Time

[Grinse]

Just joined, was wondering if I can get some questions answered about time measurement and the application of that measurement.

 

[derekmcd]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Just joined, was wondering if I can get some questions answered about time measurement and the application of that measurement. <br /> Posted by Grinse</DIV></p><p>The only way to find out it to just ask <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" />.&nbsp; Fire away.&nbsp; And welcome to SDC. </p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[Grinse]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The only way to find out it to just ask .&nbsp; Fire away.&nbsp; And welcome to SDC. <br /> Posted by derekmcd</DIV></p><p>&nbsp;</p><p>Yea, very good point.&nbsp;</p><p>&nbsp;</p><p>Well what I was wondering kinda comes in multiple questions. I guess I'll just ask away and see where it goes. and Thank You for the warm welcome!!!</p><p>&nbsp;</p><p>1- When we say 1 year, we mean 365 days to revolve around the sun. My question regarding this is: Does every measurement regarding any type of 'year' refer to our 365 day calendar?</p><p>&nbsp; </p>

 

[Grinse]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Yea, very good point.&nbsp;&nbsp;Well what I was wondering kinda comes in multiple questions. I guess I'll just ask away and see where it goes. and Thank You for the warm welcome!!!&nbsp;1- When we say 1 year, we mean 365 days to revolve around the sun. My question regarding this is: Does every measurement regarding any type of 'year' refer to our 365 day calendar?&nbsp; <br /> Posted by Grinse</DIV></p><p>&nbsp;</p><p>another question I have is in regards to the big bang theory. </p><p>&nbsp;</p><p>If all light started from one source (the big bang) then a star from 50 light years away wouldnt need the 50 light years to reach us right? because the light was always there from the start, or am I wrong?&nbsp; Of course I mean this on a much larger scale.&nbsp;</p><p>&nbsp;</p><p>what I mean is can we measure the age of a universe just from light? If the big bang is fact I dont see how it's a viable measurement tool.&nbsp; </p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp; </p>

 

[derekmcd]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Yea, very good point.&nbsp;&nbsp;Well what I was wondering kinda comes in multiple questions. I guess I'll just ask away and see where it goes. and Thank You for the warm welcome!!!&nbsp;1- When we say 1 year, we mean 365 days to revolve around the sun. My question regarding this is: Does every measurement regarding any type of 'year' refer to our 365 day calendar?&nbsp; <br /> Posted by Grinse</DIV></p><p>The International Astronomical Union (IAU) defines a year at 365.25 days.&nbsp; To define the distance light travels in one year, you multiply the speed of light (299,792,458 m/s) * 31,557,600 seconds (number of seconds in a year).</p><p>These numbers are rounded and you can actually get more precise then this should the need arise. </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[derekmcd]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;another question I have is in regards to the big bang theory. &nbsp;If all light started from one source (the big bang) then a star from 50 light years away wouldnt need the 50 light years to reach us right? because the light was always there from the start, or am I wrong?&nbsp; Of course I mean this on a much larger scale.&nbsp;&nbsp;what I mean is can we measure the age of a universe just from light? If the big bang is fact I dont see how it's a viable measurement tool.&nbsp; &nbsp;&nbsp;&nbsp; <br /> Posted by Grinse</DIV></p><p>The light (or more precisely, the electromagnetic radiation) arises from interactions of the atoms of the source.&nbsp; Photons did not arise from a single source ((unless you are referring to the Cosmic Microwave Background Radiation (CMB)).</p><p>Essentially, the photons from a star 50 light years distance are created in real time and do, indeed, need 50 million years to reach us. </p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[Grinse]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The light (or more precisely, the electromagnetic radiation) arises from interactions of the atoms of the source.&nbsp; Photons did not arise from a single source ((unless you are referring to the Cosmic Microwave Background Radiation (CMB)).Essentially, the photons from a star 50 light years distance are created in real time and do, indeed, need 50 million years to reach us. <br /> Posted by derekmcd</DIV></p><p>Good stuff man. I have more Q's just need some time.&nbsp; </p>

 

[derekmcd]

I'd just like to add that things get a bit trickier when you are talking about cosmological distances.&nbsp; Fifty million light years is rather short.&nbsp; However, when you start talking about distances of of say one billion light years (1 gly), you have to factor in the expansion of space and comoving coordinates to define light travel time. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[Grinse]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'd just like to add that things get a bit trickier when you are talking about cosmological distances.&nbsp; Fifty million light years is rather short.&nbsp; However, when you start talking about distances of of say one billion light years (1 gly), you have to factor in the expansion of space and comoving coordinates to define light travel time. <br />Posted by derekmcd</DIV></p><p>&nbsp;I understand the vast distances and all. What I have trouble with is our method of measurement. We basically measure all things by our own standards. Our 1 mile is just over 5100 feet, we base a year on 365 days or 1 revolution around OUR sun. So in essence we base all measuring tools that we use for space on our own measuring system. It just seems rather wrong to me. </p><p>&nbsp;My age, your age, everyones age is based on revolutions around our son. What if we revolve around our sun rather quickly? what is the basis of our measurement? How do we know 1m light years is an exetremely long time?&nbsp; or can it be extremely short? afterall any measurement is based on our revolution around our sun.</p><p>&nbsp;I guess my question is this. </p><p>&nbsp;Is our perception of time valid? How do we know 1m years is really that significant? Between you and I yes it is very significant. But between me and the universe...is it that significant? 1m years is 1m earth revolutions around our sun, according to us, thats long, but what about the universe?</p><p>&nbsp;</p>

 

[derekmcd]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I understand the vast distances and all. What I have trouble with is our method of measurement. We basically measure all things by our own standards. Our 1 mile is just over 5100 feet, we base a year on 365 days or 1 revolution around OUR sun. So in essence we base all measuring tools that we use for space on our own measuring system. It just seems rather wrong to me. &nbsp;My age, your age, everyones age is based on revolutions around our son. What if we revolve around our sun rather quickly? what is the basis of our measurement? How do we know 1m light years is an exetremely long time?&nbsp; or can it be extremely short? afterall any measurement is based on our revolution around our sun.&nbsp;I guess my question is this. &nbsp;Is our perception of time valid? How do we know 1m years is really that significant? Between you and I yes it is very significant. But between me and the universe...is it that significant? 1m years is 1m earth revolutions around our sun, according to us, thats long, but what about the universe?&nbsp; <br /> Posted by Grinse</DIV></p><p>The units you choose to use are really arbitrary.&nbsp; What's important is that you maintain consistency when applying those units.&nbsp; The physics behind the formulae remain the same.&nbsp; The speed of light in a vacuum could careless what units we apply to it.&nbsp; We simply use units that we can easily understand.</p><p>Is 1myr significant compared to the age of the universe?&nbsp; I'll let you decide that.&nbsp; Considering the universe is estimate to be 13.7 gyr (according to Big Bang cosmology and the LamdaCDM model), 1 myr doesn't seem all that much.&nbsp; I'll round up to 14 gyr.&nbsp; One million years is 1/14000th or ~.00007.&nbsp; One million years would have to elapse 14,000 times.&nbsp; In human terms, let's use the age of a 100 year old person.&nbsp; This would be the equivelant of around 2.5 days old.</p><p>It's all relative and arbitrary.&nbsp; What's important are the physics behind the formulae and the conclusions we draw from them. </p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[Grinse]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The units you choose to use are really arbitrary.&nbsp; What's important is that you maintain consistency when applying those units.&nbsp; The physics behind the formulae remain the same.&nbsp; The speed of light in a vacuum could careless what units we apply to it.&nbsp; We simply use units that we can easily understand.Is 1myr significant compared to the age of the universe?&nbsp; I'll let you decide that.&nbsp; Considering the universe is estimate to be 13.7 gyr (according to Big Bang cosmology and the LamdaCDM model), 1 myr doesn't seem all that much.&nbsp; I'll round up to 14 gyr.&nbsp; One million years is 1/14000th or ~.00007.&nbsp; One million years would have to elapse 14,000 times.&nbsp; In human terms, let's use the age of a 100 year old person.&nbsp; This would be the equivelant of around 2.5 days old.It's all relative and arbitrary.&nbsp; What's important are the physics behind the formulae and the conclusions we draw from them. <br /> Posted by derekmcd</DIV></p><p>&nbsp;</p><p>Awesome, thanks again. Need to think </p>

 

[MeteorWayne]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Awesome, thanks again. Need to think <br />Posted by Grinse</DIV><br /><br />The base unit of measurement is the second; everything else is derived from that. It used to be defined based on the earth's day (1/86400 of the mean solar day), but since that constantly changes, it has now been redefined to a fixed amount of time:</p><p><strong>Under the International System of Units, the second is currently defined as</strong></p><blockquote><div><p><strong>The second is the duration of <span style="white-space:nowrap">9 192 631 770</span> periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.<sup class="reference"><span>[</span>1<span>]</span></sup></strong></p></div></blockquote><p><strong>This definition refers to a cesium atom at rest at a temperature of 0 </strong><strong>K</strong><strong> (</strong><strong>absolute zero</strong><strong>), and with appropriate corrections for </strong><strong>gravitational time dilation</strong><strong>. The ground state is defined at zero </strong><strong>magnetic field</strong><strong>. The second thus defined is consistent with the ephemeris second, which was based on astronomical measurements.</strong></p><p>There are several definitions for a year, which last slightly different amounts of time, but all are very close to 365.24 days.</p><p>But it all comes back to the second, which is based in an invariate physical principle.</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>