# Tag Info

50

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 ...

41

You surely know that string theory has zillions of vacua. Most of these vacua can immediately be ruled out e.g. because they have the wrong number of macroscopic dimensions, or for similar reasons. But among those that remain possibilities - possessing the right qualitative possibilities - it is exceedingly difficult to calculate anything testable. The ...

29

Have you perhaps mistaken the meaning of the word "law" in this context? It simply means "pattern" or "regularity". If a given property or behaviour is neither constant nor varying in some regular way, then it would not be a regularity so it would not be a law. Some parts of the universe are very different from others. E.g. In ...

28

As an experimental physicist I will answer the title. The examples of inconsistency in the question deal with many assumptions on cosmological observations and models, and are answered by @MitchellPorter. If string theory is inconsistent with observations, why hasn't it been rejected yet? The standard model of particle physics is an encapsulation of all ...

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, ...

21

The big bang model$^{1}$ is an attempt to explain a host of observations that tell us how the universe evolved from its first fraction of a second onwards. It started off by being grounded in fundamental and rather well understood physics (General Relativity, particle physics and nuclear physics at relatively low energies). The model itself has evolved and ...

19

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 ...

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:/...

17

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 ...

16

Within the Standard model of particle physics, the most general experimentally verified model of fundamental physics (excluding gravity), there are quantum fields, such as the electron-positron field, that are truly fundamental. Other fundamental fields within the Standard model include the tau, muon, muon- tau- and electron-neutrino fields, quark fields, ...

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 !

13

The hypothesis that the fundamental laws of physics are the same everywhere in the universe and at all times is based on empirical evidence. Detailed observations of distant galaxies confirm that physical constants such as the fine-structure constant, the cosmological constant, the proton to electron mass ratio and the speed of light in vacuum have remained ...

13

It is unlikely that we can detect gravitational waves from the Big Bang with current technology. Due to universal expansion, such waves would have very large wavelengths. We would need interferometers that are thousands, perhaps millions, of kilometers long to detect them. The LIGO observatory simply would not be sufficient. To put things into perspective, ...

11

String theory's apparent "incompatibility" with the existence of de Sitter vacua and inflation is just a sharpening of the apparent "incompatibility" of quantum field theory, semi-classical quantum gravity and holography with de Sitter cosmological solutions and inflation. There is a strong tension between de Sitter cosmologies and ...

11

Does the Earth really go around the Sun, or is this just a mathematical convenience? For some purposes we use a geocentric model and say "the sun rises in the East"; but creating a geocentric model which accurately reproduces all observations would be hideously difficult, and rather pointless, since the heliocentric model exists, gives accurate ...

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 ...

10

Quantum fields can exchange energy. So for example when an electron and a positron annihilate the energy that was in the electron/positron field is transferred to the photon field. The result is that one electron and one positron disappear and two photons are created. The fields themselves are still both present - only the energy in the fields has changed. ...

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 ...

9

Let's consider an example of this violation. Consider the electrostatic attraction strength (Coulomb's constant). If we compute it and get some value $k_1$ in our labs, we might conclude that it is a law of nature that $F=k q_1 q_2 /r^2$. If we look at another part of the universe we might find some $k_2 \neq k_1$. Is this a violation? One might say that ...

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

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 ...

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 ...

8

As this question opens up a great deal of discussion, I would also like to pitch in. I am not saying that the answers already given by @anna v and @Mitchell Porter are not good and solid answers, I would like to add something very quickly. Even if -and that is a huge if- string theory in its current formulation is proved to be inconsistent with the data it ...

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

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.

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