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Serifos
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... where was our current place in spacetime, call it A, when that photon started its journey 12 by ago?
Did A even exist 12 by ago?
Did A even exist 12 by ago?
Assuming you mean by by billion years, then the answer is simply yes. Where else should have the photon come into existence?Serifos said:... where was our current place in spacetime, call it A, when that photon started its journey 12 by ago?
Did A even exist 12 by ago?
I assume "by" is an abbreviation for "billion years"?Serifos said:... where was our current place in spacetime, call it A, when that photon started its journey 12 by ago?
Did A even exist 12 by ago?
rootone said:If you meant 12 billions of light years, the same is still true, we see then 12 billion years later.
fresh_42 said:Assuming you mean by by billion years, then the answer is simply yes. Where else should have the photon come into existence?
No. there were no people and no Earth simultaneous with when the photons were emitted.Serifos said:Did that "we" exist 12 by ago?
1. Labeling a specific location in space doesn't mean that location has physical existence in any meaningful sense. The abstract concept of "this location" varies depending upon your assumptions. In particular, it varies depending upon your reference frame. Imagine, for example, two cars going opposite directions on a highway and passing by one another. What is the "real" past location of that point where they pass? Is it the location of an observer standing beside the highway? Of one of the drivers? There's no absolute way to say whose perspective is the "right" one.Serifos said:So, the current place Earth occupies, existed 12 Billion Years ago? How about 13, or 14 BY ago? apparently, the universe did not exist more than 13.8 BY ago!
kimbyd said:...
The typical way we try to resolve this ambiguity in cosmology is by picking an observer for whom the universe looks simplest: an observer who is stationary with respect to the cosmic microwave background. But this is an arbitrary choice. Any valid slower-than-light trajectory can be used to define the past position of a point in space (these are known as timelike curves).
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Well, regions don't just begin to or cease to exist. I'll try to explain how General Relativity describes the universe, and hopefully that will help you to see how this works (I have a hard time just directly answering your question because, well, General Relativity is weird and doesn't necessarily describe the universe the way you'd think).Serifos said:Thank you very much for your comments. I'm trying to understand them and hopefully I'll get there :-)
For an alternate phrasing of my original question, and to clarify it for a couple more posters that had questions, here's an analogy that hopefully can be a bit clearer about what I'm trying to ask:
In our current everyday and common time scale, if start from some point A in space and travel at human-scale velocity V towards some direction in space (disregard planets, stars or other objects), after some human-scale time T I will arrive at some point B. That point B was there already when I started my travel from point A. Correct?
Serifos said:where was our current place in spacetime, call it A, when that photon started its journey 12 by ago?
Serifos said:Did A even exist 12 by ago?
Serifos said:if I leave now from where I am, and travel at the speed of light for 12 billion years towards some empty spot in the sky (assuming I won't hit any planet, star, etc), is the destination I will arrive to, there already?
PeterDonis said:...
I think you mean our current place in space.
A photon is a fundamental particle of light that carries electromagnetic energy. It is the smallest unit of light and has no mass or charge.
A photon is able to travel through space at the speed of light, which is approximately 186,000 miles per second. This allows it to cover vast distances in a relatively short amount of time.
Scientists are able to measure the distance of galaxies based on their redshift, which is a result of the expansion of the universe. By using this method, we can determine the distance and time it took for the photon to reach us.
Due to the immense distance that the photon had to travel, it took 12 billion years for it to reach Earth. This is because light moves at a finite speed, and the distance between galaxies is vast.
By studying the properties of the photon, such as its wavelength and energy, we can learn about the conditions and processes that existed in the universe 12 billion years ago. This can provide valuable insights into the early stages of the universe and its evolution over time.