The Biggest Open Questions in Science

by Vocafy Verificato

Inglese (USA) C1 10 domande Science

Explore what scientists know about dark matter, dreams, life's origins, and other mysteries—and what remains unexplained.

1. 1. Scegli la risposta corretta.

   Which effect makes dark matter detectable indirectly?

   Stars in the outer regions of many galaxies orbit faster than the gravity of visible matter alone would predict. This is one clue that additional, unseen matter is present.

   • Its reflection of light from nearby stars.
   • Its gravitational influence on visible matter.
   • Its absorption of visible starlight.
   • Its emission of thermal radiation.

   Consider what governs a star's orbit.

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   • Its gravitational influence on visible matter.

   Unseen mass is also inferred from gravitational lensing, in which gravity bends light from background objects.

2. 2. Scegli la risposta corretta.

   What do these reports reveal about dreaming?

   People awakened during REM sleep often report vivid dreams. Dream reports also occur after awakenings from non-REM sleep.

   • Dreaming occurs exclusively during REM sleep.
   • Dreams are equally vivid in every sleep stage.
   • Dreaming is not confined to REM sleep.
   • Dreams occur only while a person is first falling asleep.

   Notice that dreams are reported after more than one kind of sleep.

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   • Dreaming is not confined to REM sleep.

   Sleep stages describe patterns of brain and body activity. Identifying when dreams occur does not, by itself, explain what dreams are for.

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   What did this experiment demonstrate?

   In a classic experiment, an electrical discharge through a mixture of gases produced amino acids—the building blocks of proteins.

   • Some building blocks of life can form without living organisms.
   • Complete living cells can emerge from gases in a single step.
   • Life must have originated in exactly that mixture of gases.
   • Amino acids can form only after living cells already exist.

   Distinguish producing useful molecules from producing a living system.

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   • Some building blocks of life can form without living organisms.

   Making amino acids is not the same as creating a system that can reproduce and evolve. That gap remains central to research on life's origins.

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   What follows from this location alone?

   An exoplanet lies in its star's habitable zone: the range of distances where a suitable atmosphere could allow liquid water on the surface.

   • The planet must already have a stable ocean.
   • The planet must have an atmosphere like Earth's.
   • The planet must support organisms that depend on water.
   • Surface liquid water is possible, but not guaranteed.

   The definition includes a condition about the atmosphere.

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   • Surface liquid water is possible, but not guaranteed.

   An atmosphere can strongly affect surface temperature. A promising orbit therefore does not establish that a planet is habitable, much less inhabited.

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   Ignoring the loss of sunlight, what would happen to Earth's orbit?

   In a thought experiment, the Sun is replaced by a black hole with exactly the same mass. Earth remains at its present distance, far outside the black hole's event horizon.

   • Earth would inevitably spiral into the black hole.
   • Earth's orbit would remain essentially unchanged.
   • Earth would escape because only luminous objects can hold planets in orbit.
   • Earth would orbit much faster simply because the replacement is smaller.

   The central object's mass and Earth's distance have not changed.

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   • Earth's orbit would remain essentially unchanged.

   At this distance, the gravitational pull depends on mass, not on whether the central object shines. Black holes are not cosmic vacuum cleaners.

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   What is conserved in this process?

   An electron and its antiparticle, a positron, can annihilate and produce two photons. The photons have no rest mass, but they carry energy.

   • The total rest mass of the particles.
   • The number of electrons and positrons.
   • The separate electric charges of the original particles.
   • The total energy, including the energy associated with mass.

   The original particles disappear, but the photons carry something away.

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   • The total energy, including the energy associated with mass.

   Annihilation does not mean energy disappears. Why the early universe left a surplus of matter over antimatter is a separate, unresolved question.

7. 7. Scegli la risposta corretta.

   What is accelerating in this discovery?

   Observations of distant supernovae helped reveal that cosmic expansion is accelerating. In the standard cosmological model, dark energy accounts for this acceleration, but its physical nature remains unknown.

   • The expansion of space on large scales.
   • The orbital motion of every star within its galaxy.
   • The rotation of all galaxies around a single cosmic center.
   • The expansion of individual atoms as the universe grows.

   Think about distances between faraway galaxies, rather than changes within objects.

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   • The expansion of space on large scales.

   Gravity can keep galaxies and solar systems bound even while distances between widely separated galaxies grow.

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   What distinction does this phenomenon reveal?

   Some people with damage to the brain's main visual area can guess an object's direction of motion better than chance, despite reporting that they see nothing in that part of their visual field.

   • Conscious vision is fully preserved whenever a person guesses accurately.
   • Visual information cannot affect behavior without awareness.
   • Processing visual information and consciously seeing are not identical.
   • Damage to the brain's visual areas prevents every response to light.

   Compare what the person can do with what they report experiencing.

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   • Processing visual information and consciously seeing are not identical.

   Known as blindsight, this phenomenon helps researchers separate visual processing from reported awareness—a useful distinction in studying consciousness.

9. 9. Scegli la risposta corretta.

   What prevents this from becoming a faster-than-light messaging system?

   Distant observers can measure entangled particles and discover correlations when they compare their records. Each observer's individual measurement outcomes are random.

   • The correlations vanish beyond a fixed separation distance.
   • Neither observer can choose a local outcome to encode a message.
   • Every measurement sends an ordinary light signal to the other particle.
   • The particles must be brought back together before either can be measured.

   Sending a message requires control over the information being transmitted.

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   • Neither observer can choose a local outcome to encode a message.

   The observers must compare their records through an ordinary communication channel to identify the correlations. Entanglement does not provide controllable instant communication.

10. 10. Scegli la risposta corretta.

    What is the most careful interpretation of the predicted infinity?

    When standard cosmological models based on general relativity are traced far enough backward, they predict an initial state of infinite density. No observation has directly measured such a state, and quantum effects are expected to matter at these extremes.

    • The mathematical prediction alone establishes that a physical infinity existed.
    • General relativity must be unreliable in every setting.
    • Quantum effects can safely be excluded from the earliest cosmic history.
    • The model may be reaching the limits of its physical usefulness.

    A successful theory need not remain complete under conditions far beyond its tests.

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    • The model may be reaching the limits of its physical usefulness.

    A theory can work extremely well in tested conditions and still reach its limits at extremes. This is one reason physicists seek a quantum theory of gravity.