Timeline for Inflation and the Meaning of Time
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
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| Mar 27, 2014 at 0:46 | comment | added | Kyle Oman | @Jim The distance between them expands faster than the speed of light, yes, but this is allowed. It's just spacetime expanding very fast, which is allowed. It's motion THROUGH spacetime (by objects or photons) that is capped at $c$. It can be a bit hard to disentangle the two at first. You can try thinking in "comoving coordinates". This coordinate system is defined by always re-scaling distances by the size of the universe (relative to it's size of 1.0 today). In this coordinate system, there is no expansion, so the "speed limit" is intuitive: distances between objects cannot grow at >$c$. | |
| Mar 26, 2014 at 23:03 | comment | added | Jim | @Kyle Rather than taking the point of view of the photon, what about two objects separated by some distance (space) before inflation. (I don't know what those objects would be at this point in the timeline, but I want to assume they are real and not abstract, like a hypothetical comoving observer might be.) If space expands faster than the speed of light, wouldn't the distance between these objects separate at a speed faster than light? | |
| Mar 26, 2014 at 22:54 | history | edited | Kyle Oman | CC BY-SA 3.0 |
corrected typo
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| Mar 26, 2014 at 18:15 | comment | added | Kyle Oman | @PeterMichealLacey-Bordeaux constants most certainly have units (well, when it's relevant anyway). $c$ has units of length/time, and indeed is crucial to the dimensional validity of the metric. You can do all sorts of trickery to shuffle around the dimensions, re-express constants as dimensionless, set them equal to 1 and not worry about dimensions if you know what you're doing, and so on. But generically (some) constants do have units. | |
| Mar 26, 2014 at 18:11 | history | edited | Kyle Oman | CC BY-SA 3.0 |
corrected typo in metric
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| Mar 26, 2014 at 18:11 | comment | added | Kyle Oman | @Jim Ah yes, that should be a $c^2$. My mistake. | |
| Mar 26, 2014 at 18:05 | comment | added | placeybordeaux | @Jim c is a constant, so there are no units attached to it. | |
| Mar 26, 2014 at 17:48 | comment | added | Jim | While I'm pondering the information here, shouldn't that be c-squared, to keep the units consistent? (Maybe you're just checking to see if I'm paying attention :) ) | |
| Mar 26, 2014 at 16:47 | history | answered | Kyle Oman | CC BY-SA 3.0 |