Search results for query: *

Yes agreed a cyclic universe by definition repeats. Can we also agree that a cyclic universe is not the only model where the universe is infinitely old ? Can we also agree that there are many different types of cyclic universe so if you are going to critique one you need to specify which one it...

Which cyclic model are you talking about? Ekpyrotic? CCC? VSl? Baum Frampton? Higgs Bang? There are many cyclic models so one should not talk of cyclic model generically. Moreover one does not even need to assume a cyclic universe to assume an infinitely old universe. Many models of quantum...

It depends on how you define big bang. If you define big bang as an evolution from a hot dense state then an infinitely old universe could easily have a big bang. In many cosmological models there are is a period of contraction prior to a period of expansion. This sort of evolution still has a...

The universe is not necesarily static prior to infation, here is one possibility: http://arxiv.org/abs/1302.0254

A simulation in a computer is not the same as doing an experiment or collecting data from nature. You can't do that with the constants of nature.

Just one thing to add the LWC bounce does not replace inflation Just one thing to add, there are bounce models that replace inflation but I think most papers in LQC assume inflation happens after the bounce. An interesting result in LQC is the claim that the supposed fine tuning of inflation...

Thanks Marcus.

Nor sure if this has already been discussed. But recently Rovelli has suggested the mysterious Fast Radio Bursts might be from Planck Stars : https://www.gravity.physik.fau.de/events/tux3/rovelli.pdf Any thoughts? What are the other explanation and how can resolve this?

So in that case, it seems to me that if we see a red tilted primordial gravity wave spectrum with no large devaition from gausianity then we can start handing out Nobel prizes for inflation, but not before? Do you agree?

Thanks for that Bapowell. Is this something that alternatives to inflation such as Ekpyrosis, VSL, CCC, string gas cosmology etc can explain as well or is it unique to inflation?

Al lot of the answers to your questions depends on how you define terms like "universe" and "big bang". these terms can have varying definitions and so you can get different answers depending upon which definition you use. Question: Was the universe a tiny ball? Firstly let's look at the word...

I think there is some confusion between chaotic inflation and eternal inflation. Even some big name comsologists like George Ellis seem to make this mistake. Eternal inflation leads to a multiverse, chaotic inflation is eternal inflation, but eternal inflation is not necessarily chaotic...

The model you are referring to ( colliding branes) is the Ekpyrotic model of Turok and Steinhardt. You can read abut it here: http://en.wikipedia.org/wiki/Ekpyrotic_universe In cosmology when people talk about a multiverse they are normally talking about eternal inflation which is a very...

Thanks, thought so.

Very interesting as always Marcus, that's pretty impressive they get a scale invariant spectrum wihtout an inflaton field, but what about the problems that inflaiton is supposed to solve? monopole, horizon etc?

What i think most cosmologists agree with is that one needs a quantum thoeyr of gravity to understand what happened at the big bang. Does anyone here disagree with that? Attempts to apply existing candidate theories for quantum gravity such as strings, loop and Horava gravity all seem to point...

Very interesting , thanks for posting Marcus. hope I will get time to watch that soon. I get the impression there are in some sense two classes of bounce models. Those that try and replace inflation and solve the puzzles of cosmology by introducing a pre big bang era that then bounces. Then...

We have made a third film in our "Before the Big Bang" series for youtube. Our first centred around an interview with Abhay Ashtekar and focused on LQC Our second Sir Roger Pernose on CCC This fetaures an interview with Gabrielle Veneziano (founder of string theory), Ali Nayeri ( who works...

Some loop people have been estimating the number of e folds at around 145: http://arxiv.org/abs/1301.1264

Mdoern bouncing comsolgies are not necessarily cylic models. They basically change the Friedman equation at veyr high curvature regimes only . We know that the unvierse was in such a regime 13.8 bio years ago and so there may have been a bounce then. If the universe exapnds forever ,as is the...

Nothing in science is ever 100% proved. we can get to levels of evidence that are overwhelming and silly to doubt but that's not quite the same thing Two short articles on singularities I think you should read: http://www.einstein-online.info/spotlights/big_bangs...

Thanks for that JEdishufu, I see the mention of DECIGO in the document but again nothing to justify a 2027 launch as per the wikipedia page. i really hope its true though, but somehow I doubt it.

Thansk for that, didnt see it mention DECIGO but nice document . its just great ot hear there is international support for but has any money actualy been put on the table for it? Do we have any reason to believe a 2027 launch date?

I just noticed that the wikipedia page of DECIGO: http://en.wikipedia.org/wiki/Deci-hertz_Interferometer_Gravitational_wave_Observatory says its due to launch in 2027. Does that it mean it has any funding? i thought it was a just a proposal at the moment, am I wrong?

Heres a new one proposed by Turok and Stenihardt ( of Ekpyrotic fame): http://arxiv.org/abs/1307.8106 string gas cosmology is another, pre big bang string duality is another. There are probably many more. MOnd is more trying to explain dark matter without dark matter , its nto as far as I know...

For what its worth I was at a conference in Oxford to discuss CCC. The presentation by Gurzadyan was not well recived as Bapowell has pointed out. However another study by a Polish team did seem to be go down better with the critics. I'm not saying they accepted it either but here is the link...

First off Bicep 2 results look like they are increasingly ocming into doubt: https://www.physicsforums.com/showthread.php?t=753482 even if the results do hold up there still needs to be further investigation to see if it confirms inflation or not. As Bapowell said nothing in science is proved...

Thank you for that Modred , this look slike the same energy scale as inflation is supposed to happen. So i preumse its at the same time, is that right? Also given you say its model dependant what are the range of estimates with regards to inflaiton. do some models say before inflationa and...

As i understand it, at some point in the early unvierse, the Higgs field was off, then it swtiched on. Is this correct? I can't find when this is supposed to have happened, does anyone know?

An interesting blog post arguing the reason that BICEp 2 and PLAnck are in tension is becuase BICEP 2 underestimated galactic foreground emission. http://resonaances.blogspot.co.uk/2014/05/is-bicep-wrong.html

Im not saying it should be.

Whether or not Penrose criticisms of string theory, Qm and inflation are good criticisms have nothing to do with his own ideas of consciousness. Even if the latter ideas are total nonsense it does not make his criticisms any less valid. I think the phrases "fashion/faith/fantasy" are obvious...

I thought MArcus and Bapowell might be interested in this paper: http://arxiv.org/abs/1403.7623 a claim bounce prior to inflation is a better fit than just inflation. Anyone like to comment? i presume a lot of people will be trying to fit their favourite models to this data even before its...

Doesnt this argument require that we can predict whether or not life arises given a set of physical laws and constants of nature? I have to doubt this assumption. if i gave you the standard model of particle physics and the values for all the constants would you predict that our universe has...

Ive often seen "matter bounce" suggested as an alternative to inflation. However in standrad LQc you go form bounce to super inflation to inflation and so on. So in this standard scenario, is it different to the phrase "matter bounce" are there different types of bounces?

http://blankonthemap.blogspot.co.uk/2014/03/b-modes-rumours-and-inflation.html

Thanks and can this be done from the ground or does it need a space based mission?

Hi Bapowell, I missed your post sorry. But thanks, your paper was very interesting. Can I confirm that given the results today it is still the case that current data cannot tell us the tilt of the spectrum and only a future space mission will do be bale to do so? Planck polarisation data should...

Thanks MArcus , can't wait to get a chance to watch the video. Sorry to keep bugging, but what about the issue of red tilt versus blue tilt in the primordial gravity wave spectrum? Can that/has that been addressed by BICEP 2 data or not?

Here are the results: http://bicepkeck.org/ for a news story see here: http://www.nature.com/news/b-mode-1.14884 A lot of stories running this as proof of inflation if confirmed. However as I understood it discovering the b Mode was not enough, we need to know if the gravity wave spectrum is red...

An interesting paper claiming that the detection of the B mode is not enough to rule in favour of inflation but the tilt of the spectral slope needs to be red, others models give a blue tilt but still detectable gravity waves: http://arxiv.org/pdf/1104.3581.pdf What will it take to measure...

re Monday pres conference. The day after Andei Linde one of the fathers of inflationary theory is giving a talk athe joint MIT/Tufts seminar. I don't think this was on their schedule previously . The title of the talk is "Inflation News and Persepective. The poster is below and has no other...

One blog is saying Alan Guth and Andrei Linde are rumoured to be at the press conference, didnt mention a source for this http://cosmobruce.wordpress.com/2014/03/14/108/ the blog also doubts the "detection" will have a sufficiently high sigma.

A prior paper from BICEP giving a preview here: https://www.cfa.harvard.edu/~cbischoff/bischoff_iaus288.pdf [Broken]

Theres also the possibility of testing different models of the early early universe (maybe even before inflation ) with B modes, for example: http://iopscience.iop.org/1742-6596/484/1/012060/pdf/1742-6596_484_1_012060.pdf But again I presume this requires a space based mission, please correct me...

So I am guessing theyv'e found evidence for the b mode polarisation of the CMb. If so , how much can we learn from a ground based detector? Do we need a space based project like CORE, PRISM or EPIC?

Primordial gravity waves news story doing the rounds Gravitational waves: have US scientists heard echoes of the big bang? http://www.theguardian.com/science/2014/mar/14/gravitational-waves-big-bang-universe-bicep

http://map.gsfc.nasa.gov/news/7yr_release.html "The 7-year data provide compelling evidence that the large-scale fluctuations are slightly more intense than the small-scale ones, a subtle prediction of many inflation models."

If you read Alan Guths account of the history of inflation, it was invented to solve one problem and one problem only: the mono pole problem. It was only realized afterwards that it then solves the flatness and horizon problems and gives an explanation to the origin of structure. That to me is...

Thanks again Marcus, this is really fascinating stuff. Ill come over to that forum, the reasons i think it has comso implication is because if this signal is found then it gives quite a boost to the big bounce idea, don't they use the same modified Freidman equation? Anyway see you over at the...