Leave these fields empty (spam trap):
Name
You can leave this blank to post anonymously, or you can create a Tripcode by using the format Name#Password
Comment
[i]Italic Text[/i]
[b]Bold Text[/b]
[spoiler]Spoiler Text[/spoiler]
>Highlight/Quote Text
[pre]Preformatted & Monospace Text[/pre]
[super]Superset Text[/super]
[sub]Subset Text[/sub]
1. Numbered lists become ordered lists
* Bulleted lists become unordered lists
File

Sandwich


420chan is Getting Overhauled - Changelog/Bug Report/Request Thread (Updated July 26)

Study finds possible alternative explanation for dark energy

Reply
- Tue, 30 Dec 2014 19:38:01 EST ksAXy5yQ No.54870
File: 1419986281805.jpg -(19458B / 19.00KB, 305x244) Thumbnail displayed, click image for full size. Study finds possible alternative explanation for dark energy
http://phys.org/news/2014-12-alternative-explanation-dark-energy.html
>The predicted effects of time being faster in the past would have the effect of making the plot of supernovas become linear at all distances, which would imply that there is no acceleration in the expansion of the universe. In this scenario there would be no necessity to invoke the existence of dark energy.

So pretty much if this is true, Dark Energy doesn't exist and it's observed effects are really caused by time dilation. Hubble expansion is really just an illusion caused by time slowing as the universe ages. We see acceleration at increased distances because when you look farther away it means you look back in time, and time is actually slowing down.

Also, this would imply that as the state of the acceleration is essentially linear, there will be no Big Rip or Big Crunch because the acceleration is not positive or negative. The universe will likely end in a slow Heat Death.
>>
Anders Angstrom - Wed, 31 Dec 2014 05:59:14 EST 0PqgsQ8H No.54871 Reply
Well that would be a pretty huge deal. Neat.
Couldn't it just be photons slowing down? If the speed of light is slowing somehow wouldn't that result in the exact same observation?
>>
Annie Cannon - Wed, 31 Dec 2014 07:30:47 EST w9Ju60EU No.54872 Reply
Fuck yeah, I love it. Just finished reading the paper (http://news.uga.edu/documents/Kipreospone0115550.pdf), though I skipped the math and I'm sure a lot of the depth are lost on me, but there's still a lot of accessible detail not included in the press release.

To summarize: Special Relativity doesn't account for movement in a gravitational field, gravitational centers create preferred reference frames, which affects the way we see the universe, taking this into account means the universe is older and bigger than we thought, cosmic expansion isn't accelerating, and dark energy is probably going the be the new aether.

I feel like this should be a party thread. I nominate it for best science of 2014.

>>54871
The speed of light is a dimensioned quantity, and the effects of it changing range from nothing at all (if other dimensioned quantities change in proportion so that dimensionless quantities remain constant) to contradicting everything we see and know. Perhaps there's a scenario in there somewhere which corresponds to Absolute Simultaneity Theory, but without further factors to indicate which combination of parameters change and and how, talking about the speed of light changing by itself is meaningless.

BTW, this reminded me of Wetterich's cosmology: http://www.nature.com/news/cosmologist-claims-universe-may-not-be-expanding-1.13379. I wonder what effect Kipreos's theory will have on Wetterich's.
>>
Otto Struve - Wed, 31 Dec 2014 09:26:22 EST 415JX8nG No.54873 Reply
I actually thought about this a while ago.
If the universe was denser in the past, wouldn't time go by faster?


Does this also mean it may be possible to define the cosmological constant?
>>
Viktor Ambartsumian - Wed, 31 Dec 2014 17:25:21 EST 7d1GyK7j No.54874 Reply
This is not a big deal, there are dozens of alternative models. It's really not hard to explain the supernovae data with an alternative model. Being able to explain this single data set doesn't prove much, a local bias in H0 can do it. Fitting the BAO peak would be more impressive.

I should point out this isn't a better model, it's just another one with even less handwavey justification compared to say a cosmological constant.

>Hubble expansion is really just an illusion caused by time slowing as the universe ages.
No, the article makes it clear he still has an expanding universe. To explain away that there is a great deal more evidence. Hubble expansion is just linear expansion.

>Also, this would imply that as the state of the acceleration is essentially linear, there will be no Big Rip or Big Crunch because the acceleration is not positive or negative.
Without a cosmological constant you will have deceleration. It's not clear what the model implies, physorg is a terrible news site.
>>
Viktor Ambartsumian - Wed, 31 Dec 2014 17:47:35 EST 7d1GyK7j No.54875 Reply
>>54872
>Special Relativity doesn't account for movement in a gravitational field
Special relativity doesn't account for gravity at all, this was literally the motivation for general relativity. If this is what he's arguing I don't buy it, i will read it later.

There are papers like this every month which make grand claims based on a single test. Newsflash, you can build a model to fit data. If you take them all at their word you will be faced with a new cosmology every month.
>>
Viktor Ambartsumian - Wed, 31 Dec 2014 18:46:36 EST 7d1GyK7j No.54876 Reply
1420069596908.png -(58646B / 57.27KB, 402x596) Thumbnail displayed, click image for full size.
>>54875
The bottom line of the paper is pretty simple, it doesn't explain away dark energy and probably it won't fit other cosmological tests.

>Note that while the UTD scenario provides an alternate view of the recent increased effects of dark energy, it does not address the mechanistic basis for linear Hubble expansion, which may involve the cosmological constant/
dark energy.

Ah, a model which doesn't remove any parameters. How fantastically redundant. This is a model that claims to explain dark energy but assumes an underlying cosmology it cannot explain.

>it should be noted that GRC theories have substantial inherent flexibilities that allow the theories to model diverse observations

As opposed to this one model which explains one dataset. This model will not fit BAO, to fit the supernovae it has to alter z and M, in BAO there is no M, it is just position and redshift. One other things that bugged me.

>The prevailing theory, while it can accurately model the effects of dark energy, is mechanistically not understood at multiple levels,
including the nature of dark energy, and why it has significantly increased activity only in the most recent era.

Wrong. Lambda only dominates late time because the matter density has dropped. That's not something someone proposing a cosmological model should get wrong.
>>
Giovanni Cassini - Wed, 31 Dec 2014 20:50:17 EST ksAXy5yQ No.54877 Reply
>>54874
My bad, a semantic error on my part made me confuse "hubble expansion" with "accelerating expansion".

That's really not what I meant to say at all.
>>
Fritz Zwicky - Wed, 31 Dec 2014 21:01:27 EST XwQwdExC No.54879 Reply
Since the earth (along with the rest of the galaxy) is moving through intergalactic space at nearly 2 million miles per hour, does that mean our galaxy has its own unique amount of time dilation (with respect to other galaxies/celestial structures? Does time run slower in faster-moving galaxies? I mean, does it make a difference whether a galaxy is moving towards/away from your point of reference? For example, could the degree of time dilation in one galaxy appear to be higher when observed from one galaxy, but appear to be lower when observed from another galaxy that is moving in a different direction from the first? If our solar system existed in a different galaxy moving a different direction, would the time on that bizarro-earth run at a different "clock" compared to our Milky-Way Earth?
Does that even make sense? Sorry, time dilation confuses me...

Also, how does light even propagate at all, when anything traveling that fast would have so much time dilation that its time for it would've slowed to basically a complete halt? How can it appear to move at 299,792,458 meters per second when it takes it an infinite amount of years for it to even "experience" one second?
>>
Galileo Galilei - Wed, 31 Dec 2014 21:35:01 EST 7d1GyK7j No.54880 Reply
>>54879
>Since the earth (along with the rest of the galaxy) is moving through intergalactic space at nearly 2 million miles per hour, does that mean our galaxy has its own unique amount of time dilation (with respect to other galaxies/celestial structures?
Yes there is time dilation (as long as is not expansion due to the expanding universe). Both galaxies will see the other running slow, that is one of the cornerstones of relativity. Neither is more right than the other in this observation.

>I mean, does it make a difference whether a galaxy is moving towards/away from your point of reference?
It does. This is the Doppler effect, slightly different from time dilation. If something is moving towards you you observe them sped up because the distance the light has to travel from them to you decreases every second so if you were watching a clock tick you would see it run fast. If it was running away it would be slow. This is just like hearing the pitch of an ambulance siren change as it passes you. The important thing about relativity is that the even if it is running perpendicular to the line of sight (getting neither closer nor farther away) there is an observed slowing, this is time dilation.

>For example, could the degree of time dilation in one galaxy appear to be higher when observed from one galaxy, but appear to be lower when observed from another galaxy that is moving in a different direction from the first? If our solar system existed in a different galaxy moving a different direction, would the time on that bizarro-earth run at a different "clock" compared to our Milky-Way Earth?
Yes but the important thing is that time dilation due to velocity is symmetric, they see your clock tick slow, you see their clock tick slow. Different galaxies would see different degrees of time dilation if they had different velocities.

>Also, how does light even propagate at all, when anything traveling that fast would have so much time dilation that its time for it would've slowed to basically a complete halt?
Some people would claim the photon experiences no time, it can propagate because that is not time dilated. However strictly special relativity does not describe time dilation for light. Relativity assumes just two things but one of them is that light is away measured at the same speed in all frames. To calculate time dilation for an object you need a frame traveling alongside the object, not allowed for light.

>>54873
Possibly, possibly not. The universe is either flat or just closed. If it is flat then then there would be no time dilation because the global geometry would be unchanged. Either way it would be very minor accept in the very early universe.

You can already measure fit a value for the cosmological constant, OmegaLambda is about 0.7. However a cosmological constant is just the simplest model of dark energy, it doesn't have to be correct.
>>
James Elliott - Thu, 01 Jan 2015 20:38:37 EST XwQwdExC No.54883 Reply
1420162717080.gif -(703718B / 687.22KB, 256x256) Thumbnail displayed, click image for full size.
>>54880
very interesting, thanks for your reply. I find time dilation really fascinating.

About "gravitational time dilation":
What if gravitation was merely a secondary effect of increased time dilation (rather than the other way around, i.e. time dilation being "caused" by increased gravity), with objects having a natural tendency to gravitate towards regions of spacetime with slower time? Do you think this is at all possible?

Even a spaceship traveling at a significant fraction of the speed of light would have greatly increased mass (according to E=mc^2), and therefore would also have a greatly increased gravitational field. In this case, the increased gravity would act like natural "drag" to slow the velocity of the spacecraft down to a more neutral speed (with respect to other moving bodies in the universe). Is it at all plausible to consider that gravity may be a "fictitious force" like we consider the centripetal force to be?

sorry if these are dumb questions
>>
Giovanni Cassini - Fri, 02 Jan 2015 08:47:54 EST ksAXy5yQ No.54887 Reply
>>54883
If anything, things would seem to move away faster as they move into space that experiences a faster time rate. Oh wait, they already do and this is why we think there's dark energy.

All this still doesn't explain dark matter.
>>
Henry Russell - Sun, 04 Jan 2015 14:25:15 EST ksAXy5yQ No.54890 Reply
>>54887
Thought experiment, feel free to dismiss this as nonsense.

What if dark matter is somehow linked to the apparent mass increase objects experience as they approach light speed?

In localized areas where the time is not moving faster, objects to not seem to have any increased mass. But more distant objects, which are relatively moving faster and faster away from us approaching light speed more and more, objects are actually apparently gaining mass due to general relativity.

This could be tested by measuring the mass of extremely distant objects over time but I'm afraid it would take too much time, in human years, to observe a change.

Report Post
Reason
Note
Please be descriptive with report notes,
this helps staff resolve issues quicker.