Meta & Fysikken: Afsnit 93: Supernovaer! Hvorfor er de så interessante?
Idag taler vi om Karina’s eget specialområde. Anders er lidt langsom i opstarten, men kommer hen ad vejen så nogenlunde med!
Og så taler vi om tilfældigheder. Hvordan definerer vi egentlig - ud fra et videnskabeligt synspunkt - tilfældigheder? Og hvordan har tilfældigheder indflydelse på forskningen? Kan man tage højde for dem?
Her er Karina’s noter til dagens afsnit:
1: SN1987A, endelig er neutronstjernen blevet fundet.
Min PhD var om denne supernova. Derfor meget stor nyhed i mine øjne.
2: Nova-Eksplosioner (ikke supernova).
https://videnskab.dk/rummet/sker-hvert-80-aar-se-nova-eksplosion-med-det-blotte-oeje/
Dette sker inden September i år og kan ses med en normal kikkert.
Billedet er fra: https://en.wikipedia.org/wiki/T_Coronae_Borealis
3: Universets udviddelse: JWST og Hubble Space Telescope er enige.
The Hubble tension is quite probably the biggest problem deviling cosmology, and it has to do with the rate at which the Universe's expansion is accelerating – a fundamental measurement of the Universe. We have several methods of deriving this, but the two main ones are standard candles and standard rulers.
*Standard candles are lights in the dark with known intrinsic brightness. That's Cepheid variable stars and Type Ia supernovae. If we know how intrinsically bright something is, we can calculate how far away it is, with high precision. Cepheid variable stars and Type Ia supernovae give us a Hubble constant of around 73 kilometers per second per megaparsec.
*Standard rulers are based on signals from the early Universe. These include the cosmic microwave background – the light that first streamed through the Universe about 380,000 years after the Big Bang – and baryon acoustic oscillations, both of which give us a Hubble constant of around 67 km/s/megaparsec.
Current cosmological models work very well in some respects, so proposed solutions generally mean that something else gets broken. Human error, therefore, becomes an attractive explanation for the Hubble tension, so scientists keep measuring, re-measuring, and measuring again, looking for the place where we stuffed up.
One possibility is that we did something wrong with the original Hubble measurements, so Riess and his colleagues have been using JWST to check their work. Initial measurements made last year were consistent with the Hubble observations; but there was a possibility that, the deeper into space we peered, the more the two sets of measurements could diverge, with the Hubble Cepheid distance measurements becoming less accurate with distance.
Well, now JWST has caught up to Hubble, and that's just not the case. The measurements are all consistent.
"We've now spanned the whole range of what Hubble observed, and we can rule out a measurement error as the cause of the Hubble Tension with very high confidence," Riess says. "Combining Webb and Hubble gives us the best of both worlds. We find that the Hubble measurements remain reliable as we climb farther along the cosmic distance ladder."
4: Randomness
Hvad er Random?
Wall of Entropy - En væg med lava lamper
Background Randomness:
In common usage, randomness is the apparent or actual lack of definite pattern or predictability in information.[1][2] A random sequence of events, symbols or steps often has no order and does not follow an intelligible pattern or combination. Individual random events are, by definition, unpredictable, but if there is a known probability distribution, the frequency of different outcomes over repeated events (or "trials") is predictable.[note 1] For example, when throwing two dice, the outcome of any particular roll is unpredictable, but a sum of 7 will tend to occur twice as often as 4. In this view, randomness is not haphazardness; it is a measure of uncertainty of an outcome. Randomness applies to concepts of chance, probability, and information entropy.