Could gravitational waves reveal how fast our universe is expanding?

[beecee]

https://phys.org/news/2018-07-gravitational-reveal-fast-universe.html

Since it first exploded into existence 13.8 billion years ago, the universe has been expanding, dragging along with it hundreds of billions of galaxies and stars, much like raisins in a rapidly rising dough.

Astronomers have pointed telescopes to certain stars and other cosmic sources to measure their distance from Earth and how fast they are moving away from us—two parameters that are essential to estimating the Hubble constant, a unit of measurement that describes the rate at which the universe is expanding.

But to date, the most precise efforts have landed on very different values of the Hubble constant, offering no definitive resolution to exactly how fast the universe is growing. This information, scientists believe, could shed light on the universe's origins, as well as its fate, and whether the cosmos will expand indefinitely or ultimately collapse.

Now scientists from MIT and Harvard University have proposed a more accurate and independent way to measure the Hubble constant, using gravitational waves emitted by a relatively rare system: a black hole-neutron star binary, a hugely energetic pairing of a spiraling black hole and a neutron star. As these objects circle in toward each other, they should produce space-shaking gravitational waves and a flash of light when they ultimately collide.

Read more at: https://phys.org/news/2018-07-gravitational-reveal-fast-universe.html#jCp

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the paper:

Measuring the Hubble constant with neutron star black hole mergers:

The detection of GW170817 and the identification of its host galaxy have allowed for the first standard-siren measurement of the Hubble constant, with an uncertainty of ∼ 14%. As more detections of binary neutron stars with redshift measurement are made, the uncertainty will shrink. The dominating factors will be the number of joint detections and the uncertainty on the luminosity distance of each event. Neutron star black hole mergers are also promising sources for advanced LIGO and Virgo. If the black hole spin induces precession of the orbital plane, the degeneracy between luminosity distance and the orbital inclination is broken, leading to a much better distance measurement. In addition neutron star black hole sources are observable to larger distances, owing to their higher mass. Neutron star black holes could also emit electromagnetic radiation: depending on the black hole spin and on the mass ratio, the neutron star can be tidally disrupted resulting in electromagnetic emission. We quantify the distance uncertainty for a wide range of black hole mass, spin and orientations and find that the 1-σ statistical uncertainty can be up to a factor of ∼ 10 better than for a non-spinning binary neutron star merger with the same signal-to-noise ratio. The better distance measurement, the larger gravitational-wave detectable volume, and the potentially bright electromagnetic emission, imply that spinning black hole neutron star binaries can be the optimal standard siren sources as long as their astrophysical rate is larger than O(10) Gpc−3 yr−1 , a value allowed by current astrophysical constraints.

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The above article and paper, have prompted me to ask some questions.

[1] Would our cosmological event horizon be instrumental in revealing how fast the universe is expanding? What I'm suggesting is that the closer to the cosmological EH we could monitor gravitational waves, from BH/Neutron star mergers, would our readings be more accurate?

[2] I also vaguely remember reading or hearing something about gravitational waves from the BB itself, probably if I recall correctly at about the time when LIGO was first proposed. Could we detect gravitational waves from the BB? and are there such a variety of gravitational waves? 

and [3] what if anything would/could that reveal about that quantum/Planck period of t+10-43 seconds?

[4] The speculative idea of multiverses is generally thought to be "non testable" but could gravitational waves  hypothetically be caused by and evidence for colliding universes? 

The further discoveries of  gravitational waves, and the types will by all reports open up a whole new field of cosmology and knowledge of our universe, and other questions that at this time remain more philosophical then scientific, such as us the universe finite or infinite? Was the BB simply an evolution of spacetime, or an evolution of spacetime as we currently know it, and of course the "nothing" from which our universe arose and the proper defining of what this nothing really is.

Edited July 11, 2018 by beecee

[Airbrush]

On ‎7‎/‎11‎/‎2018 at 2:19 PM, beecee said:

[4] The speculative idea of multiverses is generally thought to be "non testable" but could gravitational waves  hypothetically be caused by and evidence for colliding universes? 

Colliding big bangs? 

The word "universe" implies everything, big bang is more specific, as a region of finite size.

Other than that, very interesting post!

[beecee]

49 minutes ago, Airbrush said:

Colliding big bangs? 

The word "universe" implies everything, big bang is more specific, as a region of finite size.

Other than that, very interesting post!

Certainly with regards to the word universe, but there has been numerous, speculative ideas around now re different "bubbles"of spacetime, or multiverses, parallel universes etc. I'm just surmising that if these hypothetical universes did collide or bump into each other, could/would gravitational waves be a possible result?

[Mordred]

Think of them as different Hubble horizons as per chaotic eternal inflation.

[Eise]

On 7/11/2018 at 11:19 PM, beecee said:

Since it first exploded into existence 13.8 billion years ago, the universe has been expanding, dragging along with it hundreds of billions of galaxies and stars, much like raisins in a rapidly rising dough.

This is not from you, beecee, but from the article. In another thread this was discussed: The word 'dragging' suggests that space is a substance that can touch matter (and/or energy) and exerts a force that pushes everything around. No miracle that some people come here with wrong ideas.

I think that even popular science writers should be very careful with their words.

[beecee]

47 minutes ago, Eise said:

This is not from you, beecee, but from the article. In another thread this was discussed: The word 'dragging' suggests that space is a substance that can touch matter (and/or energy) and exerts a force that pushes everything around. No miracle that some people come here with wrong ideas.

I think that even popular science writers should be very careful with their words.

Certainly agree with those sentiments, but remember I also had to go through that period as an amateur, which is why I always enclose the paper if there is one. I have come to expect that most all journalists and their articles can be  expected to sensationalise to various extents.

Certainly what you extracted from the article and the word "dragging" does make one cringe somewhat. 

 

[Airbrush]

10 hours ago, Mordred said:

Think of them as different Hubble horizons as per chaotic eternal inflation.

Do you envision some kind of chaotic structure of big bangs occurring in isolated events or branching off of other big bangs, or both?

Edited July 13, 2018 by Airbrush

[Mordred]

There is two ways to describe a BB, the most common application is at 10^-43 seconds. However under chaotic eternal inflation you can get Hubble Bubbles that can be thought of as originating from their own BB events and treated as separate universes via causality. 

https://en.wikipedia.org/wiki/Eternal_inflation

"Eternal inflation is a hypothetical inflationary universe model, which is itself an outgrowth or extension of the Big Bang theory.

According to eternal inflation, the inflationary phase of the universe's expansion lasts forever throughout most of the universe. Because the regions expand exponentially rapidly, most of the volume of the universe at any given time is inflating. Eternal inflation, therefore, produces a hypothetically infinite multiverse, in which only an insignificant fractal volume ends inflation."

 

Myself I always preferred Higg's inflation however that is simply my opinion. Chaotic eternal is just as possible. It was originally designed to cover Runaway inflation (once inflation stops in the early treatments there was no way to turn it off.) however in modern terms this is handled through slow roll. However in science all viable theories are valid till proven invalid.

Edited July 13, 2018 by Mordred

[Airbrush]

Very interesting, I'd never heard of the Hubble Bubble.  Here is what Wiki told me:

"If...Earth were...near the center of a...low-density region of interstellar space (a relative void), denser [regions] in a shell around it would...attract material away from the center-point. Thus, stars inside such a "Hubble bubble" would accelerate away from Earth...faster than the general expansion of the universe.^[1][3] This situation would provide an alternative to dark energy in explaining the apparent accelerating universe."

https://en.wikipedia.org/wiki/Hubble_bubble_(astronomy)

I made edits to the article.  It refers to a "low-density region of interstellar space (a relative void), denser material in a shell around it would attract material away from the center-point".

Do you like the Hubble Bubble as the best current explanation for dark energy?

So possibly the vast majority of the multiverse is currently inflating?  How vast of a majority?  Our observable universe, or big bang, is among a very tiny, tiny bit of the multiverse that is not inflating?

Edited July 14, 2018 by Airbrush

[Mordred]

Its one of many theories however not one I follow, I prefer LCDM and support the evidence of DE and DM in accordance. However as mentioned until proven otherwise...