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Light year distance question
I've recently read that a distant galaxy 11 billion light years away
has been spotted. Does this mean that in actuality it was 11 billion light years away 11 billion Years ago or that it is that far away now? If it was 11 billion light year away 11 billion years ago then how can this be the case assuming the universe is 14 billion years old. Each galaxy would have had to travel 5.5 billion light years in just three billion years i.e. moving faster than the speed of light? This is assuming they originated in the same place as per the big bang theory. Please let me know if I'm way off the mark here, just interested to know. Tony Sims |
#2
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Light year distance question
Tony Sims wrote:
I've recently read that a distant galaxy 11 billion light years away has been spotted. Does this mean that in actuality it was 11 billion light years away 11 billion Years ago or that it is that far away now? If it was 11 billion light year away 11 billion years ago then how can this be the case assuming the universe is 14 billion years old. Each galaxy would have had to travel 5.5 billion light years in just three billion years i.e. moving faster than the speed of light? This is assuming they originated in the same place as per the big bang theory. Please let me know if I'm way off the mark here, just interested to know. Tony Sims Hmmm, this has gotten me the thinking. Givens: Age of Universe, since Big Bang; 14 Billion Years. Distance from Earth of Observed Galaxy; 11 Billion Light Years. OK, the light we observe from this Galaxy (I'll call it G1) has been traveling for 11 Billion years. "Eleven Builliyon Years" to quote Carl Sagan. At the time the light we now observer was generated G1 was 11B Light Years away. In the time it took to get here G1 was continued to move. So, how far away _IS_ G1? TBerk |
#3
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Light year distance question
It means that light from that galaxy has taken 11 billion years to reach us.
Every second light travels approximately 186,000 miles, which makes the galaxy 11,000,000,000 * 186,000 * 60 * 60 * 24 * 365 miles away. I tried to work it out on my calculator, but it screamed and hid behind the sofa! Since the universe is expanding, it used to be closer. How close? well, one as close as these two dots .. if all the theories are correct. "Tony Sims" wrote in message om... I've recently read that a distant galaxy 11 billion light years away has been spotted. Does this mean that in actuality it was 11 billion light years away 11 billion Years ago or that it is that far away now? If it was 11 billion light year away 11 billion years ago then how can this be the case assuming the universe is 14 billion years old. Each galaxy would have had to travel 5.5 billion light years in just three billion years i.e. moving faster than the speed of light? This is assuming they originated in the same place as per the big bang theory. Please let me know if I'm way off the mark here, just interested to know. Tony Sims |
#4
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Light year distance question
T wrote in message .com...
Tony Sims wrote: So, how far away _IS_ G1? Well we don't measure how long it takes the light to travel. Its based on the observed data (ie red shift, and the current Hubble constant or type 1a supernova?), from this we estimate how far away it is more or less now. IIRC.. |
#5
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Light year distance question
(Tony Sims) wrote in message . com...
I've recently read that a distant galaxy 11 billion light years away has been spotted. Does this mean that in actuality it was 11 billion light years away 11 billion Years ago or that it is that far away now? If it was 11 billion light year away 11 billion years ago then how can this be the case assuming the universe is 14 billion years old. Each galaxy would have had to travel 5.5 billion light years in just three billion years i.e. moving faster than the speed of light? This is assuming they originated in the same place as per the big bang theory. Please let me know if I'm way off the mark here, just interested to know. Tony Sims Well, you've asked a number of questions. The first, is how do astronomers know how far away the object is. The answer is, they just measured the Z of the object - its relativistic doppler shift. That's all. This is described elegantly at the following URL http://hyperphysics.phy-astr.gsu.edu...v/reldop2.html And you can check out the high-red-shift quasar here; http://antwrp.gsfc.nasa.gov/apod/ap981211.html These are some 15 billion light years from Earth. The Z's are on the order of 5. Taking our equation we can see the relation between Z and speed of light; Z = SQRT((c+v)/(c-v)) - 1 And distance is given by the Hubble constant which astronomers believe is between 16 km/sec and 25 km/sec per million light years. Let's take the average of 20.5 km/sec per million light years. That's equal to 0.006833% per million light years. So, to produce a Z=5 requires a v=283,800 km/sec or v=94.6% the speed of light. Dividing by 20.5 km/sec per million light years or 0.006833% obtains a distance of 13,843,902,000 light years. That's pretty far away. How big is the universe today? Well if you put a v=c in the Z calculation, you'll find that Z becomes infinite, but distance does not. With the hubble constant given the universe is 14.634 billion light years in diameter. The Hubble constant gives the size of the universe. If its smaller (16 km/sec per million light years) the universe is 18.75 billion years across and years old. If its larger (25 km/sec per million light years) the universe is 12.00 billion light years across and years old. The second part of your question deals with things in motion relative to one another. In this regard its important to note that the speed of light is constant for all observers and that light does not pass for the photon. In fact the light ray that connects an observer to an object is known to physicists and astronomers as the null-time path. All light rays leaving an object in all directions at a particular instant create what is known as a lightcone surrounding that instant in their minkowski, or 4D space time, or hyperspace representation (these all mean the same thing). In this context its important to note that the assumption here (which is in the process of changing given even more detailed analysis of new data from Hubble and COBE and elsewhere) is that if something is moving at 94.6% the speed of light now, it was moving at 94.6% the speed of light 14.634 billion years ago. That's the way everything comes back to a precise point at the beginning of time. Now, you may recall that one part of relativity is the twin paradox. That's where a twin moving rapidly in space relative to a twin living at home ages more slowly than the stay at home twin. The interesting thing is that BOTH twins observing one another with a telescope observe the OTHER TWIN aging more slowly. Your question revolves around your trouble with this paradox. Which will require another ton of explanation... if you are unaware of it, let me know, I'll take it offline with you! |
#6
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The current distance to the most distant object we can see is 46 billion light years. But we are seeing it as it was a long time ago and I doubt if we will ever see the light it is sending now. Better read it yourself. |
#7
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I've recently read that a distant galaxy 11 billion light years
away has been spotted. Does this mean that in actuality it was 11 billion light years away 11 billion Years ago or that it is that far away now? This is a little complicated, which probably explains why there have been so many incomplete or wrong answers. Part of the problem is that there are several different definitions of "distance" that are important in cosmology. Probably the best resource for questions of this type is Ned Wright's Javascript "cosmology calculator" at http://www.astro.ucla.edu/~wright/CosmoCalc.html The calculator has links to explanations of the concepts involved. By the way, the Doppler formula does not give correct answers although it gives qualitatively the correct behavior that distance is finite at infinite redshift. If you put in the current favorite cosmology parameters H_0 = 71, Omega_M=0.27 and a guess for redshift z=2.5 and push 'Flat', you find a light travel time of 11 Gyr. This corresponds to a current comoving radial distance of 19.3 billion light years. That is to say, if the light left the galaxy 11 billion years ago and if you could measure the distance away it is "now," you would find 19.3 billion light years. Of course it will take 19.3 billion years for the light that galaxy is emitting "now" to reach us. (I put "now" in quotes because time is complicated, but you can think of "now" as meaning the epoch when the microwave background temperature is 2.73 K.) It's hard to tell from something as vague as a press release, but this was probably the intended meaning. If instead you put in z=1.02, you find a comoving radial distance of 11 billion light years and a light travel time of 7.8 billion years. This meaning is also a possible interpretation. |
#8
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