<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>"Space" does not expand in GR theory, only in Lambda theory. GR theory only explains the expansion of "spacetime" as the physical objects that make up spacetime move away from each other and 'expand" at subluminal speeds. You neglected to ever show that "space" actually expands in any emprical test, so any introduction of constants into GR are "Lambda" theories, not GR theories. Let's keep these ideas clear, otherwise the conversation will never make any sense to anyone. If you going to talk about "expanding space", please do not refer to this as "GR". It's not. It's a variation of Einstein's "blunder" theory, not GR.<br /> Posted by michaelmozina</DIV></p><p>We've had this discussion before. I forgot that you are incapable of making the distinction between objectifying space as a physical entity and referring to space as a nothing more than a distance. There's a reason it is called the <em><strong>metric</strong></em> expansion of space.</p><p>Generally speaking, when discussing this subject with other knowledgeable folks, it is perfectly acceptable to say space is expanding. It is assumed that the knowledgeable person you are discussing it with does not consider space as a physical entity. </p><p>If I were to introduce some 10th grade students to expansion, I would NOT initially refer to it as "space is expanding" so they would not objectify it and consider a material "thing". I would make it quite clear that it is the distance between two objects that are increasing. I would make them understand that "space" is nothing more than the distance between two objects that you measure with a ruler and it is the function of distance (metric) that is expanding. </p><p>I might site an example of, "How much space is there between science classroom and your english classroom?" You measure that space with a ruler. Now, if the school is analogous to space and we expand the school, the distance between the classrooms increase.</p><p>I would then ask them, "What physically expanded?" They might respond, "The school expanded". I would explain to them that the school is nothing more than a collection of classrooms (galaxies) within the school (space). Technically, nothing physically expanded... only the distance between the classrooms were increased.</p><p>When this becomes clear to them, only then is it safe to use the shorthand terminology of the expansion of space. </p><p>Space, when defined as a metric, in the case of the FLRW metric can, in fact, expand. To say "<strong>"<em>Space" does not expand in GR theory, only in Lambda theory</em></strong>", as you succinctly put it, shows a clear misunderstanding of what is really happening. </p><p>When you say, "<strong><em>GR theory only explains the expansion of "spacetime</em>" <em>as the physical objects that make up spacetime move away from each other and 'expand" at subluminal speeds</em></strong><strong>"</strong>, only magnifies your complete misunderstanding. </p><p>First, how can spacetime expand? Do you even understand what spacetime is? Spacetime is really nothing more than a collective way to describe events based on four coordinates... the three of space and one of time. Events happen in spacetime.</p><p>And, as a side note, SUPERluminal speeds are a direct consequence of the Hubble Constant and do not violate Special Relativity. Your injection of SUBluminal speeds is just plain silly... especially from one claiming to understand either of the Relativities. </p><p> </p><p>If any of my interpretations above are incorrect, I welcome any corrections or clarifications. I don't profess to know much about General Relativity and all the manifolds, tensors, metrics and such, but I've read enough that I know how to differentiate some of the terminology and think I understand the underlying basics of it.<br /> </p><p>For someone that claims to have been taught General Relativity in a University, I really question what it was that you were taught or how much of it you actually learned. </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>