I Can the big rip ever be ruled out?

  • I
  • Thread starter Thread starter Trollfaz
  • Start date Start date
  • Tags Tags
    Big rip Rip
AI Thread Summary
The discussion centers on the conditions necessary for the Big Rip to occur, specifically the requirement that the dark energy equation of state parameter w must be more negative than -1. Current observations suggest w is close to -1, but there is insufficient evidence to definitively rule out the Big Rip scenario. While experiments can push the potential onset of the Big Rip further into the future, they cannot eliminate the possibility entirely. Concerns about dark energy density violating energy conservation laws are addressed, noting that general relativity complicates the conservation of energy concept. Ultimately, without a definitive value for w or a breakthrough in quantum gravity theories, the Big Rip remains a possibility.
Trollfaz
Messages
143
Reaction score
14
In order for the big rip to happen, the dark energy equation of state w must be more negative than -1, allowing dark energy density to grow.
https://en.m.wikipedia.org/wiki/Big_Rip
According to Wikipedia, the current observed w value is very close to -1 but it acknowledges that there is insufficient evidence to strictly disprove the big rip
I read Katie Macks book called The End of Everything and inside it, she mentioned that all experiments have an error therefore we cannot force the value of w to be exactly -1. So we can push the big rips earliest date further into the future but not indefinitely far. So far the latest data assures that there will be no rips for the next 200 billion years according to the book.
But doesn't increasing dark energy density violate the law of energy conservation. There is no mechanism we know of that allows this.
 
Space news on Phys.org
The actual value of ##w## might be greater than -1, in which case we might eventually exclude all ##w\leq-1## models. If the actual value of ##w## is exactly -1 then you are correct that we could not rule out the Big Rip from measurement of ##w## alone. Other discoveries could rule it out, of course. For example a working theory of quantum gravity might allow us to derive ##w## from more fundamental considerations.
Trollfaz said:
But doesn't increasing dark energy density violate the law of energy conservation. There is no mechanism we know of that allows this.
Conservation of energy is a complicated topic in general relativity. In the global sense that you are using it here, there's no way to state it - and since we can't state it no scenario violates it. And in the local sense where a conservation law can be stated quintessence doesn't violate it.

It's worth noting that there are ways of "kind of" stating a global energy conservation law in GR. Some physicists are convinced by these and some aren't - I don't know where your book stands on the topic. I don't understand the subject well enough to comment on whether the Big Rip violates any of these kinda-sorta-laws, but there are enough serious physicists who don't accept them at all that I'd say worrying about possible violations of global energy conservation is putting the cart before the horse. We need to agree (a) that there is such a law, and (b) what it is before we worry about whether a scenario violates it.
 
As @Ibix has mentioned, if w is exactly -1 then experimental error will never allow you to rule out ##w < -1## (except by statistical errors - either systematic or random). This is true for any measured quantity with a particular value. Take the photon mass for example. It is zero in our models because that works very very well. However, experiments cannot rule out a teeny tiny mass ##< 10^{-18}## eV (pdg.lbl.gov).
 
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
The formal paper is here. The Rutgers University news has published a story about an image being closely examined at their New Brunswick campus. Here is an excerpt: Computer modeling of the gravitational lens by Keeton and Eid showed that the four visible foreground galaxies causing the gravitational bending couldn’t explain the details of the five-image pattern. Only with the addition of a large, invisible mass, in this case, a dark matter halo, could the model match the observations...
Hi, I’m pretty new to cosmology and I’m trying to get my head around the Big Bang and the potential infinite extent of the universe as a whole. There’s lots of misleading info out there but this forum and a few others have helped me and I just wanted to check I have the right idea. The Big Bang was the creation of space and time. At this instant t=0 space was infinite in size but the scale factor was zero. I’m picturing it (hopefully correctly) like an excel spreadsheet with infinite...
Back
Top