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Author Topic: Did the universe expand faster in the past?  (Read 1368 times)

Tom Ristola

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Did the universe expand faster in the past?
« on: 21/11/2011 20:30:03 »
Tom Ristola asked the Naked Scientists:
   
Hi

Having some trouble understanding the interpretation of the observations that have been made of the expanding universe.

With more galaxies appearing to be more red-shifted the further away they are, they appear to be moving faster the further away they are.  Since the further away you look, the further back in time you are looking, are we not really seeing that the expansion was faster earlier in the history of the universe?  

Tom Ristola
Edinburgh

What do you think?
« Last Edit: 21/11/2011 20:30:03 by _system »


 

Offline yor_on

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Did the universe expand faster in the past?
« Reply #1 on: 21/11/2011 22:48:40 »
That's a really neat idea Tom, maybe, but there are no evidence that I know of?
 

Offline Phractality

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Did the universe expand faster in the past?
« Reply #2 on: 22/11/2011 05:54:20 »
At present, the rate of expansion is about 2.5 x 10^-18/s. If it had always been that rate, distances would have been half what they are today 9 billion years ago, and 1/8 as far 27 billion years ago. Big bang theory puts the age of the universe at just 13.7 billion years. Supposedly, there was a period of extremely rapid expansion (called inflation) before it slowed down. Now, it appears to be speeding up again.

If you ask me, the numbers for the inflationary big bang theory don't make sense.

Calculation: (1 + 2.5 x 10^-18)^(9000000000 years/ 1 second)≈ 2.

 
(With Wolframalpha, you have to use 2.50000000001 to tell it to use extra prescision; otherwise you get 1 instead of 2. I'm actually working the problem backwards after solving it. If you start with 2 and work the problem forewards to get 9 billion years, you have to use logarithms.) 

The type 1a supernova data are comparing the brightness to the redshift. If the expansion were constant, twice the redshift would correspond to 1/4 the brightness. Instead, it the brightness is slightly greater than that. Note that they are using comoving distance. If you don't understand comoving distance, you won't understand the results.
« Last Edit: 22/11/2011 06:03:14 by Phractality »
 

Offline yor_on

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Did the universe expand faster in the past?
« Reply #3 on: 26/11/2011 17:07:23 »
You know, it's a really good idea actually, and it keep on bothering me :) The idea of an expansion is coupled to what we call 'dark energy'.

"in 1996, observations of very distant supernovae required a dramatic change in the picture. It had always been assumed that the matter of the Universe would slow its rate of expansion. Mass creates gravity, gravity creates pull, the pulling must slow the expansion. But supernovae observations showed that the expansion of the Universe, rather than slowing, is accelerating.

Something, not like matter and not like ordinary energy, is pushing the galaxies apart. This "stuff" has been dubbed dark energy, but to give it a name is not to understand it. Whether dark energy is a type of dynamical fluid, heretofore unknown to physics, or whether it is a property of the vacuum of empty space, or whether it is some modification to general relativity is not yet known."

Your idea seems a logical approach to what we see, as those stars furthest away will be closer to the 'inflationary period'. But it doesn't fit the definition we have of the inflationary period. The evidence for a inflation is thought to lie in the way the Cosmic microwave radiation exists in the universe.

"This faint radiation permeates the entire observable universe—evidence that it was present early on, about 400,000 years after the birth of the universe. The other striking aspect of the CMB is its remarkably consistent temperature. The simplest explanation is that at some point the entire universe was small enough to be at thermal equilibrium. "I like to think of finding pieces of a hot potato scattered around a house," says Lee. "All of those pieces are the same temperature. The logical conclusion would be that they all belonged to the same potato, and that someone heated that potato, cut it up, and spread the pieces from room to room."

Lee has engineered a way to miniaturize and mass produce the photon detectors needed to obtain signals about primordial gravitational waves. He can now fit 1,000 detectors, called bolometers, onto a 9" x 9" silicon wafer. Minute variations in the temperature of the CMB were found in the early 1990s by George Smoot of UC Berkeley and John Mather of NASA Goddard Space Flight Center. They won the 2006 Nobel Prize in physics partly for this work. "

The next step will be to try to measure the 'foot prints' in the sky of those gravitational waves originating at the Big Bang. "If inflation occurred, it would have created ripples in the fabric of space-time called gravitational waves. These waves should have etched a distinctive pattern into the CMB. "Imagine you're looking at the sky with eyes that can see microwaves, but you're also wearing polarized sunglasses. If you looked from place to place, you'd see faint fluctuations in the polarization intensity of the sky. If you could see the lines of the polarization, you would see that they are pointing in different directions in different points of the sky," Lee says.

The patterns would resemble the lines of force around a magnet, or the celestial gyres depicted in Vincent Van Gogh's painting Starry Night. "If we see these swirling patterns of vectors, they would be a smoking gun that inflation occurred," Lee says. But detecting these patterns will be astoundingly difficult. The signals are very faint—a difference of billionths of a degree atop the 2.7 Kelvin of the CMB."

From Evidence for Inflation

The next question should be why we place it so early, before the universe started to make matter.

"One difficulty in answering this question is that inflation was over well before recombination, and so the opacity of the Universe before recombination is, in effect, a curtain drawn over those interesting very early events. Fortunately, there is a way to observe the Universe that does not involve photons at all. Gravitational waves, the only known form of information that can reach us undistorted from the instant of the Big Bang, can carry information that we can get no other way. Two missions that are being considered by NASA, LISA and the Big Bang Observer, will look for the gravitational waves from the epoch of inflation." From The Big Bang.

So, have they found any evidence for those gravitational waves/imprints on the sky? Well, experiments are still ongoing, as I understands it. Looking for gravitational waves in a sea of noise.

And here is a rather interesting comment, especially as 'supersymmetry' is losing ground according to some results at Cern, if I remember right? But I don't know really, maybe even the standard model will have to be redefined if there's no Higgs bosons or 'fields' found? It's really interesting times. Does physics win if Hawking loses bet?
=

Had to 'clean it' somewhat.
« Last Edit: 26/11/2011 17:22:11 by yor_on »
 

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Did the universe expand faster in the past?
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