1. Subscriberdivegeester
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    14 Oct '16 11:414 edits
    I am led to believe that the age, in years, of the universe is something in the region of 13.8 billion.

    I have an issue with this; how do we know for sure? Age is the passing of time from one point along its axis (for want of another adjective) to another, and is measured by us in billions of years. I.E. 13.8 billion. A year being approximately 365 earth days or one solar circuit of the the planet earth.

    Age is fine; we use years as a good measure, it makes sense to us from our tiny perspective. But what about time itself? Time is a "timy-whimy" thing which is not fixed, it is relative. As I understand it time is relative in different places depending such factors as mass and movement of mass through space.

    Now, the universe is expanding at almost the speed of light (is that correct?), or very fast, and it's expansion speeding up. So mass, the fabric of space and time is being stretched enormously over the "time" since the big bang. So time as we observe it now was probably passing very differently before the earth was formed and very different at different places within the expanding universe. Time travels slower for an object or mass relative to something else moving at a different rate.

    So, if time is variable and relative, how can we say with any certainty that the universe is X years old?

    Thanks.
  2. Cape Town
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    14 Oct '16 11:57
    You are generally correct that time is relative and time between us and say something very close to a black hole may be very different. But for most macro objects, the time discrepancies are actually not that great as they are not travelling at relativistic speeds. In summary, the vast majority of timelines in the universe aside from those near black holes are approximately the same length.

    Some points about expansion:
    1. It is space expanding, not objects moving away from each other, so technically the relative time effect doesn't happen as far as I know.
    2. The expansion can only be measured in percentages per unit time or in terms of a given value per unit distance per unit time. The actual total relative speeds of opposite sides of the universe depends on the size of the universe which is unknown and may be infinite. It is true that opposite sides of the observable universe are moving away from each other faster than light.
  3. Cape Town
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    14 Oct '16 11:59
    Also, we are talking about time since the big bang. It is unknown whether that was the start of the universe.
  4. Subscribersonhouse
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    14 Oct '16 12:29
    Originally posted by twhitehead
    Also, we are talking about time since the big bang. It is unknown whether that was the start of the universe.
    It could have been just our LOCAL big bang and it happens again and again if the big bounce theory is correct.
  5. Cape Town
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    14 Oct '16 14:25
    Originally posted by sonhouse
    It could have been just our LOCAL big bang and it happens again and again if the big bounce theory is correct.
    There are a number of possible scenarios, and no evidence in favour of any of them.
  6. Subscribersonhouse
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    14 Oct '16 15:41
    Originally posted by twhitehead
    There are a number of possible scenarios, and no evidence in favour of any of them.
    Yes, we can agree on that!
  7. Cape Town
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    14 Oct '16 15:48
    Another important point to note is that when we say 'the age of the universe is X' we mean the time since the big bang for us on planet earth. Since time is relative we cannot rightly say what the time on Alpha Centuri is, or what time it is in a galaxy a billion light years away. We can say how long the light took to get from there to here. But what time it is 'now' in that galaxy just doesn't make sense.
  8. Standard memberchaney3
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    14 Oct '16 20:42
    Originally posted by twhitehead
    Also, we are talking about time since the big bang. It is unknown whether that was the start of the universe.
    Your statement proves that much is unknown. It also leaves room for the possibility of a God, or of a Creator for those things unknown. Why atheists will not concede this option is curious.
  9. Standard memberDeepThought
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    14 Oct '16 21:111 edit
    Originally posted by twhitehead
    Another important point to note is that when we say 'the age of the universe is X' we mean the time since the big bang for us on planet earth. Since time is relative we cannot rightly say what the time on Alpha Centuri is, or what time it is in a galaxy a billion light years away. We can say how long the light took to get from there to here. But what time it is 'now' in that galaxy just doesn't make sense.
    Observers exist in frames of reference and have natural coordinate systems associated with them. For example the Schwartzschild solution has a set of coordinates appropriate to an asymptotic observer, that is one far away from the black hole and stationary with respect to the singularity. The coordinates appropriate to something falling in are called Gullstrand–Painlevé coordinates, which there's a page on Wikipedia about. We know how to transform between the two coordinate systems, so if we have two events and coordinates for them from the point of view of the asymptotic observer then we can work out the coordinates for them from the point of view of the infalling observer.

    With regard to this discussion, the time a given observer would have measured since the big bang is fairly well defined. Since Alpha Centauri is only 4 light years away and the big bang happened ~13 billion years ago they'll be getting the same headline figure. Suppose we were to send a signal to AC, the signal takes 4 years to get there and they send a reply which we get a further 4 years on. Suppose they timestamp the message so we know when they sent the message in their reference frame we can convert to our coordinates to work out the time they sent the signal in our reference frame and check their timestamp is correct based on when we received the signal. So I don't agree with your statement that time for other observers is unknowable to us. This is not the same as insisting on Newtonian simultaneity. Suppose we received a signal from Andromeda, we know it was sent two and a half million years ago and so we know how long since the big bang it was in Andromeda at the time the signal was sent and we can calculate how long a time has elapsed from the point of view of the sender in Andromeda (who told us their state of motion relative to the cosmic microwave background is) since they sent the message.
  10. Standard memberDeepThought
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    14 Oct '16 21:24
    Originally posted by divegeester
    I am led to believe that the age, in years, of the universe is something in the region of 13.8 billion.

    I have an issue with this; how do we know for sure? Age is the passing of time from one point along its axis (for want of another adjective) to another, and is measured by us in billions of years. I.E. 13.8 billion. A year being approximately 365 ...[text shortened]... ble and relative, how can we say with any certainty that the universe is X years old?

    Thanks.
    Assuming the theories are not too wildly out it's the correct answer. There is a concept in General Relativity called proper time. All observers agree on the proper time between two casually connected events. So all observers agree on the proper time that has elapsed since the Big Bang from the point of view of any particular observer. In other words they agree on what a particular observer at a particular time and place and in a specific state of motion would say.
  11. Cape Town
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    14 Oct '16 21:34
    Originally posted by chaney3
    Your statement proves that much is unknown.
    Correct. Very much is unknown.

    It also leaves room for the possibility of a God, or of a Creator for those things unknown.
    Correct. But not the Christian God.

    Why atheists will not concede this option is curious.
    Most atheists would readily concede it, myself included. But do not confuse 'room for possibility' with 'likely' or 'reasonable explanation'.
    I for one have never argued against the existence of God because of a lack of room for a creator in the range of possible explanations.
    That you do not realise this is curious.
  12. Cape Town
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    14 Oct '16 21:41
    Originally posted by DeepThought
    This is not the same as insisting on Newtonian simultaneity.
    Yes, I was more thinking of the absence of proper simultaneity, but even so, I probably got it wrong.
  13. Standard memberchaney3
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    14 Oct '16 21:42
    Originally posted by twhitehead
    Correct. Very much is unknown.

    [b]It also leaves room for the possibility of a God, or of a Creator for those things unknown.

    Correct. But not the Christian God.

    Why atheists will not concede this option is curious.
    Most atheists would readily concede it, myself included. But do not confuse 'room for possibility' with 'likely' or 'reas ...[text shortened]... m for a creator in the range of possible explanations.
    That you do not realise this is curious.[/b]
    Okay twitehead. With much respect and curiousity, leaving out the Christian God and the Bible God.....you would be open to 'something' such as a Creator?

    Sonhouse recently started a thread in spirituality forum stating the same concept, why he does not agree with the bible god.
  14. Subscribersonhouse
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    14 Oct '16 21:55
    Originally posted by chaney3
    Okay twitehead. With much respect and curiousity, leaving out the Christian God and the Bible God.....you would be open to 'something' such as a Creator?

    Sonhouse recently started a thread in spirituality forum stating the same concept, why he does not agree with the bible god.
    I don't agree with the bible god because it is a story told by men. If a god want's to talk to me, I might be all ears if I can conclude I am not hallucinating but I sure as hell can deny the bible god since it is the biggest scam humans have ever foisted on other humans and the truly sad part is how successful this scam has been.

    I can't deny a god may exist, we are too tiny in the universe to just blanket say there is no god or no gods.

    It is clear though, if there is some kind of god, it cares little for humans and we are on our own to live, die, succeed, fail, thrive or go extinct, it is on us and us alone.
  15. Standard memberchaney3
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    14 Oct '16 22:04
    Originally posted by sonhouse
    I don't agree with the bible god because it is a story told by men. If a god want's to talk to me, I might be all ears if I can conclude I am not hallucinating but I sure as hell can deny the bible god since it is the biggest scam humans have ever foisted on other humans and the truly sad part is how successful this scam has been.

    I can't deny a god may ...[text shortened]... d we are on our own to live, die, succeed, fail, thrive or go extinct, it is on us and us alone.
    What's most respectable about your position is that 'a God' might exist.

    It's only the Bible that claims this 'God' actually cares about us humans. If you remove that, and suppose a 'Creator' exists with no pre-disposed allegations, then a Creator becomes more welcomed.

    Meaning: we cannot have it both ways. God cannot tell us how much He loves us, when any news story will prove otherwise.
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