6 ms·

This is a tad disingenuous IMO. We can't "literally see the big bang happening". That's is like saying we can see the explosion of a stick of dynamite that expl

by Daho0n 6y ago

This is a tad disingenuous IMO. We can't "literally see the big bang happening". That's is like saying we can see the explosion of a stick of dynamite that exploded inside a mine because we see a dust-cloud and hear a boom a split second later at the mine entrance. We are standing outside the mine, talking about the effect of the dynamite. We see the effect (electromagnetic radiation or "the dust-wave"), not the cause or the event itself.

simonh 6y ago
I don't see how it's disingenuous, that's literally what it is. It was even predicted well in advance of measurement. If you see the flash and hear the boom, how can you credibly say that was not witnessing the event?
- Tenoke 6y ago
  The CMB is an observation well matching what you'd expect with a Big Bang but it is not the Big Bang itself and one can make other theories to try and explain it.
  - simonh 6y ago
    It's photons emitted by the plasma of the big bang, that have been propagating continuously through vaccuum since they were emitted. It's just as much seeing the big bang as the flash from an explosion is seeing it go off.
    - raattgift 6y ago
      No, in the very early universe, prior to electroweak symmetry breaking, there were no photons at all. Before that transition and up to GUT energies even closer to the Big Bang there would be SU(2) W_{1,2,3} massless particles and the U(1) B gauge boson instead. After the transition these electroweak particles combine into photons and the W and Z bosons. Wikipedia is pretty technical about this : https://en.wikipedia.org/wiki/Electroweak_interaction#Lagrangian https://en.wikipedia.org/wiki/Electroweak_interaction#Lagran... There is experimental support for the electroweak transition at the LHC at CERN and Lep. LISA (https://lisamission.org https://lisamission.org), when and if it happens, will also gather more evidence for and against the electroweak transition at cosmological scales, with somewhat less clear-cut (but still highly supportive) evidence becoming ever more available through indirect tests in the interim. The CMB photons are almost wholly from the recombination epoch at which entirely ionized atomic nuclei -- mostly single protons but other things up to Beryllium-9 -- first became electrically bound to free electrons. The neutralization of these particles releases photons. In the case of Hydrogen-1 + one electron, the emitted photon is principally at Lyman-alpha (Lya) frequencies. Because of the relative abundance of this pairing during recombination, the Lya spectral lines dominate the CMB. Redshifting preserves the (relative) structure of the Lya lines, and one result of the expanding post-recombination cosmos is that later absorbers (dust, gas) and emitters (neutral hydrogen excited by quasars and so on) produce Lya line structures that are shifted red to different degrees. The CMB is the reddest Lya structure, although it is smeared into a (differential of) a blackbody spectrum by Thompson scattering, and kinematic effects make it very nearly uniform (correcting for proper motion) in every direction. Between the end of the electroweak transition and the start of recombination, there were still many photons. These scattered off the electrically charged free electrons, nuclei, and protons, and it is extremely unlikely that there would have been a spectral structure if that light were measured because of the random lengths of photon free paths. As scattering fell off thanks to a combination of expansion (increasing the distances between charged particles) and neutralization (electrically neutral objects don't cause a relevant photon scattering) the photon mean free path became cosmologically long, terminating the randomization of the momenta of photons. Instead of being boosted up or down by process like (Inverse) Compton Scattering, photons emitted by transitions of free particles to bound systems at lower energy states remained at the emission wavelength subject to redshift from the metric expansion of space. Cosmologists work with a set of points at the time when photons that were essentially freed from scattering around the time of recombination are now reaching us, and call that the surface of last scattering. The surface of last scattering has a cosmological redshift of z ~ 1100, which places it at about 380 thousand years after the Hot Big Bang. Additionaly, we have several lines of indirect evidence for the Cosmic Neutrino Background, which was emitted more than 379 thousand years earlier than the surface of last scattering, and long-wavelength gravitational radiation detectors on constellations of spacecraft are planned that will probe gravitational waves that are even older than those relic neutrinos. Among the evidence is structural detail in the Cosmic Microwave Background that is sensitive to the density and varieties (in particular rest masses) of the extremely early Cosmic Neutrinos, because they interact both gravitationally and through chiral currents with the various early pre-electromagnetism plasmas. So the stress-energy in the cosmos was quite busy evolving well before the Cosmic Microwave Background, generating actual observables (and many reasonably-theorized observables that we just can't probe reliably today). There were several different "plasmas" between the hot big bang and the recombination era, each with very different degrees of freedom, and successively much colder temperatures. Moreover, there were lots of plasmas after the surface of last scattering, for example during "first light" as very bright UV sources reionized neutral hydrogen. I am therefore with other commenters in this thread: we don't see the big bang happening because we can't directly detect anything before the surface of last scattering, mainly because the scattering thoroughly randomized light-borne observation prior to that, secondarily because we can't detect extremely redshifted neutrinos (we have trouble enough detecting neutrinos from fission reactors we have built on Earth, or solar neutrinos, which have not been redshifted to very low energies), and tertiarily because we haven't yet built big enough networks of gravitational wave detectors. What we do see is relatively late in the pre-stellar history of the universe : it had expanded and cooled enormously by then. Analogies between the early universe and chemical or even nuclear explosions are generally pretty misleading.
      - simonh 6y ago
        I’m not saying we can see every single detail of the modern analysis of theme habits of the Big Bang directly, I’m just saying the the fact the universe started with an explosion like fireball event generating a pervasive hot plasma which cooled as the universe expanded in the far past is directly observable. That is there was a bang, it was big, and we can directly observe it.
        raattgift 6y ago
        It's inconsistent with any sort of matter explosion. First leat's deal with "there was a bang". Rather than an acoustic "bang" which has a moving sharp amplitude peak that decays back to the background as it radiates outwards, the acoustics of the hot big bang are comparable to Gaussian white noise with an almost everywhere-identical intensity that decays everywhere almost-identically (that is, the sound of the big bang is the background). The pressure waves weren't moving through anything like our atmosphere or oceans, it was simply too hot for there to be any molecules at all, and there were so many low-amplitude pressure-waves that one would have to think about trillions of trillions of trillions of simultaneous explosions and implosions, and not just one. Explosions in a medium like air or water create an overdensity (compared to some global average) shockwave that has a particular focus, not random overdensities and underdensities everywhere. Additionally, an explosion's overdensity shockwave is strongly associated with an increase in temperature -- colloquially, explosions tend to create fireballs that break up structures depending on the strength of the explosion (they can break weak molecular bonds, chemical bonds, the bonds between electrons and nuclei, and the bonds within nuclei, in increasing order of power). The hot big bang is consistent with a very hot, dense, low entropy phase suddenly expanding and cooling adiabatically everywhere, with everywhere remaining close to the average. With this expansion-driven cooling, new bonds formed, first freezing out neutrinos, quarks and gluons, baryons, hadrons, electroweak particles, weak and electromagnetic particles, and eventually less-ionized and even neutral atoms and molecular hydrogen (H2). In other words, the hot big bang's expansion produced effects in matter almost exactly opposite what one would get in an explosion. Finally, "big" in a spatial-extent sense isn't right either, as everything that is near us in our modern galaxy cluster was compacted in to something much smaller than the head of a pin. Indeed, everything we see in our sky (including at least billions of galaxies) was compacted into an area much smaller than our own galaxy.[1] Perhaps you might consider that the "big bang" was a misleading choice of name put forward on a radio broadcast in 1949, and that trying to promote it from poetic licence (or even just rhetoric) into an analogue of a chemical or nuclear explosion is futile given that Hoyle knew he was mischaracterizing (not just oversimplifying) what was known of the distant universe at the time of the broadcast. ("Big bang" is certainly fancifully poetic, and short, and those two attributes tend to be found in the jargon of theoretical physics. Consider the names of the standard model quarks, or "black hole".) - -- [1] Ethan Siegel, a theoretical astrophysicist and science writer, gives some numbers for the spatial volume of our Hubble volume as one approaches the end of the inflationary epoch (and the start of the big bang) at https://www.forbes.com/sites/startswithabang/2017/03/24/how-big-was-the-universe-at-the-moment-of-its-creation/ https://www.forbes.com/sites/startswithabang/2017/03/24/how-...
- deleted 6y ago
  [deleted]

by Daho0n 6y ago

simonh 6y ago

I don't see how it's disingenuous, that's literally what it is. It was even predicted well in advance of measurement. If you see the flash and hear the boom, how can you credibly say that was not witnessing the event?

Tenoke 6y ago
The CMB is an observation well matching what you'd expect with a Big Bang but it is not the Big Bang itself and one can make other theories to try and explain it.
- simonh 6y ago
  It's photons emitted by the plasma of the big bang, that have been propagating continuously through vaccuum since they were emitted. It's just as much seeing the big bang as the flash from an explosion is seeing it go off.
  - raattgift 6y ago
    No, in the very early universe, prior to electroweak symmetry breaking, there were no photons at all. Before that transition and up to GUT energies even closer to the Big Bang there would be SU(2) W_{1,2,3} massless particles and the U(1) B gauge boson instead. After the transition these electroweak particles combine into photons and the W and Z bosons. Wikipedia is pretty technical about this : https://en.wikipedia.org/wiki/Electroweak_interaction#Lagrangian https://en.wikipedia.org/wiki/Electroweak_interaction#Lagran... There is experimental support for the electroweak transition at the LHC at CERN and Lep. LISA (https://lisamission.org https://lisamission.org), when and if it happens, will also gather more evidence for and against the electroweak transition at cosmological scales, with somewhat less clear-cut (but still highly supportive) evidence becoming ever more available through indirect tests in the interim. The CMB photons are almost wholly from the recombination epoch at which entirely ionized atomic nuclei -- mostly single protons but other things up to Beryllium-9 -- first became electrically bound to free electrons. The neutralization of these particles releases photons. In the case of Hydrogen-1 + one electron, the emitted photon is principally at Lyman-alpha (Lya) frequencies. Because of the relative abundance of this pairing during recombination, the Lya spectral lines dominate the CMB. Redshifting preserves the (relative) structure of the Lya lines, and one result of the expanding post-recombination cosmos is that later absorbers (dust, gas) and emitters (neutral hydrogen excited by quasars and so on) produce Lya line structures that are shifted red to different degrees. The CMB is the reddest Lya structure, although it is smeared into a (differential of) a blackbody spectrum by Thompson scattering, and kinematic effects make it very nearly uniform (correcting for proper motion) in every direction. Between the end of the electroweak transition and the start of recombination, there were still many photons. These scattered off the electrically charged free electrons, nuclei, and protons, and it is extremely unlikely that there would have been a spectral structure if that light were measured because of the random lengths of photon free paths. As scattering fell off thanks to a combination of expansion (increasing the distances between charged particles) and neutralization (electrically neutral objects don't cause a relevant photon scattering) the photon mean free path became cosmologically long, terminating the randomization of the momenta of photons. Instead of being boosted up or down by process like (Inverse) Compton Scattering, photons emitted by transitions of free particles to bound systems at lower energy states remained at the emission wavelength subject to redshift from the metric expansion of space. Cosmologists work with a set of points at the time when photons that were essentially freed from scattering around the time of recombination are now reaching us, and call that the surface of last scattering. The surface of last scattering has a cosmological redshift of z ~ 1100, which places it at about 380 thousand years after the Hot Big Bang. Additionaly, we have several lines of indirect evidence for the Cosmic Neutrino Background, which was emitted more than 379 thousand years earlier than the surface of last scattering, and long-wavelength gravitational radiation detectors on constellations of spacecraft are planned that will probe gravitational waves that are even older than those relic neutrinos. Among the evidence is structural detail in the Cosmic Microwave Background that is sensitive to the density and varieties (in particular rest masses) of the extremely early Cosmic Neutrinos, because they interact both gravitationally and through chiral currents with the various early pre-electromagnetism plasmas. So the stress-energy in the cosmos was quite busy evolving well before the Cosmic Microwave Background, generating actual observables (and many reasonably-theorized observables that we just can't probe reliably today). There were several different "plasmas" between the hot big bang and the recombination era, each with very different degrees of freedom, and successively much colder temperatures. Moreover, there were lots of plasmas after the surface of last scattering, for example during "first light" as very bright UV sources reionized neutral hydrogen. I am therefore with other commenters in this thread: we don't see the big bang happening because we can't directly detect anything before the surface of last scattering, mainly because the scattering thoroughly randomized light-borne observation prior to that, secondarily because we can't detect extremely redshifted neutrinos (we have trouble enough detecting neutrinos from fission reactors we have built on Earth, or solar neutrinos, which have not been redshifted to very low energies), and tertiarily because we haven't yet built big enough networks of gravitational wave detectors. What we do see is relatively late in the pre-stellar history of the universe : it had expanded and cooled enormously by then. Analogies between the early universe and chemical or even nuclear explosions are generally pretty misleading.
    - simonh 6y ago
      I’m not saying we can see every single detail of the modern analysis of theme habits of the Big Bang directly, I’m just saying the the fact the universe started with an explosion like fireball event generating a pervasive hot plasma which cooled as the universe expanded in the far past is directly observable. That is there was a bang, it was big, and we can directly observe it.
      - raattgift 6y ago
        It's inconsistent with any sort of matter explosion. First leat's deal with "there was a bang". Rather than an acoustic "bang" which has a moving sharp amplitude peak that decays back to the background as it radiates outwards, the acoustics of the hot big bang are comparable to Gaussian white noise with an almost everywhere-identical intensity that decays everywhere almost-identically (that is, the sound of the big bang is the background). The pressure waves weren't moving through anything like our atmosphere or oceans, it was simply too hot for there to be any molecules at all, and there were so many low-amplitude pressure-waves that one would have to think about trillions of trillions of trillions of simultaneous explosions and implosions, and not just one. Explosions in a medium like air or water create an overdensity (compared to some global average) shockwave that has a particular focus, not random overdensities and underdensities everywhere. Additionally, an explosion's overdensity shockwave is strongly associated with an increase in temperature -- colloquially, explosions tend to create fireballs that break up structures depending on the strength of the explosion (they can break weak molecular bonds, chemical bonds, the bonds between electrons and nuclei, and the bonds within nuclei, in increasing order of power). The hot big bang is consistent with a very hot, dense, low entropy phase suddenly expanding and cooling adiabatically everywhere, with everywhere remaining close to the average. With this expansion-driven cooling, new bonds formed, first freezing out neutrinos, quarks and gluons, baryons, hadrons, electroweak particles, weak and electromagnetic particles, and eventually less-ionized and even neutral atoms and molecular hydrogen (H2). In other words, the hot big bang's expansion produced effects in matter almost exactly opposite what one would get in an explosion. Finally, "big" in a spatial-extent sense isn't right either, as everything that is near us in our modern galaxy cluster was compacted in to something much smaller than the head of a pin. Indeed, everything we see in our sky (including at least billions of galaxies) was compacted into an area much smaller than our own galaxy.[1] Perhaps you might consider that the "big bang" was a misleading choice of name put forward on a radio broadcast in 1949, and that trying to promote it from poetic licence (or even just rhetoric) into an analogue of a chemical or nuclear explosion is futile given that Hoyle knew he was mischaracterizing (not just oversimplifying) what was known of the distant universe at the time of the broadcast. ("Big bang" is certainly fancifully poetic, and short, and those two attributes tend to be found in the jargon of theoretical physics. Consider the names of the standard model quarks, or "black hole".) - -- [1] Ethan Siegel, a theoretical astrophysicist and science writer, gives some numbers for the spatial volume of our Hubble volume as one approaches the end of the inflationary epoch (and the start of the big bang) at https://www.forbes.com/sites/startswithabang/2017/03/24/how-big-was-the-universe-at-the-moment-of-its-creation/ https://www.forbes.com/sites/startswithabang/2017/03/24/how-...
deleted 6y ago
[deleted]