Fermilab Reports Dark Energy Not Needed

An anonymous reader writes "A Fermilab press release reports that the expansion of the universe may be explainable without the need for dark energy or a cosmological constant. Apparently, ripples from inflation in the early universe may account for the observed expansion rate of the universe."

Comments

But what about the Horizon problem?

[mr100percent]

But what about the Horizon problem?

From an earlier /.-linked article 13 things that do not make sense:

The horizon problem

OUR universe appears to be unfathomably uniform. Look across space from one edge of the visible universe to the other, and you'll see that the microwave background radiation filling the cosmos is at the same temperature everywhere. That may not seem surprising until you consider that the two edges are nearly 28 billion light years apart and our universe is only 14 billion years old.

Nothing can travel faster than the speed of light, so there is no way heat radiation could have travelled between the two horizons to even out the hot and cold spots created in the big bang and leave the thermal equilibrium we see now.

This "horizon problem" is a big headache for cosmologists, so big that they have come up with some pretty wild solutions. "Inflation", for example.

You can solve the horizon problem by having the universe expand ultra-fast for a time, just after the big bang, blowing up by a factor of 1050 in 10-33 seconds. But is that just wishful thinking? "Inflation would be an explanation if it occurred," says University of Cambridge astronomer Martin Rees. The trouble is that no one knows what could have made that happen.

So, in effect, inflation solves one mystery only to invoke another. A variation in the speed of light could also solve the horizon problem - but this too is impotent in the face of the question "why?" In scientific terms, the uniform temperature of the background radiation remains an anomaly.

"A variation in the speed of light could solve the problem, but this too is impotent in the face of the question 'why?'"

Also, in the same article, Dark Energy is discussed:

9 Dark energy

IT IS one of the most famous, and most embarrassing, problems in physics. In 1998, astronomers discovered that the universe is expanding at ever faster speeds. It's an effect still searching for a cause - until then, everyone thought the universe's expansion was slowing down after the big bang. "Theorists are still floundering around, looking for a sensible explanation," says cosmologist Katherine Freese of the University of Michigan, Ann Arbor. "We're all hoping that upcoming observations of supernovae, of clusters of galaxies and so on will give us more clues."

One suggestion is that some property of empty space is responsible - cosmologists call it dark energy. But all attempts to pin it down have fallen woefully short. It's also possible that Einstein's theory of general relativity may need to be tweaked when applied to the very largest scales of the universe. "The field is still wide open," Freese says.

Re:But what about the Horizon problem?

[digitalchinky]

This is all theory, but say you could instantly travel 14 billion light years to the horizon (as seen from earth)

What would you see? Another horizon a further 14 billion light years distant? My personal feeling is yes, and that the age of the universe is wrong - I don't subscribe to the big bang theory, relativity, or any other convenient explanations for this 'anomaly'. Nor do I believe in God.

I may be marked as troll, but I suspect there are many others with a similar view.

Re:But what about the Horizon problem?

[WaterBreath]

A few things:

According to "accepted" theories of expansion, there is no epicenter. All space is expanding equally in all directions. So wherever you are standing, everything will appear to expand outward away from you.

Because of that, things farther away from you will be receeding from you faster, because every extra bit of space between you and them means an extra bit of expansion, and so an extra bit of recession speed. As the theory goes, superluminal recession speeds are possible because the distant objects are not actually moving relative to the stationary frame of space in their vivinity. Space itself is changing shape, and the "motion" we see is just a side-effect.

Supposedly, there is a certain distance, which can be measured starting at any given point, beyond which every everything is receeding from the reference point faster than light, and so will never be visible from that point. This is called the Hubble distance. Related is the Hubble constant, which is a measurement of change in velocity of expansion per unit distance from the reference point. (Not the odd way to measure acceleration. Normal acceleration is m/s/s, or m/s^2, but this is m/s/m, or just 1/s, which is 1Hz. Weird, eh?) The Hubble constant is under contention, I think, and the value of the Hubble distance depends on the value of the constant.

Anyway, this stuff is kind of where the idea of Star Trek's "warp drive" comes from (at least in the more recent series). If it were possible to create some sort of device that could cause the space in front of a ship to contract and the space behind to expand proportionally, the ship could move without moving through space. It would be space itself changing shape around the ship that causes it to "move". And hence the speed at which you could move would be limited only by the speed at which you could channel energy into the expansion and contraction of space. Of course, this might just happen to be limited by the speed of light as well, so maybe superluminal speed still wouldn't be possible!

But if these guys' new idea is right, then none of that matters. =)

string theory Nova

[Fox_1]

Nova did a great piece on the all of physics (a lot on the universe and big focus on Quantum Mechanics and String Theory). It's pretty good if you are trying to find commonplace explanations of some of the theories the article just mentions and doesn't explain.

Re:Space beyond the edge of Universe

[ari_j]

Yes, there is space beyond the cosmic horizon. The horizon on Earth is just the farthest you can see because of the curvature of the planet's surface. The planet keeps going beyond the horizon - the horizon is a function of the observer. The same applies to the universe, although I am not knowledgeable enough to tell you if the cosmic horizon is the limit of what we can see because of the distance, because of a higher-dimensional curvature of the universe, or because of something else.

Gravity leaks

[Tablizer]

I've read another hypothesis recently: that gravity slowly "leaks" into other dimensions so that over long distances it's attractive force diminishes, and that is why the universe is flying apart. The average distances between the galaxies has now reached a threashold where the leakage makes a big difference, giving the appearence of a relatively sudden expansion speedup.

Re:Gravity leaks

[XanC]

Even if gravity were zero, the universe would then expand at a constant rate. But it appears to be accelerating, implying some kind of negative gravity.

What if Dark Energy Wasn't Required

[nimblebrain]

There's a decent amount of evidence that has been mounting over the past few years that a large component of redshift is in fact intrinsic, i.e. not attributed to the Doppler effect.

In some ways, it seems related to the much-glossed-over "K Effect" of a few decades ago, where it was found that bright, bright blue stars seemed to be systematically redshifted.

Researchers like M. B. Bell are of the opinion that the intrinsic redshifts are superimposed on a Big Bang flow (reducing the actual velocity we should be measuring). Others, like Arp, believe that the Hubble Flow is an illusion, and that the universe is actually relatively static once you take away the intrinsic redshifts.

David Russell's paper that just came out supports either view, and shows that other explanations (like Tully-Fisher Relationship errors or rotational velocities) are far too small to account for the large discrepancies.

(Some more hubbub on the topic.)

In either case, intrinsic redshifts will take a lot of pressure off researchers to find 'dark energy', because the discrepancies of speed/distance are much reduced.

Then, perhaps, we can stop looking for something that isn't there? :)