Author Topic: Astronomy/cosmology questions...  (Read 17662 times)

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Offline Rusty Edge

Re: Astronomy/cosmology questions...
« Reply #255 on: November 16, 2018, 05:51:16 AM »
Okay, here's a new one for me- DARK FLOW
I was following some links and found myself here-  https://www.newscientist.com/article/mg20327246.000-13-more-things-dark-flow/

Could you illuminate the subject for me?

Offline Geo

Re: Astronomy/cosmology questions...
« Reply #256 on: November 16, 2018, 12:08:51 PM »
Sure! :link:

Offline E_T

Re: Astronomy/cosmology questions...
« Reply #257 on: November 17, 2018, 02:40:03 AM »
Just watched something about the (relatively) recent discovery of the "super" Crater in Northern Greenland.  Some of the hypothesis have the impact around sometime during the last major Ice-age and that the ice sheet was likely much thicker at the time.

Granted, we do have a fairly good understanding of impact energies when hitting water as well as dry land (so as to create a crater of x size).  But what about when Ice is involved, when you take into account the latent heat quotient of not just one phase change (water to vapor) but also the second phase change (ice to water) for all that Ice.

How much would that change (or muddy up if you will) the calculations of the probable size and energy of the impacting object?

And, there have been questions about ejectra from the impact (or lack there of, but most could be currently under existing ice - some conjectures about side glance hit, but still), would the rapid melt/vaporization have any possible effect of how that might get distributed?
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Offline Geo

Re: Astronomy/cosmology questions...
« Reply #258 on: November 18, 2018, 05:27:30 PM »
And, there have been questions about ejectra from the impact (or lack there of, but most could be currently under existing ice - some conjectures about side glance hit, but still), would the rapid melt/vaporization have any possible effect of how that might get distributed?

IIRC (the article mentioned it I think), the courtyard meteor which gave the researchers the idea of looking for impact signs in this location is a part of the ejecta.

Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #259 on: November 19, 2018, 06:49:32 PM »
How much would that change (or muddy up if you will) the calculations of the probable size and energy of the impacting object?

Quite a bit, it would appear. The estimate given for energy/mass/speed of the impactor is based purely on the size of the crater. But if you dig into the paper, the authors acknowledge:

Quote
If ice was present and its thickness was comparable to the impactor’s diameter, then a more energetic projectile is required to produce a crater of the observed size, and the fraction of non-ice debris in the ejecta would be smaller than if the impact hit ice-free land (19).

And 19 is a reference to another paper modeling crater formation in icy layers on Mars. The abstract says:

Quote
The presence of an icy layer significantly modifies the cratering mechanics. Observable features demonstrated by the modeling include variations in crater morphometry (depth and rim height) and icy infill of the crater floor during the late stages of crater formation. In addition, an icy layer modifies the velocities, angles, and volumes of ejecta, leading to deviations of ejecta blanket thickness from the predicted power law. The dramatic changes in crater excavation are a result of both the shock impedance and the strength mismatch between layers of icy and rocky materials.

So... given that the crater they found looks pretty standard and they didn't see ejecta in the nearby ice, I'm leaning toward there not having been ice at the time. /me shrugs.

Offline ColdWizard

Re: Astronomy/cosmology questions...
« Reply #260 on: December 06, 2018, 05:34:35 PM »
If dark matter and dark energy are negative mass fluid and the fluid is continuously created, where does it come from?

Offline Geo

Re: Astronomy/cosmology questions...
« Reply #261 on: December 06, 2018, 11:00:10 PM »
If dark matter and dark energy are negative mass fluid and the fluid is continuously created, where does it come from?

Black holes!

Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #262 on: December 07, 2018, 02:13:14 PM »
Here's my go to wet blanket physicist on the negative mass fluid thing:

http://backreaction.blogspot.com/2018/12/no-negative-masses-have-not.html

She is not exactly complimentary. On the "where does it come from" question, she says:

Quote
Farnes also introduces a creation term for the negative masses so he gets something akin dark energy. A creation term is basically a magic fix by which you can explain everything and anything. Once you have that, you can either go and postulate an equation of motion that is consistent with the constant creation (or whatever else you want), or you don’t, in which case you just violate energy conservation. Either way, it doesn’t explain anything. And if you are okay with introducing fancy fluids with uncommon equations of motion you may as well stick with dark energy and dark matter.

Offline Geo

Re: Astronomy/cosmology questions...
« Reply #263 on: December 07, 2018, 05:13:56 PM »
Every theory has to start at square one.

Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #264 on: December 07, 2018, 07:51:23 PM »
Right, but we're not at square one here. As she points out in her post, she and many other experts in GR have played with the idea of negative mass/energy before. The theories haven't gained much traction because problems arise when you try to reconcile them with general relativity. This guy hasn't really addressed those previously explicated problems, so there's not a great reason to take his theory seriously.

Offline Geo

Re: Astronomy/cosmology questions...
« Reply #265 on: December 07, 2018, 10:18:05 PM »
Oh, I don't take this theory seriously at all.
The negative repellant thing sounded to good to be true. One of my thoughts was that it could allow a sort of hyperspace travel.
Hence my black hole comment a couple posts ago, since they so to speak suck matter in.

 

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