically agree with what you're saying, but I don't think the "absolute elsewhere" is usually referred to as "the present", although it's true that for any two events with a spacelike separation, there is some reference frame where the two events happen at the same time-coordinate. But there are also plenty of reference frames where they don't, and the question seems to presuppose we're using a reference frame where the event of someone receiving the light from an event on Earth happened 1000 years after the actual event. Anyway, there would be a lightlike separation between the event on Earth and the event of a distant observer seeing it, not a spacelike separation.mitchellmckain said:Theoretically yes. But in relativity 1000 years ago on Earth could be considered as part of that planet's (1000 ly away) present. The following diagram might help explain.
The point is that if a place and time cannot be causally connected to the here and now then it cannot really be called the past, and might more properly be called the present. Afterall what part of this absolute elsewhere is simultaneous with your present time is relative, that is it depends entirely upon what inertial frame you are in.Code:[FONT=Courier New] \ future / ^ \ / | time \ / | present \ / present | (absolute \/ (also known as the +----------------------> elsewhere) /\ absolute elsewhere) | space / \ | / \ | / \ | / past \ | [/FONT]
The true past and future cannot be simultaneous with your present regardless of your inertial frame and it is causally connected to your present moment.
But the difference is crucial, because if there is a light-like separation, then all frames will agree on which event is in the past and which is in the future. And obviously for you to see an event at all, there must be a light-like separation between you and that event, and a moment later there is a timelike separation (you go inside that event's future light cone). So I don't think it makes sense to argue that you aren't seeing into the past when you see distant events--you are, in an absolute sense.mitchellmckain said:No it is not usually referred to as the present, therefore I gave my justification for using the term present. You could use the term absolute present as opposed to relative present if you like. A light-like separation is less than a second away from a space like separation.
JesseM said:But the difference is crucial, because if there is a light-like separation, then all frames will agree on which event is in the past and which is in the future. And obviously for you to see an event at all, there must be a light-like separation between you and that event, and a moment later there is a timelike separation (you go inside that event's future light cone). So I don't think it makes sense to argue that you aren't seeing into the past when you see distant events--you are, in an absolute sense.
To resolve something the size of a building at 1000 light years will need a telescope about the size of the Earth's orbit. I would think light gathering power wouldn't be so much of a worry.mitchellmckain said:Being able to see things with any detail at distances like 1000 light years requires long exposure photography in order to collect sufficient photons. To be able to see events on the surface of the Earth would take an awful long exposure, so that you would only be able to see the somewhat stable features of the Earth's surface like the geography and maybe a few buildings.
Currently, it is not possible to physically see into the past. However, scientists are able to study past events and make educated guesses about what may have happened based on evidence and data.
Scientists use a variety of methods to study the past, including analyzing fossils, examining geological layers, and studying historical records and artifacts.
While the concept of time travel is often associated with seeing into the past, it is not necessary. By using scientific methods and technology, scientists can gather information about the past without physically traveling through time.
The furthest we can currently see into the past is about 13.8 billion years, which is the estimated age of the universe. This is based on observations of cosmic microwave background radiation.
Yes, there are limitations to our ability to see into the past. For example, some events may not leave behind any evidence or data for scientists to study, making it impossible to accurately understand what happened. Additionally, the further back in time we try to see, the less reliable our information may be due to the degradation of evidence over time.