# Universe inflation faster than c

#### norvegicusbas

The current theory regarding the beginning of the universe insists that there was a brief period of inflation where the growth of the universe out paced the speed of light growing to light years in diameter in a few minutes. How is it possible?

#### JesseM

The current theory regarding the beginning of the universe insists that there was a brief period of inflation where the growth of the universe out paced the speed of light growing to light years in diameter in a few minutes. How is it possible?
There's nothing special about the inflationary period in this sense, even today galaxies sufficiently distant from us have a "speed" greater than c according to [URL [Broken] law[/url]. However this is only "speed" relative to a particular definition of cosmological distance and time, which are different from "speed" defined in distance/time in an inertial frame (see the wikipedia page on comoving distance and proper distance, in particular the third paragraph in this section which discusses the meaning of FTL recession velocities). Even in special relativity where there is no expansion of the universe, the rule that objects cannot travel faster than c, and that light itself always moves at c, does not apply if we are talking about coordinate speed in a non-inertial coordinate system such as Rindler coordinates.

You may also be interested in reading the Scientific American article http://www.scientificamerican.com/article.cfm?id=misconceptions-about-the-2005-03 [Broken], which discusses issues surrounding FTL recession velocities on p.3 and 4.

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#### JJRittenhouse

The current theory regarding the beginning of the universe insists that there was a brief period of inflation where the growth of the universe out paced the speed of light growing to light years in diameter in a few minutes. How is it possible?
Space expands uniformly, which is to say, every part of space expands at the same rate. The more space between two objects, the more space you have to expand at a constant rate (at every point in space). The further two objects are from each other, the faster space between them expands. Locally, gravity overcomes this force, so stars in our galaxy aren't moving away from us due to this, and Andromeda is still going to obliterate our galaxy when it comes rolling into us.

If there is sufficient distance between two objects so that the attractive effect of gravity is insignificant, then as space expands, they will appear to move faster and faster away from each other.

However, they aren't actually "moving", and neither is space, space is simply "getting inserted" between them, so there is no violation of velocity. (actually expanding, but "expanding" gives me the impression that pressure from expanding space is pushing on two bodies, and that isn't really what is happening. There is just more space between them, so, inserting the space kind of illustrates it better)

#### tom.stoer

For a comprehensive summary please refer to the following paper

http://arxiv.org/abs/astro-ph/0310808
Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the UniverseTamara M. Davis, Charles H. Lineweaver
(Submitted on 28 Oct 2003 (v1), last revised 13 Nov 2003 (this version, v2))
Abstract: We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the Universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard Lambda-CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the observable universe'' and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23 sigma.

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