Do other universes exist? Three different ideas and their tests
Space beyond the horizon, eternal inflation and Everettian branches mean different things. Explore their assumptions, possible tests and the boundary between a model and a discovery.
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#cosmology
Articles: 12
How might the history of the Universe end?
Heat death, the Big Rip and the Big Crunch: which assumptions lead to each scenario and why precise future dates depend on the model.
Does the Universe have a centre or an edge?
The centre of expansion, the centre of our observable region and cosmic horizons are different concepts. Why a limit on observations is not a wall around the Universe.
What is dark energy?
How supernovae and cosmic scales reveal accelerated expansion, what negative pressure means, and what the new DESI results have not yet proved.
What is dark matter?
Galaxy rotation, lensing and cosmic structures point to additional mass. Follow those lines of evidence and distinguish them from the search for unknown particles.
How did the first atoms form?
Why light nuclei and neutral atoms appeared in different epochs: primordial nucleosynthesis, hot plasma, gradual recombination and light escaping.
What happened in the universe's first seconds?
Quark–gluon plasma, cooling and reaction freeze-out: how particle physics reconstructs the first seconds, and where that reconstruction has limits.
What does the Big Bang mean?
A hot, dense cosmic past, cooling and its evidence. Why the Big Bang is not a firework, and what remains unknown about an ultimate beginning.
How do we know the Universe is expanding?
Spectral lines, independent distances and supernova light-curve durations: how observations test cosmic expansion, and why individual galaxies can approach us.
Why do we see distant galaxies as they were in the past?
Light brings earlier events with a delay. Distinguish light travel time, galaxy age and present distance in an expanding Universe.
What is the cosmic web?
How galaxies, gas and dark matter form nodes, filaments and voids, what sky surveys measure, and how a map differs from a simulation.
How do we measure the distance to another galaxy?
How Cepheids, geometric anchors and Type Ia supernovae transfer the scale along the cosmic distance ladder, and why standard candles require calibration.