Catch me if you can

[kabtn05]

In this article:<br />http://www.space.com/scienceastronomy/big_rip_030306.html <br />Robert Roy Britt quotes Loeb as saying, "Eventually, galaxies will recede at the speed of light, making it impossible for their light -- or any other radiation or information -- to traverse the cosmos to our home in the Milky Way Galaxy…Any given source accelerates away from us and eventually reaches a speed larger than the speed of light so that photons emitted from it cannot catch up with the cosmic expansion, relative to us.”<br /><br />So, I wanted to ask you about something. Please allow me to illuminate my ignorance. Assume the emission of light, radiation and information of galaxy A has – and will have for its existence – a clear, uninterrupted path or view of earth. Assume galaxy A and earth are moving apart faster than the speed of light (btw, is that really possible).<br /><br />It seems mathematically sound to say the emissions of galaxy A will never reach earth. This is Conclusion A. But is it the most mathematically correct conclusion? I ask this weird question because we’re dealing with something headed towards earth that will NEVER be interrupted. “Never” being infinite time. How can we evaluate infinity? Can we evaluate it to an absolute? (I’ve never heard of that.) This makes me believe you can not rule out the possibility that the emissions will reach earth. Call this Conclusion B.<br /><br />OK, so I’m confused. Can both be right? It looks like there are two different but correct mathematical expressions/answers for one truth (I know there’s a better word than truth).<br /><br />And if so (time for another ignorant question), do we have mathematical equations that take this into account? Are there equations built around Conclusion B that help us study the universe?<br /><br />Pi cannot come to an end but we’ve quantified it enough to use it in useful mathematical ways.

 

[vogon13]

And while you're waiting for that ray of light to reach earth, in 10^33 years, all the protons in our region of the universe will have decayed away, so it is kind of a moot point whether the ray of light ever gets here. And it might approach from the opposite direction, first, too.<br /><br />In the big cosmic scheme of things, we don't amount to a hill of beans.<br /><br />Here's lookin' at you...... <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[newtonian]

kabtn05 - First, I consider your question about forever valid, unlike vogon13.<br /><br />Proton decay and various transmutations of matter, and conversions between matter and energy, will not bring an end to matter in our universe, and the Bible simply states that earth will be inhabited forever (e.g. Psalms 37:29; etc.).<br /><br />Consider, for example, the law of conservation of matter and energy.<br /><br />Also, I don't accept the balloon model.<br /><br />However, while there is a speed limit for matter on the fabric of space, which is at this time c, the speed of light, we are not aware of a speed limit for the actual expansion of the fabric of space.<br /><br />That is why galaxy A could be moving away from earth and Milky Way FTL (faster than light).<br /><br />Note, btw, that photons can be reflected - and light can change direction - compare gravitational lensing of light.<br /><br />Reflected light can reach an object that is within our visibility horizon from a source beyond our visibility horizon.<br /><br />For example, a galaxy moving 10% FTL will still be within the light cone of an object moving 50% of the speed of light from earth. <br /><br />Said reflected photon then could eventually reach earth via that reflector which is within our light cone.<br /><br />Stated simply, light cones can overlap.<br /><br />This is the basis of one of my theories: that acceleration of expansion is being caused by gravitational effects from beyond our light cone or visibility horizon from FTL receeding matter which is nonetheless within the light cone of distant galaxies near but within our visibility horizon (aka light cone) - a sort of domino effect.

 

[larper]

Ignore Newtonians gibberish. <br /><br />What happens is that the photons are infinitely redshifted. Their wavelength becomes infinitely long and they basically cease to be photons at all. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

 

[newtonian]

larper - Oh really? So what do photons become when they cease to be photons.<br /><br />And you can ignore overlapping light cones if you wish.<br /><br />Or you could try doing a little research.

 

[kabtn05]

Thank You all of you. I learn from reading your posts and replies. In college my Physics teacher did post doctorate work with black holes. She was from China and brilliant, but a little to brilliant to teach basic physics. I failed her class. I knew I wasn't totily dum thow. I learn more from this website.

 

[newtonian]

kabtn05 - You are welcome. There was a very interesting article on light cones in Scientific American not too long ago. <br /><br />I will try to locate and post an excerpt.<br /><br />No one, however, has taken the next step which I did - to my knowledge - then again, I am not aware of what many other scientists are theorizing on this.

 

[the_masked_squiggy]

Interesting question. First off, I don't think I'm qualified enough on the subject to give you a definitive answer--<br /><br />but first, if we're moving away from something at the speed of light, and the photons emitted are traveling at the speed of light, then I'm guessing they'll never reach us. They'll always remain as far away from us as they were when they were emitted. In other words, the photon will chase us, but not catch up. We'll never be able to see it, because as far as we're concerned, it's infinitely redshifted. <br /><br />Next, if an object going really fast away from us emits a photon, we see it as really redshifted. If the object is moving away at the speed of light and emits a photon in the opposite direction of its travel, the photon will be infinitely redshifted, and be a "frozen image" because of time dilation when things approach c. Same phenomenon as light entering a black hole: the light gets more and more redshifted and as it becomes infinitely redshifted it appears to "freeze" on the event horizon.<br /><br />Thanks to Saiph for a nudge in the right direction on the second one there.<br />

 

[heyscottie]

katbn05:<br /><br />Think of it this way.<br /><br />If two galaxies are moving apart from one another at faster than the speed of light (which IS presumed to be possible in a rapidly expanding space-time, by the way), we can take either one to be the "stationary" one.<br /><br />So, galaxy A and galaxy B are moving away from each other at 1.5*c (and always getting faster, too).<br /><br />Galaxy A shoots light at galaxy B. This light, of course, travels at c. Sadly, galaxy B is moving away faster than the light is travelling toward it, so the light never gets there.<br /><br />Looking the other way, we could say that galaxy A is moving away faster than the speed of light, and B is stationary, so the light from B could never get to A, either.<br /><br />This covers all the cases. It is possible to look at it in another way, though too.<br /><br />Let galaxy A be not moving and galaxy B be moving faster than the speed of light. B's light should still get to A sometime, right? Well, no. The reason is due to redshift. At luminal (and superluminal) separation speeds, any light will be infinitely red-shifted. It doesn't even exist for galaxy A. So it never gets there, and galaxy B has disappeared forever.<br /><br />Scott

 

[kabtn05]

Very Cool. Well, then is it possible that we see light from galaxies that don't even exist anymore? Sorry for stupid questions...they come natural for me.

 

[newtonian]

kabtn05 - Yes, that is certainly possible.<br /><br />Or they may still exist but in greatly modified form after mergers with other galaxies - that is more likely.<br />And, as Loeb notes, they may now be beyond our light cone! <br /><br />Sorry, I haven't found that article yet. <br /><br />Time constraint - speaking of time (c, light speed, involves time; and seeing distant galaxies is seeing back in time).