YB
BannerBanner

Physics question - light years and actual time

Page: 12 > Showing page 1 of 2
Author
paulthebuilder
Pro-Member
  • Total Posts : 27813
  • Reward points: 9300
  • Joined: 2006/05/06 22:39:09
  • Status: offline
2011/04/08 19:44:30 (permalink)
0

Physics question - light years and actual time

Scientists are currently observing a massive burst of gamma radiation in a galaxy 3.8 billion light years away.
I know the natural inclination would be to think that it therefore happened 3.8 billion years ago but I don't think this is correct.
Any heads up on the mathematics behind calculating the time elapsed relative to the distance?
Thanks.
#1

22 Replies Related Threads

    Griff87
    Senior Member
    • Total Posts : 132
    • Reward points: 3533
    • Joined: 2008/04/16 13:23:46
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/08 20:00:13 (permalink)
    0
    The speed of light or other forms of em like Gamma rays is a constant value. The measurement is the amount of red shift or blue shift of the wave. Edit- the red shift is when the wavelength has increased and frequency decreased and the opposite for blue shift. The effect is caused by the fact the universe is expanding. A wave heavily redshifted has travelled for a long time at a set speed. Speed and time can be used to calculate distance. I hope I haven't got anything wrong in all that. I'm sure some one can correct me if I have.
    post edited by Griff87 - 2011/04/08 20:07:03

    The pain may come over you, but don't let it overcome you.
    #2
    Ricky116
    Senior Member
    • Total Posts : 139
    • Reward points: 5242
    • Joined: 2006/08/19 04:00:29
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/08 20:52:03 (permalink)
    0
    I'm not sure what you are asking really but obtain recessional velocity using redshift then obtain distance using Hubble's Law. Calculate time it takes for light to travel that distance and that's how 'long ago' it was.
     
    Why don't you think the natural inclination of time = distance/speed is correct?
     
     
     
    #3
    keyser soez 2010
    Pro-Member
    • Total Posts : 3238
    • Reward points: 3012
    • Joined: 2010/02/19 17:51:45
    • Location: The emerald isle
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/08 20:57:15 (permalink)
    0
    Ill be back soon with the answer , i know i know this but it has just slipped my mind at the moment.

    #4
    paulthebuilder
    Pro-Member
    • Total Posts : 27813
    • Reward points: 9300
    • Joined: 2006/05/06 22:39:09
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/08 21:21:45 (permalink)
    0
    Ricky116
    Why don't you think the natural inclination of time = distance/speed is correct?

    Time dilation and the work of Lorentz, of which I have only very brief knowledge, among several factors relative to the magnitude of "space".
    I remain unknowing rather than skeptical.
    #5
    Dick Dastardly
    Pro-Member
    • Total Posts : 5674
    • Reward points: 9388
    • Joined: 2006/08/17 11:41:32
    • Location: Dubai
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/08 21:23:28 (permalink)
    0
    42
     
     
     
     
     
     
     
     
    post edited by Dick Dastardly - 2011/04/08 21:26:16

     PB's 1RM

    Deadlift 270kg      
    Bench   140kgx2 New PB as of Nov 16 woo!
    Squat    210kg  
    #6
    dazc
    Pro-Member
    • Total Posts : 29654
    • Reward points: 11750
    • Joined: 2003/04/02 08:23:02
    • Location: United Kingdom
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/08 21:24:20 (permalink)
    0
    way above my physiscs grade! lol
    #7
    Ricky116
    Senior Member
    • Total Posts : 139
    • Reward points: 5242
    • Joined: 2006/08/19 04:00:29
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/08 22:15:07 (permalink)
    0
    Time dilation only 'matters' to the relatively moving bodies, in this case light and us.
     
    From the photons frame of reference, it experiences zero time and zero distance because it is travelling at c relative to the universe. If you were a photon, you would set off from point A at time = t, travel zero distance and appear at point B at time = t.
     
    We observe the photon with zero length, but not the universe (as in, the gap between us and the photon) as we are moving relative to the photon at light speed, not the universe. Therefore the universe is only negligibly length contracted by our velocity and our measurements are correct.
     
    So very very confusing. I'm not 100% on this at all.
    post edited by Ricky116 - 2011/04/08 22:16:44
    #8
    James
    Moderator
    • Total Posts : 50969
    • Reward points: 14826
    • Joined: 2000/11/10 18:09:18
    • Location: Northants, UK
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 13:48:59 (permalink)
    0
    and for us non-physics geeks, what's the answer?
    #9
    theITman
    Pro-Member
    • Total Posts : 4841
    • Reward points: 2228
    • Joined: 2009/12/22 22:25:44
    • Location: Trapped in a box!
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 13:51:02 (permalink)
    0
    I think, that basically we moving in an expanding universe, as is source of the burst, thus keeping everything  constant and the time the scientists claim to be correct?
    #10
    tac
    Pro-Member
    • Total Posts : 9600
    • Reward points: 8097
    • Joined: 2005/05/13 17:34:06
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 14:19:39 (permalink)
    0
    theITman

    I think, that basically we moving in an expanding universe, as is source of the burst, thus keeping everything  constant and the time the scientists claim to be correct?

    ^^^ that, in simple terms.
     
    distance = time = distance.
     
    lorentz effect doesnt apply as light speed is a constant (ie it can only effect the frequency not the velocity at light speed, as the speed of light cannot vary in either absolute OR relative terms ).
    post edited by tac - 2011/04/09 14:21:18


    #11
    Will8801
    Pro-Member
    • Total Posts : 2910
    • Reward points: 7220
    • Joined: 2006/08/04 20:25:53
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 14:37:46 (permalink)
    -1 (1)
    rightyho

    Scientists are currently observing a massive burst of gamma radiation in a galaxy 3.8 billion light years away.
    I know the natural inclination would be to think that it therefore happened 3.8 billion years ago but I don't think this is correct.
    Any heads up on the mathematics behind calculating the time elapsed relative to the distance?
    Thanks.

     
    First of all welcome to MT 
     
    Mate just keep it simple, I think your over complicating things.
     
    Post up your diet up first and read the beginner articles.
     
    Just dont forget if you want to get big eat big and forget all this Gamma radiation/light years nonsense for now

    """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
    #12
    tac
    Pro-Member
    • Total Posts : 9600
    • Reward points: 8097
    • Joined: 2005/05/13 17:34:06
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 15:06:25 (permalink)
    0
    ^^^ fpmsl 


    #13
    Wayne Cowdrey
    Olympian Member
    • Total Posts : 965
    • Reward points: 7981
    • Joined: 2007/08/08 12:57:08
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 15:15:09 (permalink)
    0
    The obvious answer is that it happened 3.8 billion years ago. Is it as simple as that? I don't know. The distance from us to there will have changed (increased with expansion?) massively over time. If it's 3.8 billion light years away now, it doesn't mean it was the same distance away 3.8 billion years ago. I'm confused!
     
    3.8 billion light years.... what an inconceivable distance!!!!
    #14
    Entrophy
    Pro-Member
    • Total Posts : 1014
    • Reward points: 8931
    • Joined: 2006/06/16 10:42:27
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 15:15:10 (permalink)
    0
    there is no spoon only the matrix
    #15
    Liddy
    Pro-Member
    • Total Posts : 1933
    • Reward points: 4759
    • Joined: 2010/01/10 13:44:11
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 15:16:43 (permalink)
    0
    Light years is a measurement of Distance rather than time (which some people misunderstand)
    Simply the distance light travels in a year.

    Light travels at 299 792 458 m / s

    Only thing that I know travels faster than the speed of light is subatomic tachyons.
    Gamma is part of the electromagnetic spectrum, therefore travels at the quoted speed of 299 792 458 m / s

    So yea, if it's 3.8 billion light years away, it happened 3.8 billion years ago. 
     
    But...... I'm often wrong around here lol.
    post edited by Liddy - 2011/04/09 15:18:15
    #16
    Wayne Cowdrey
    Olympian Member
    • Total Posts : 965
    • Reward points: 7981
    • Joined: 2007/08/08 12:57:08
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 15:35:06 (permalink)
    0
    Liddy

    Light years is a measurement of Distance rather than time (which some people misunderstand)
    Simply the distance light travels in a year.

    Light travels at 299 792 458 m / s

    Only thing that I know travels faster than the speed of light is subatomic tachyons.
    Gamma is part of the electromagnetic spectrum, therefore travels at the quoted speed of 299 792 458 m / s

    So yea, if it's 3.8 billion light years away, it happened 3.8 billion years ago. 

    But...... I'm often wrong around here lol.

    Hang on a sec... I thought it was impossible for anything to travel faster than the speed of light???
     
    When you say something is x amount of light years away is that how far away it is now or how far away it was when the light left there?
     
    If it's the former then this "event" would have happened more recently than 3.8 billion years ago.
     
    Get what I'm trying to say?
    #17
    theITman
    Pro-Member
    • Total Posts : 4841
    • Reward points: 2228
    • Joined: 2009/12/22 22:25:44
    • Location: Trapped in a box!
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 15:47:12 (permalink)
    0
    No its impossible for anything to accelarate to the speed of light, as its mass would become infinite.
    #18
    Liddy
    Pro-Member
    • Total Posts : 1933
    • Reward points: 4759
    • Joined: 2010/01/10 13:44:11
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 15:56:05 (permalink)
    0
    Yeah I kinda see what you're saying, I mis understood the question, I didn't realise the origin of the radiation was in a galaxy 3.8 million light years away.

    But surely the same principles are present, in the way that they can only observe something happening at a maximum of the speed of light.
    So if they're observing the origin of the radiation surely it happened 3.8billion years ago, unlessss they're observing where the radiation is now, which would be half way as their observation met the radiation half way, so maybe 1.9billion years ago?

    But yeah to actually know how long ago it happened is beyond me. 
    #19
    tac
    Pro-Member
    • Total Posts : 9600
    • Reward points: 8097
    • Joined: 2005/05/13 17:34:06
    • Status: offline
    Re:Physics question - light years and actual time 2011/04/09 19:03:27 (permalink)
    0
    Wayne Cowdrey

    Liddy

    Light years is a measurement of Distance rather than time (which some people misunderstand)
    Simply the distance light travels in a year.

    Light travels at 299 792 458 m / s

    Only thing that I know travels faster than the speed of light is subatomic tachyons.
    Gamma is part of the electromagnetic spectrum, therefore travels at the quoted speed of 299 792 458 m / s

    So yea, if it's 3.8 billion light years away, it happened 3.8 billion years ago. 

    But...... I'm often wrong around here lol.

    Hang on a sec... I thought it was impossible for anything to travel faster than the speed of light???

    When you say something is x amount of light years away is that how far away it is now or how far away it was when the light left there?

    If it's the former then this "event" would have happened more recently than 3.8 billion years ago.

    Get what I'm trying to say?

    how far away when the light left
     
    the origin of the light/radiation/whatever doesnt necessarily even exist anymore, so its impossible to say where it 'is' right now
     
    ie if a star 1000 light years away explodes then it will take us 1000 years to detect that explosion and see the event in our telescopes. By which time the star will no longer exist, and wont have done for a millenia. When you look out into space you are literally looking back in time. Now go smoke a joint and think about that all over again....


    #20
    Page: 12 > Showing page 1 of 2
    Jump to:
    ©2018 All content is copyright of MuscleTalk.co.uk and its use elsewhere is prohibited.
    (posting guidelines | privacy | advertise | earnings disclaimer | contact us | supported by)
    © 2018 APG vNext Commercial Version 5.5