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"Speed of Light"
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<blockquote data-quote="freyar" data-source="post: 6278158" data-attributes="member: 40227"><p>FTL motion is not possible in our best understanding of physics, and it would take a truly revolutionary and unexpected discovery to change that.</p><p></p><p>The phrase "a burst of inflation that was seemingly faster than the speed of light" is possibly one of the most misleading and damaging that people can use when talking about the expansion of the universe. If a scientist said it, they either didn't know the subject, were being incredibly lazy in talking to the press, or weren't thinking. And, in this case, the "FTL mistake" doesn't even require inflation. Here's my explanation:</p><p></p><p>The expansion of the universe does not entail the motion of objects. If I have two far-enough-apart galaxies, <em>they stay in the same places</em> and <em>space appears between them</em>. This does create the Doppler effect on light from one galaxy going to the other. If you didn't know better, you'd think they were moving apart, but of course we at EN World know better now. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink ;)" loading="lazy" data-shortname=";)" /> So saying that the expansion of the universe involves FTL motion involves the mistake of thinking things are moving. It involves a simpler mistake, too: even if you think the galaxies are actually moving apart, you only see "FTL" motion if you use the simplified formula for the Doppler effect which <em>only</em> works for speeds much smaller than the speed of light! Using the correct relativistic formula never gives FTL speeds.</p><p></p><p>And there's one other problem with that phrase in this context: if you make <em>both</em> mistakes and think there is FTL motion due to the expansion of the universe, you don't have to go all the way back to cosmic inflation to do that. Some of the farther away galaxies we see would appear to be moving FTL. No matter how fast the universe is expanding, you can always see "FTL motion" if you just look far enough away. That's a feature of the expansion of space itself. You don't need inflation.</p><p></p><p>BTW, <a href="https://www.enworld.org/index.php?threads/353683/" target="_blank">there's another thread</a> on this subject.</p></blockquote><p></p>
[QUOTE="freyar, post: 6278158, member: 40227"] FTL motion is not possible in our best understanding of physics, and it would take a truly revolutionary and unexpected discovery to change that. The phrase "a burst of inflation that was seemingly faster than the speed of light" is possibly one of the most misleading and damaging that people can use when talking about the expansion of the universe. If a scientist said it, they either didn't know the subject, were being incredibly lazy in talking to the press, or weren't thinking. And, in this case, the "FTL mistake" doesn't even require inflation. Here's my explanation: The expansion of the universe does not entail the motion of objects. If I have two far-enough-apart galaxies, [I]they stay in the same places[/I] and [I]space appears between them[/I]. This does create the Doppler effect on light from one galaxy going to the other. If you didn't know better, you'd think they were moving apart, but of course we at EN World know better now. ;) So saying that the expansion of the universe involves FTL motion involves the mistake of thinking things are moving. It involves a simpler mistake, too: even if you think the galaxies are actually moving apart, you only see "FTL" motion if you use the simplified formula for the Doppler effect which [I]only[/I] works for speeds much smaller than the speed of light! Using the correct relativistic formula never gives FTL speeds. And there's one other problem with that phrase in this context: if you make [I]both[/I] mistakes and think there is FTL motion due to the expansion of the universe, you don't have to go all the way back to cosmic inflation to do that. Some of the farther away galaxies we see would appear to be moving FTL. No matter how fast the universe is expanding, you can always see "FTL motion" if you just look far enough away. That's a feature of the expansion of space itself. You don't need inflation. BTW, [URL="https://www.enworld.org/index.php?threads/353683/"]there's another thread[/URL] on this subject. [/QUOTE]
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