startswithabang: The biggest problem for the expanding Universe might be trouble for dark energy&ldq
startswithabang: The biggest problem for the expanding Universe might be trouble for dark energy“According to the CMB, the rate that the Universe is expanding today (the Hubble rate of expansion) is 67±1 km/s/Mpc, while according to the other (distance ladder) method, that rate is 74±2 km/s/Mpc. This might not seem like such a big deal, as you might say to yourself, “maybe it’s somewhere between the two values: 70 looks about right.” But these uncertainties are now so small that the two possible measurement values do not overlap. Instead, we’re left with only two possibilities:1.) There’s a fundamental flaw in one of the methods used: perhaps the assumptions and inferences of the CMB are incorrect, or perhaps our inability to calibrate the smaller distances on the distance latter are skewing us away from the true values.2.) Or, more excitingly, perhaps both measurements are correct and they’re measuring different things, implying that some major component of the Universe, like dark matter or dark energy, is changing over time.”The Universe could have had any number of fates, even given that it started out with a hot Big Bang. Gravitation could have overcome the initial expansion, eventually causing a recollapse and a big crunch. The expansion could have been too great, and caused a runaway expansion that always slowed but never ceased. Yet the Universe gave us a surprising option that was none of the above: acceleration due to dark energy. It’s our measurements of astrophysical objects at great distances and the fluctuations of the cosmic microwave background that allowed us to determine our expansion history. Yet those two sources, when we look at them in detail, give results that conflict with one another! Does this mean that one of the measurements is problematic? Or, perhaps more excitingly, does that mean dark matter or dark energy is changing over time? -- source link
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