We are in the room indicated by the janitor.<\/p>\n\n\n\n
The four enter the room. It\u2019s a small waiting area with a closed door at the back. Papaia knocks on the door. After a few seconds, a nurse appears, wearing a mask and gloves.<\/p>\n\n\n\n
Nurse: Good morning. How can I help you?<\/p>\n\n\n\n
The four look visibly embarrassed.<\/p>\n\n\n\n
Papaia (whispering.): The boss sent us here to take \u201cthe\u201d test.<\/p>\n\n\n\n
Nurse: Ah! I see. No need to be embarrassed. It happens to everyone at some point.<\/p>\n\n\n\n
Banani: Really?<\/p>\n\n\n\n
Nurse: Of course! Don\u2019t worry. By the way, let me check your names in the registry\u2026 Hmm, that\u2019s strange! I can\u2019t find you.<\/p>\n\n\n\n
Papaia: What now?<\/p>\n\n\n\n
Nurse: Normally, I wouldn\u2019t be able to let you take the test without registration, but since it\u2019s the boss who sent you, I\u2019ll make an exception.<\/p>\n\n\n\n
Papaia: Oh, thank you!<\/p>\n\n\n\n
Nurse: If you pass me your ID cards I\u2019ll add your names to the registry.<\/p>\n\n\n\n
The four hand over their ID cards to the nurse, who writes their names into the registry.<\/p>\n\n\n\n
Nurse: All right, before we start, can you please tell me what symptoms you\u2019re experiencing?<\/p>\n\n\n\n
Ravioli (embarrassed): Excuse me, but I thought there\u2019d be a bit more \u2026 privacy for this kind of thing.<\/p>\n\n\n\n
Nurse: Ah, yes, I see! Of course, you\u2019re right! You can enter my office one at a time. Who wants to go first?<\/p>\n\n\n\n
None of the four get up from their chairs.<\/p>\n\n\n\n
Nurse (pointing at Ravioli): Then you go first!<\/p>\n\n\n\n
Ravioli: Me?<\/p>\n\n\n\n
Ravioli reluctantly gets up and enters the room with the nurse.<\/p>\n\n\n\n
Banani: I\u2019ve never seen such an unusual psychologist before!<\/p>\n\n\n\n
Papaia: I agree. The gloves and mask? And the privacy of the session\u2026 doesn\u2019t seem optional to me!<\/p>\n\n\n\n
Banani (curious): Speaking of masks\u2026 Hey Papaia, I\u2019m starting to have a doubt.<\/p>\n\n\n\n
Papaia: What doubt?<\/p>\n\n\n\n
Banani: You see, earlier, the janitor scolded us for not wearing masks. And now the psychologist is also wearing one.<\/p>\n\n\n\n
Papaia: So what? Where are you going with this?<\/p>\n\n\n\n
Banani: \u2026 Could it be that our problem is really\u2026 contagious?<\/p>\n\n\n\n
Igor: Oh, yes! Banani\u2019s \u201cproblem\u201d is indeed \u2026 contagious! And it seems like I\u2019m the only one here immune\u2026 to his stupidity!<\/p>\n\n\n\n
While Papaia and Banani wait for Ravioli, who is taking \u201cthe\u201d test, they seize the opportunity to continue their conversation about Hubble tension.<\/p>\n\n\n\n
Banani: Are you sure, Papaia, that you measured Hubble\u2019s constant correctly?<\/p>\n\n\n\n
Papaia: I\u2019m 100% sure! We repeated the measurements many times in every possible way. You were there too, don\u2019t you remember?<\/p>\n\n\n\n
Banani: Yes, but in the end, what\u2019s the problem if we get two slightly different values?<\/p>\n\n\n\n
Papaia: You see, Banani, we measured the same constant in two different ways. The first with redshift, the second with the CMB background radiation. If this constant is truly constant, the values should be very close to each other.<\/p>\n\n\n\n
Banani: I still don\u2019t get it.<\/p>\n\n\n\n
Papaia: Let me give you an example. Imagine measuring Earth\u2019s gravitational acceleration, which we call \u201cg.\u201d<\/p>\n\n\n\n
Banani: You mean the force that keeps us grounded and makes everything fall to the ground?<\/p>\n\n\n\n
Papaia: More or less\u2026 \u201cg\u201d represents the value of the acceleration caused by that force.<\/p>\n\n\n\n
Banani: Pretty much the same thing, right?<\/p>\n\n\n\n
Papaia: Not exactly: to calculate the force, we also need mass to do the calculation: mass times acceleration. But in this case, we\u2019re just measuring the acceleration \u201cg.\u201d<\/p>\n\n\n\n
Banani: I think I get it.<\/p>\n\n\n\n
Papaia: And the value of \u201cg\u201d on Earth\u2019s surface is constant, meaning it doesn\u2019t change over time, and it\u2019s about 9.81 meters per second squared.<\/p>\n\n\n\n
Banani: Yeah, I think I\u2019ve heard that number before, maybe at school.<\/p>\n\n\n\n
Papaia: Essentially, when anything is in free fall, its speed increases by about 9.81 meters per second every second.<\/p>\n\n\n\n
Banani: I think I\u2019m following you.<\/p>\n\n\n\n
Papaia: Great! So, we can measure this value in various ways. For example, using the oscillations of a pendulum or a ball rolling down an inclined plane. These are two independent methods to measure the same thing, \u201cg.\u201d<\/p>\n\n\n\n
Banani: I see. We\u2019re using two measurement methods to measure the same quantity.<\/p>\n\n\n\n
Papaia: Very good, I see you\u2019re getting it now. So, both with the pendulum and the inclined plane, we should, and do, always get the same result: 9.81 meters per second squared.<\/p>\n\n\n\n
Banani: But that\u2019s not what happens with Hubble\u2019s constant?<\/p>\n\n\n\n
Papaia: Exactly! That\u2019s the issue. When we measure Hubble\u2019s constant with redshift, we get 67.4 km\/s\/Mpc (kilometers per second per megaparsec). But when we measure it with the CMB, we get 73 km\/s\/Mpc.<\/p>\n\n\n\n
Banani: But those are different values!<\/p>\n\n\n\n
Papaia: Exactly, and we have an error greater than 8%!<\/p>\n\n\n\n
Banani: Couldn\u2019t it be the instruments, as the boss says?<\/p>\n\n\n\n
Papaia: No, Banani! Let me explain. According to the theoretical model, we expect a value of 67.5 km\/s\/Mpc. This value is perfectly confirmed by the most advanced spectroscopes, which have a maximum error margin of 1%. But when we measure the same constant with the CMB method, using advanced instruments like the Hubble and Webb space telescopes, we get a value of 73 km\/s\/Mpc, despite their 1% error margin.<\/p>\n\n\n\n
Banani: Surely 8 percent is off the charts!<\/p>\n\n\n\n
Papaia: That\u2019s why something doesn\u2019t add up in the Big Bang model.<\/p>\n\n\n\n
Igor: I agree, the Big Bang doesn\u2019t add up! Just like this situation doesn\u2019t add up. In fact, we have found a nurse\u2026 as a psychologist!<\/p>\n\n\n\n