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Some Observers Perceive the Universe To Be Much Younger Than We Do 139

Posted by timothy from the your-parents-for-instance dept.
StartsWithABang writes: It's been 13.8 billion years since the Big Bang for us, and when we look out at a distant object in the Universe, we're seeing it as it was in the past. Its age — as it appears — is determined only by how long the light took for it to travel from that object to our eyes, but to someone living there, it will also appear that the Universe is 13.8 billion years old. But it is actually possible for an observer living on another planet, star or galaxy to perceive that significantly less time has passed since the Big Bang, so long as they were moving close to the speed of light relative to the CMB. Paradoxically, if they slowed their speed, they'd find that they themselves were very young, but living in a 13.8 billion year-old Universe.
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Some Observers Perceive the Universe To Be Much Younger Than We Do More

Some Observers Perceive the Universe To Be Much Younger Than We Do

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  • Weasel Words (Score:4, Funny)

    by Zanadou ( 1043400 ) on Sunday August 23, 2015 @02:46AM (#50372897)
    Some Observers Perceive the Universe To Be Much Younger Than We [Who?] Do

  • Lots of experts, infact (Score:3, Funny)

    by Anonymous Coward on Sunday August 23, 2015 @02:46AM (#50372901)

    Jeb Bush believes the universe to be somewhere between 4 and 5000 years old, so there's alot of diverse and nuanced opinion on this subject.

    • The Bushes have so many advantages, it doesn't seem fair that God also speaks to them personally.

      • Re: (Score:1)

        by Anonymous Coward

        To those that have shall be given. From those that have not shall be taken even that which they have.

      • The Bushes have so many advantages, it doesn't seem fair that God also speaks to them personally.

        A lot of the Republican candidates in the last presidential election claim God personally chose them to be president. Nasty to be fucking with the faithful like that.

      • I plead daily with God to not speak to me directly, again. This common amongst those who have had the experience. Life was simpler in the days I could think I wasn't really sure.

    • Jeb Bush believes the universe to be somewhere between 4 and 5000 years old?

      Hmm, I think even Jeb would have to concede that the universe is more than 4 years old.

    • Re:Lots of experts, infact (Score:4, Informative)

      by ShanghaiBill ( 739463 ) on Sunday August 23, 2015 @11:02AM (#50373937)

      Jeb Bush believes the universe to be somewhere between 4 and 5000 years old

      Jeb Bush is a Roman Catholic, and is not a Young Earther. There are plenty of legitimate reasons to criticize him, so stop making stuff up.

      • He makes stuff up. We make stuff up.

      • So you are saying that Roman Catholics don't believe the Bible?

        • Where in the Bible does it state that the Universe is six thousand years old? It is possible to twist the words to come up with a conclusion something like that, but when somebody starts interpreting it somebody else can come up with another interpretation.

          • Where in the Bible does it state that the Universe is six thousand years old?

            The methodology that Archbishop Ussher adopted was to tally up the ages of the various patriarchs listed in the Old Testament, then tie them to the historical record at about the Babylonian captivity and more recent events.

            They may have been working from ridiculous premises, with ludicrously limited data sources, but they were actually perfectly serious scholars.

  • New time reference (Score:1)

    by Anonymous Coward

    Instead of using some mythical person to determine that we live in "2015" after his birth, let's use the big bang as a time reference.

    Think of all the advantages!
    "I'll see you next monday at 8 o'clock *cough* +- 0.059 billion years"

    • Re: (Score:2)

      by Tablizer ( 95088 )

      Instead of using some mythical person to determine that we live in "2015" after his birth, let's use the big bang as a time reference.

      Then we'd have bloated dates like 12/25/13827642763

      Thank You Jesus!

      • Re: (Score:1)

        by Anonymous Coward

        Then we'd have bloated dates like 12/25/13827642763

        Thank You Jesus!

        I hope you mean 13827642763/12/25?

  • Someone has just discovered relativity and feels pleased as punch.

    • ...but only Special Relativity (Score:5, Interesting)

      by Roger W Moore ( 538166 ) on Sunday August 23, 2015 @11:32AM (#50374057) Journal
      Unfortunately I'm not at all sure that he actually got it right though because I think he has forgotten about General Relativity. He treats the entire universe as if it were a single object at rest in the CMB frame. However it isn't: it consists of many constituent components all with their own individual rest frames.

      As we look further away from us galaxies are travelling closer and closer to the speed of light and so appear "slowed down" by time dilation due to the expansion of space itself which you need general relativity to account for. All that travelling close to the speed of light should do is shift which galaxies are slowed by time dilation and which are in almost the same frame and so not slowed. Hence you would see effectively exactly what we see now but it will be different galaxies which are in view because you are in a different inertial frame.

      Hence I am not at all sure that he got it right. Certainly I'd like to hear it from a cosmologist before I believe it since GR is far more complex than SR and it is easy to get stung applying SR to a situation which requires GR and hence my cautiousness about whether he is wrong since I'm not a cosmologist. This would far from the first thing that he has got wrong...but it would be the first truly spectacular failure.

  • Inaccurate Summary (Score:5, Informative)

    by The Raven ( 30575 ) on Sunday August 23, 2015 @03:14AM (#50372935) Homepage

    A better way to put it is that when you are travelling nearly the speed of light, if you look behind you at the place you are heading away from time seems to stand still for it; the light from your old hometown is redshifted. But light that's coming in from in front of you (and thus, the perceived rate of time) is way higher. Time seems to be moving a hundred times faster than normal as you look at an oncoming blueshifted star. Then, the star passes you and all of a sudden it slows down... from your point of view.

    So from the point of view of the fast moving observer, time is sped up in front of them, and nearly frozen behind. As they travel they pass galaxies that are growing old very fast, but leave behind them a frozen universe, that is changing imperceptibly slowly.

    When they stop... they are not 'surprised' that the universe is old. They watched it grow old in front of them. Nor are they surprised that their home, now billions of light years away, has not changed much (it looks 'young') because behind them time seemed to stop. The perceived universe makes sense from the viewpoint of the traveler. Point being that there is no paradox. What happens to the fast moving universe would look really weird from inside (because of the starbow effect [sciencephoto.com]), but they would be used to it. You know... assuming they survived the X-Ray energy sleeting through them from impact with intergalactic matter.

    • How about any civilization in a galaxy at the edge of the universe. Is that even possible? What would they see on one side? Darkness and light on the other as they looked out into their neck of the cosmos?

      • The universe probably does not have an edge [askamathematician.com], though there is no way to know for sure because the vast majority of the universe is beyond our reach, expanding away from us faster than we could get there at the speed of light.

    • Huh?

      From your point of view, time will appear to happen slower on things moving fast relative to you, whether they're in front or in back. We've known about that since Einstein explained the Lorenz transform.

      • Why this works requires some use of the time dilation equation. Let's work with a relatively basic speed: 0.8c. That's the speed where time appears to be about 60% as fast (in both frames) when two ships are being compared to each other. Now let us imagine a ship flying away from the earth to a nearby star and back. In fact, let's steal the example given in this explanation of the Twin Paradox on Wikipedia [wikipedia.org]. You should go read that first, because I'm not going to repeat what it says here.

        There are two parts

        • That's not how it works.

          As the ship leaves Earth, it's in an inertial reference frame that show Earth aging slowly. As the ship approaches Earth, the same happens. The significant part happens in the deceleration and acceleration (all felt as acceleration aboard the ship). That makes the inertial reference frame change rapidly, and that's when the ship perceives most of the Earth time passing. (If the course change happens gravitationally, and hence without significant observable acceleration, we nee

          • I'm sorry, but you are incorrect.

            Perhaps you would like to explain how 8 years of communications reach the ship as it is 'changing frames' on the star 4 light years away? What you are describing requires information to travel at faster than light speeds. Can you explain when the doppler effect stops working as things get faster? Does the doppler effect stop working at 0.01c? At 0.1c? At 0.5c? Can you provide a source?

            Here is what happened to you, perhaps years ago. You read and partly understood the frequen

            • A more complete explanation (I should have checked earlier) can be found on Wikipedia: Relativistic Doppler effect [wikipedia.org]

            • Saying I'm wrong doesn't do much (and is wrong anyway). The ship doesn't receive years of communications suddenly, but the acceleration changes the ship's idea of when they were sent. You appear to be confused on time dilation. It isn't the doppler effect, and it isn't a matter of measuring signals as they arrive.

              The ship gets blue-shifted communication. The ship can measure how fast it's approaching the planet, and make allowances for that. It can measure where, from its point of view, radio waves

              • I explained, backed with math and citations, the relativistic effects on communication between the Earth and a ship; the entire timeline of the journey as perceived by both sides.

                The math for the Doppler effect combined with time dilation was demonstrated two ways, both by examining the time experienced by both sides (and working out the speed of the communication that would match that time) as well as examining the actual doppler effect separated out from the time dilation. The math, in both situations, wo

                • To put this very simply: you're using Newtonian physics in that analysis. When you use Newtonian physics when talking about relativistic velocities, you're going to get wrong answers sometimes.

                  When the ship observer receives the planetside pings has nothing to do with relativistic time dilation. It's an effect that can be explained by Newtonian physics, and therefore irrelevant for time dilation. What happens is that, when the ship observer notes down the times the pings arrive, and measures the dist

                  • So please describe what the ship observes on the entire trip. Not one moment. Do the math. Cite a source. Prove your point, rather than assert it.

                    I did.

  • Welcome to 1905... (Score:1)

    by Anonymous Coward

    when Einstein published the theory of special relativity. /. is a bit behind the times.

  • Yes, but. (Score:3, Interesting)

    by Doghouse13 ( 2909489 ) on Sunday August 23, 2015 @04:08AM (#50372995)
    Presuming they were able to detect the CMB - which would NOT look the same in all directions - and "correctly" identify it (i.e., presuming that that's what we've done), they would then also be able to calculate their own relative movement, and correct for it. So they'd reach pretty much the same answer that we do.

  • Paradoxically, if they slowed their speed, they'd find that they themselves were very young, but living in a 13.8 billion year-old Universe.

    I'm very young (compared to the universe), but I don't see a paradox when comparing myself to the universe's age.

    Okay, that's just me playing with words. But there's no paradox anyway.

    Paradoxically, if they slowed their speed...

    ...then they'd presumably be advanced enough to understand special relativity and take account for it in all their calculations.

    The twin paradox has been around - and understood - for over a hundred years. What's next on Slashdot? A Starts-With-A-Bang article on how we only ever see one side of the moon?

    And what would they be

    • Paradoxically, if they slowed their speed...

      ...then they'd presumably be advanced enough to understand special relativity and take account for it in all their calculations.

      Would they? A photon's momentum is a function of its frequency, thus an object in motion relative to the CMB - one who sees one half of the sky blueshifted and the other redshifted - is going to effectively experience friction and come to an asymptotic halt eventually.

      Of course, that is going to take a very long time. And that rises a q

      • Re: (Score:3, Interesting)

        by PaulMattSutter ( 3905379 )
        Yes, we do have motion relative to the CMB, and this causes one side of the CMB sky to appear hotter than the other. Here's an APOD [nasa.gov] describing it. So everything discussed in the article already happens to us, here on Earth, but in a much less significant way.

      • We don't have an effective velocity relative to the CMB. So therefore, your question, in and of itself, exposes some sort of flaw in our current understanding of the Big Bang.

        I'm just not sure what it is.

  • Haven't seen one on here for a while - was the guy on vacation?

  • Let's try to keep them all in once place.

  • Could a different observer identify the universe as being much older than us, by the same argument?

    Also, less seriously, if the rest of the universe is travelling away from us at light speed, but there's nobody on those planets to observe it, is it actually older?

  • the universe is not all the same age. near black holes are younger because of gravitational time dilation [wikipedia.org]. and even this depends on the frame of reference.

  • Ethan doesn't understand relativistic time (Score:3)

    by jurgen ( 14843 ) on Sunday August 23, 2015 @08:40AM (#50373347)

    He starts out with the Yuval Ne’eman quote about how less people understand relativistic time than believe in horoscopes. Correct, it seems a lot less because as he goes on to demonstrate even someone as enlightened as he himself doesn't understand relativistic time!

    Others have pointed out that talking about a galaxy moving a near light speed is purely hypothetical and not particularly interesting or different from other time-bending phenomena such as black holes. But the thing that makes this all completely meaningless (and shows that he doesn't really understand it) is that relativity tells us that there is no universal "now". It's pointless to talk about how old someone at another point in space (whether 100 lightyears or 13 billion light years from us) sees the Universe as being because you're only specifying 3 of his (at least) 4 space time coordinates, assuming the forth one to be "right now", but there is no "now". The "now" is just a convenience we use when the difference is so small as not to matter to us, but when any of the dimensions gets larger you have to specify all of them to say anything meaningful. You could specify the time dimension as a specific amount of time "passed since the big bang" (instead of "now"), but then the title of Ethans little essay becomes its own answer, demonstrating the meaninglessness of the whole exercise (i.e. "is everything that exists 13.8 billion years after the big bang the same age"?)

    • Re: (Score:2)

      by jurgen ( 14843 )

      To make sure that last sentence isn't misunderstood, make it "You could specify the time dimension as a specific amount of time passed since the big bang at that point in space... it always has to be all 4 coordinates!

    • We know the universe is expanding in space, I contend it is also expanding in time, and 'now' is the leading edge of the expansion of the universe in the time dimension.

    • Thought the same when I read "we don't see those galaxies as they are *today*." Today where? I think people fall in that trap by drawing a sketch of the entire universe on a sheet of paper, and as that sheet fits in their field of view entirely, they forget there is no universal now.

  • Sounds to me like an attempt to couch the entire argument in terms of a universal preferred frame of reference, which is the foundation for many, many fallacious arguments relating to relativity.

    • There is a dipole anisotropy observed in the CMB as observed from our local observations, which can be attributed to our local motion in reference to the CMB. I'll quote/steal the paragraph from Wikipedia (https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy),
      "From the CMB data it is seen that our local group of galaxies (the galactic cluster that includes the Solar System's Milky Way Galaxy) appears to be moving at 627±22 km/s relative to the reference frame of the CMB (al

  • "It's been 13.8 billion years since the Big Bang for us..."

    The guide in the science museum showed a graphic representation of the big bang to a bunch of kids with their teacher when one of them asked him how long ago that happened.
    The guide replied: Well that was 13,800,000,017 years ago.
    The teacher was astonished and asked the guide how he could be so sure about that very exact number.
    The guide replied: When I began working here, they told me it happened 13.8 billion years ago and I began working here 17 y

  • and we are in it. We know that gravity slows time, and we know that the distribution of matter in the universe is into filaments and the surfaces of 'bubbles'. In those places, like where we live, gravity slows time down unlike 'in' the bubbles and other voids between the filaments. So how much slower are we perceiving time with respect to 'universal' time?

  • ... moving close to the speed of light relative to the CMB...

    What does this mean? Isn't the CMB a kind of standing wave that fills the universe? a bunch of photons going off in all directions?

    Here is my take. I am not a cosmologist or astrophysicist. I know about as much math as the fetal Einstein.

    The universe began in a singularity with maximum separation distance of zero, and no meaningful earlier time. Next thing we know it is a dense space full of energy with the maximum separation (or the measureme

    • Isn't the CMB a kind of standing wave that fills the universe? a bunch of photons going off in all directions?

      Oops. I was winging it a bit since I had forgotten the definition/meaning of 'standing wave'. Here, let me have another shot on the range of bad analogies:

      The CMB is a bunch of photons that are everywhere and going nowhere else at the speed of light. Poor CMB photons, all sped up and no place to go.

      I almost got carried away and added 'on a computer'. Who knows, it might be patentable that way.
      --

  • An observer moving faster, but compared to what point?
  • It's like the Truman show. The UN flag is the actual map. There's a top, as well as sides. That's why we can't go to Antarctica: https://en.wikipedia.org/wiki/... [wikipedia.org]

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