# Tag Info

49

The actual paper (pdf) is very heavy in error quantification - and rightly so. They presented an experiment result that is statistically extremely difficult to obtain. But for the rest of us, conclusion is the most important part. The abstract says: The observed B-mode power spectrum is well fit by a lensed-$\lambda$CDM + tensor theoretical model with ...

24

With the proper definition of the "size" of the universe, this question does make sense. The standard model of cosmology would say that the universe is infinite which therefore does not have a "size". However, if we take into account that the big bang occurred $13.7 \pm 0.17$ billion years ago we can define a meaningful size for the observable universe. You ...

21

This is a common point of confusion, not only with regards to inflation, but any time an expanding universe comes up... The "cosmic speed limit" as you call it says that no particle or signal can move through spacetime faster than the speed of light. Spacetime is a very specifically defined thing, described with a coordinate system. There is no restriction, ...

18

They announced that through observation of the Cosmic Microwave Background, via the BICEP2 experiment in Antarctica, particularly the polarization on a 2-4 degree angular scale, gravitational waves from inflation during the early universe are being indirectly observed. Link to FAQs about the release: http://bicepkeck.org/faq.html Link to pre-print: http:/...

16

So I've done some further research into this question and the result I found is quite surprising. There truly is no set definition. Some cosmologists will tell you (as John Rennie mentioned) to avoid using the term "Big Bang" unless you absolutely have to. However, that is a luxury not afforded to all cosmologists. The more surprising thing is that among ...

15

The Big Bang was originally defined as the zero time limit of the FLRW metric, so it's a mathematical construct and not primarily something physical. We have chosen to apply it to the zero time limit of the universe because we thought the FLRW metric was a good description of the universe, but then inflation gatecrashed the party and spoiled the fun. So if ...

15

The answer is no. And to be clear about this: the set of quantum fields in their least energy state, which we call the vacuum, when left to its own devices, in the absence of stuff (including gravitating stuff) does not fluctuate at all. In this context the term 'fluctuation' was introduced by well-meaning physicists in an attempt to draw an analogy ...

14

The matter-antimatter asymmetry requires the three Sakharov conditions to be satisfied. I'll summarise that link's explanation. Unfortunately, your question isn't completely solved. The first condition is that some interactions don't conserve baryon number (I.e. baryons minus antibaryons, baryons being three-quark hadrons such as protons and neutrons). How ...

13

"The Damhsa Theory proposes that these oscillations are actually gravitational waves from the continued ramifications of the expanding universe and that ice ages and inter-glacials such as our current Holocene are a result of theses waves" That really got accepted at a Nasa conference on Solar Radiation and Climate ? In short - no !

10

As @Rennie states, no-one knows what the inflaton is. The current state of affairs is that it is generally accepted that a period of exponential expansion took place during the early universe. This explains many of the features of the observable universe that are otherwise extremely hard to explain. One of the big industries in cosmology is to try to build a ...

10

The metric expansion of space is a fundamentally different phenomenon than the relative motion of two objects in the flat spacetime of Special Relativity: While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, it places no theoretical constraint on changes to the scale of ...

10

Your question is not specific to inflation, and really applies to any case where a bosonic quantum field behaves semiclassically due to macroscopically large occupation numbers. One very simple example of this is the Stark effect in quantum mechanics, where a Hyrodgen atom is placed in a uniform electric field. The atom is treated as a quantum mechanical ...

9

First, there is no reason why all possible higher-order terms of the Einstein-Hilbert action could not in principle be there. At low energies, the effects of these higher-order terms would be less relevant, and to describe all of our astrophysical observations (on which General Relativity is based) we might suffice using only a the terms of lowest order in ...

8

Actually, that first statement is not correct. The universe isn't expanding due to dark energy. It's accelerating due to dark energy. The normal expansion, called metric expansion, is an effect of general relativity. When you get a homogeneous distribution of matter or radiation(a perfect fluid, a uniform gas, radiation, a homogeneous distribution of ...

8

Dr. Matt Strassler has some great info on his site, see here: http://profmattstrassler.com/2014/03/17/a-primer-on-todays-events/ http://profmattstrassler.com/2014/03/17/bicep2-new-evidence-of-cosmic-inflation/ http://profmattstrassler.com/2014/03/18/if-its-holds-up-what-might-bicep2s-discovery-mean/ Here's a summary of some key points in my own words (any ...

8

Light always travels at the speed of light when in a vacuum. Space is a pretty good vacuum. So if it's been travelling for 13.7 billion years, then it has travelled 13.7 billion light years. There is no contradiction here. Yes, those galaxies are now 46 billion light years light years away, but this is because the universe has expanded. You can find lots ...

8

The most straightforward theories of inflation assume there exists some scalar field $\phi$ that permeates the Universe and drives inflation. Over time this scalar field changes, and the rate of change is given by $\dot{\phi}$. There is also some "potential energy" associated with the scalar field, which is given by some function $V(\phi)$. The specific ...

7

The short answer to this question is that we do not know. The subject of your question is still in early "speculative", theorizing, and researching stages. I can say this because collisions of bubble universes under the eternal inflation theory just happens to be my specific area of work. Non-colliding bubble universes (and the local potential minima in the ...

7

Righteo, I'm basically copying this out of Weinberg Chapter 2. Apologies for copying, but I'm not sure there is really anything of substance that I could add. (I believe this qualifies as fair use as it is an insubstantial portion of the entire work and is being used for educational purposes. Any errors are my own typos.) The number density of photons in ...

7

Because space itself was expanding faster than the speed of light. Which is perfectly acceptable by the way with Special Relativity, because the speed of light is only a barrier for matter traveling through space. There is no such limit for the speed with which space itself can expand (or contract), as far as I know.

7

I could start this answer by saying that space isn't really the thing that's expanding; that it's the scale factor of the metric that's growing larger. But I won't because that's just an overcomplicated way of saying space is expanding. But to answer your question, the most correct way to think about it would be that the grid points are getting farther apart....

7

As mentioned, this is not the first evidence for gravitational waves. The data from BICEP2 shows that there is a much higher amount of B-mode polarization than what is predicted by gravitational lensing alone. According to theory, this could only be due to higher amplitude tensor modes in the CMB than previously observed (or rather, lack of observed). These ...

7

The time used in describing the evolution of the universe is comoving time. This is the time that would be measured by a freely moving observer on their wristwatch (assuming the high temperatures didn't melt both the observer and the wristwatch :-). Time is not a simple thing to define in general relativity, however we can always unambiguously define proper ...

7

Linde's model, unlike the first model proposed by Guth, assumes random initial conditions. So Chaotic = almost arbitrary initial conditions This implies that not all regions of space will undergo inflation. However the patches that do no inflate will become insignificant, while the other will dominate due to the exponential increase in volume. In fact ...

7

OK, I found a recent link: Planck versus BICEP2 Despite the new data, the collaboration did not give any insights into the recent controversy surrounding the possible detection of primordial "B-mode" polarization of the CMB by astronomers working on the BICEP2 telescope. If verified, the BICEP2 observation would be "smoking-gun" evidence for the rapid "...

7

During inflation you have the inflaton field which stays almost constant in a flat region of its potential and therefore drives the exponential expansion of the universe. Because the universe expands by a huge amount during inflation ($\sim e^{60}$) the energy density of any particles that there might have been is diluted and therefore, for all intents and ...

6

The cosmological constant has an interesting history behind it. Originally, when Einstein introduced his theory of general relativity in the early 20th century, the Einstein Field Equation, which was the equation for the gravitational field, described gravity as the effect of the curvature of space-time due to the presence of matter and energy. Perhaps you ...

6

Gravitational waves have never been directly detected. Gravitational waves are predicted by general relativity and have been inferred from other observations. Strong evidence of gravitational waves is the change in period of the Hulse-Talyor binary star system. Energy is being lost from the system at a rate consistent with radiation of gravitational ...

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