1) Forums : Cosmology and Astronomy : 'Serious gap' in cosmic expansion rate hints at new physics (Message 21679)
Posted 24 Apr 2018 by Profile Benjamin Wandelt
Hi -

This is directly related to what we are doing here - PICO, which we developed using your computations on C@H, is heavily used to derive the Planck/CMB constraints. The recent challenges have been used to validate the results, increasing our confidence in the Planck/CMB results.

As the referenced BBC article describes, there is a tension between the measurement of the expansion speed of nearby objects vs the expansion speed inferred when using the observed patterns in the ancient Cosmic Microwave Background, that reaches us from the furthest observable parts of the universe.
This could mean that the universe changed its expansion speed recently, which would woudl be an exciting discovery.
Unfortunately it is possible that the issue is just that one of the two data sets are wrong; and the results from the recent universe have historically not been as stable as the conclusions drawn from the distant universe. This is perhaps not what you expected, since the nearby universe ought to be easier to study... the problem is that it's more complex and therefore harder to interpret.

At this point we need additional data to arbitrate between the two possibilities of exciting new fundamental physics, and just one of the data sets being interpreted incorrectly.

Watch this space!
2) Forums : General Topics : Why do you participate in Cosmology@Home? Who is the \"most surprising\" participant? (Message 21470)
Posted 13 Jun 2017 by Profile Benjamin Wandelt
Great, thank you for your support.
I hope we won't disappoint!

All the best,
3) Forums : Cosmology and Astronomy : Dark Energy Demo Room (Message 21236)
Posted 15 Dec 2016 by Profile Benjamin Wandelt
Hi Jeffrey -

Remember to click inside the game before pressing S to start - it doesn't register the key stroke otherwise and nothing happens.

All the best,
4) Forums : Cosmology and Astronomy : Is the speed of light constant? (Message 21232)
Posted 13 Dec 2016 by Profile Benjamin Wandelt
Thanks for your post. Yes this is relevant to cosmology. At this point the best measurement of the claimed very precise prediction by the varying speed of light hypothesis is consistent with the world's best constraints coming from the Planck data analysis.
I am personally a bit sceptic regarding the claimed uniqueness of this prediction given that we know so little about the detailed physics at this epoch. If it is true the ever precise measurements coming from the Cosmic Microwave Background polarization and other probes will eventually be able to distinguish this model from other approaches that predict a range of possible values. If you're interested to know how this works (even if the data agrees with both models) ask me and I will tell you about relative model probabilities in Bayesian stats...

Till then,
All the best,
5) Forums : General Topics : Any status info? (Message 21138)
Posted 29 Jul 2016 by Profile Benjamin Wandelt
Hi Misho -

Thanks for your post!

For general background you could peruse the cosmic background pages on my home page at the University of Illinois. That material is still valid even if it has not been updated for a while.

Several more recent updates have been posted directly on the forum as well - check out the News section.

If you questions about the science, please do not hesitate to post in the Cosmology and Astronomy section of the forums, which we check periodically.

6) Forums : Wish list : Badges (Message 21066)
Posted 16 May 2016 by Profile Benjamin Wandelt
Hi again -

Any thoughts on any of the points in my previous post?

7) Forums : Wish list : Badges (Message 21063)
Posted 11 May 2016 by Profile Benjamin Wandelt
Hi all -

Very interesting idea. Just as a spontaneous thought - can we crowd source this?

As my contribution here is a list of ideas for badge names - loosely orderd from the nearby and more familiar to the more exotic or distant.

Neutron Star
Black Hole
Star cluster
Dwarf galaxy
Galaxy Cluster
Dark Matter
Dark Energy
Gravitational Lensing
Cosmic Microwave Background Temperature
Cosmic Microwave Background Polarization
Big Bang
The Universe

Yes, I know I'm mixing a lot of things, from elementary particles to astronomical observables, but they are all important for cosmology (even the moon, for example some important constraints on gravity come from precision lunar ranging), so why not? There are of course many other things I could have put on, but I've limited the list to things/concepts that we know exist or must be there in some form or another. I also did not include theories etc... or names of famous cosmologists...

So if we took this as given, maybe some of the more graphically talented amongst you can have a go at submitting artwork (watch the format, there seems to be a conventional size for the badges etc... but I'm not the expert on that, so please ask the others writing in this thread.)


Edit: removed the second "Baryons"
8) Forums : Cosmology and Astronomy : How many black holes are there? (Message 20746)
Posted 23 Jan 2016 by Profile Benjamin Wandelt
Hi Peter -
This is a question that touches on current research themes... in other words we don't know the answer very precisely at this time. It's only been in the last year or two that cosmological simulations have had the ability to resove individual galaxies and include mechanisms for the formation of black holes (so-called sub-grid models, see below). Examples are the Horizon-AGN simulation run that was performed by my colleagues here at the Institut d'Astrophysique de Paris (one of the first such runs). Another is the EAGLE run done by a consortium of other groups. The links are worth checking out for impressive visualizations and movies of the simulation results.

The difficulty with these runs is that the detailed physics of black-hole formation works on much shorter time-scales and length scales than can be resolved in these large simulation volumes even with the largest current supercomputers.

For this reason the formation of black holes is not simulated from first principles but using prescriptions (called "sub-grid models") that compute the probability of black hole forming in a particular grid cell, and then randomly add a black hole based on this probability. The details of the black hole (ie the accretion disk physics etc) are also not simulated but the winds from the accretion disk etc are computed based on the density, temperature etc of the cell that contains the black hole).

As a result the number of black holes at any given time depend on the parameters of the sub-grid models. The approach is to run a few simulations with different plausible values of these parameters and then to compare the results with observations of the real universe.

So to answer your question: yes there are cosmological simulations that compute the fraction of total mass in gas, stars, black holes and even the abundances of various chemical elements etc. But the results do not just depend on fundamental laws of physics but on approximate "recipes" and particular choices of the parameters of these recipes. The results are difficult to validate since this is really frontier research.

For now comparison to deep astronomical observations are our best bet at validating the sub-grid models.

Hope this helps!

9) Forums : Cosmology and Astronomy : Dark Energy Demo Room (Message 20563)
Posted 6 Nov 2015 by Profile Benjamin Wandelt
Thanks Julie -
I hope you enjoyed the free mini-games. Let me know if you have any questions!
10) Forums : Wish list : OSX (Message 20291)
Posted 26 Aug 2015 by Profile Benjamin Wandelt
Hi, cosmology@home enthusiasts who are OSX users!

I'm happy to announce that the new cosmology at home server (currently in beta release here) supports OSX!

As you've noticed there's been a bout of recent activities and new developments, signs of more to come.

Let me take this opportunity to thank Marius, Kevin, and Mark who are driving these changes.

All the best,
11) Forums : General Topics : Appeal to Project Managers (Message 20249)
Posted 3 Jul 2015 by Profile Benjamin Wandelt
Hi -
Thank you for your message.

I agree that we have been lacking in our communication activities.

The good news is that we are taking active steps to improve the project at the moment. We have been using the small amount of funding we have on keeping C@H up. We had some downtime yesterday due to a hardware failure. This has now been resolved.

We are now working on a major upgrade of C@H this summer. This will involve
- migration of c@h to a new, more stable, and more robust server,
- upgrade to the latest BOINC version,
- some infrastructure changes that will allow us to push new code versions much more efficiently.

These changes will set us up for launching new cosmology applications (beyond the current CAMB).

More updates to follow.

Let me thank you for your patience and for your continued involvement in C@H.

Best regards,
12) Forums : Cosmology and Astronomy : Dark Energy Demo Room (Message 20237)
Posted 29 May 2015 by Profile Benjamin Wandelt
Hi all,

I am not sure I ever advertised this: a while ago I started putting together some interactive web apps to illustrate concepts related to the expansion of the Universe and dark energy. The first couple of interactive demos are up, so have a look!

One app is called "Expansion" and shows some surprising features of the cosmic expansion; in particular, how the universe can expand without a unique center!

The other is a simple game called "SuperNova Hunter" which illustrates some aspects of observing the universe to get a handle on the physical properties of dark energy. When you play it a few times you'll find yourself adopting a similar strategy to that used by actual astronomer who hunt supernovas (supernovae for those who had Latin at school) to learn about dark energy.

Have ideas for other expansion/dark energy concepts that could be illustrated with interactive apps? Post your responses here!

Thank you!

Best regards,

13) Forums : General Topics : Project News Updates (Message 13102)
Posted 25 Jun 2013 by Profile Benjamin Wandelt
Hi all

Many thanks for interest and your patience!

I just wanted to take a few minutes to thank you for your effort on behalf of cosmology@home. We have made great strides in the last years and I am very pleased to see that our servers held up in the recent Dutch Power Cow stampede!

An update from us on the progress we are making with cosmology@home is overdue. The first Planck analysis has been released and I am glad to report that Pico (the code that we are feeding and training with the results from cosmology@home) was used extensively during the cosmological parameter analysis. We have readied a major update for the website (including new hardware).

I just heard that the hardware has arrived and if there are no unforeseen problems it should come online later this week. Then we will deploy the website upgrades.

I will post more next week about the changes, also in other threads, but you've heard it here first.

Oh, and Go Dutch Power Cows!

And of course, thank you to all our other faithful supporters throughout the years!

All the best,
14) Forums : Cosmology and Astronomy : Featured Concept: Dark Matter (Message 11523)
Posted 31 Jul 2012 by Profile Benjamin Wandelt
Ok, so let me expand a bit on my comment in an earlier post "...a real chance of being resolved in the near future..." since it's now gone beyond just an insider rumor and there are a couple of more detailed science papers about it.

First in plain English: there is a real chance that a tell-tale signature of dark matter has now been observed.

Now in sciencese: a couple of analyses now see a line feature in the energy spectrum of gamma rays observed by FERMI satellite at an energy of around 129 GeV.

Why is this exciting? A line feature is exactly what would be expected if a massive particle annihilates and the release energy is liberated in gamma rays.

There are astrophysical sources of gamma rays as well, but they tend to be much more broad band, since the can produce gamma rays of a range of energies.

However, if two dark matter particles, each of mass 129 Gev moving at "normal" speeds (ie not close to the speed of light) run into each other then would decay at leastinto two other particles each carrying away 129 GeV of energy, and for symmetry reasons there would be no more and no less of that amount, leading to a well defined energy of the gamma rays. Counting up gamma rays detected by the Fermi satellite in bins of energy then leads to a big pile showing up in the 129 GeV bin - hence a line.

There are some who consider such a line signal a smoking gun of dark matter. And we may now have seen it.

One of the interesting properties of this line is that it is seen towards the galactic center (where there is a lot of dark matter but not away from the galaxy where we would not expect to see it if it were indeed dark matter. Also, the signal persists when the anaysis is re-done masking known astrophysical sources of gamma rays, just to exclude that some unknown mechanism, however unlikely, could produce such a line signal without dark particle decays being involved.

We had on of the authors of the first paper that found this line, Thorsten Brinkmann, at IAP a couple of months ago and we were all trying to pick apart his argument. In the end I thought it was pretty convincing.

Of course, it didn't take long for people to notice that this energy of 129 GeV was basically the same as the mass of the Higgs boson that was announced even more recently. Of course there are already model builders who are trying to explain this coïncidence.

Exciting times!

All the best,

15) Forums : Technical Support : Tasks will not complete (Message 11416)
Posted 14 Jul 2012 by Profile Benjamin Wandelt
Thank you - that makes sense. There weren't very many points where checkpointing was easy without a lot of additional coding. If you want to share your machine between different projects, it seems the best way to do that for now is to run cosmology@home exclusivelyfor a while and then switch over to the other projects.

But we'll keep this in mind for future versions of the kernel.

16) Forums : General Topics : Word Link at C@H (Message 11415)
Posted 14 Jul 2012 by Profile Benjamin Wandelt
17) Forums : Technical Support : Tasks will not complete (Message 11410)
Posted 13 Jul 2012 by Profile Benjamin Wandelt
The code controling the progress bar is on the least tested parts of our BOINC instrumentation, so it is quite posaible for that to have a bug which makes progress appear to jump backwards at various points (essentially right after checkpoints). This may explain some of this behavior.
Also, some work units compute cosmology in open or closed universes which makes them take a lot longer than the ones where the universe is exactly flat. To simplify allocation of credit we decided to award a constant amount of credit for all work packages. This credit amount is somewhat high on purpose to make up for these special work units.

Thank you for highlighting this problem again. We will look at it in our pending update to the new kernel.

Best regards,
18) Forums : Technical Support : Problems running project!! (Message 11189)
Posted 2 Jun 2012 by Profile Benjamin Wandelt
Hi Peter -

Welcome to Cosmology@Home!

The work units do take a long time to complete. There are occasionally download errors and uploading sometimes takes several attempts.

In spite of this, the code recovers from this, eventually finds a work unit to download and does work.

We will continue to hunt for these bugs until we've found them but for now we hope that you can be patient with us!


19) Forums : Technical Support : URGENT PROBLEMS THREAD (2009 and after) (Message 11039)
Posted 7 May 2012 by Profile Benjamin Wandelt
Any news on this? Did the download errors become less frequent or---dare I say it---disappear?

20) Forums : General Topics : Error while editing User-Profile (Message 11026)
Posted 5 May 2012 by Profile Benjamin Wandelt
Yes we finally fixed it - please see this message on the announcement message board. Please help spread the good news.


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