The age of the Universe is 13.8 billion years.

Our Solar System was created 4.6 billion years ago. For the purpose of this presentation let's call it the Solar System Birth (SSB). It began when the Universe was ²⁄₃ of its current size. What if our Solar System was also created at ²⁄₃ of its current size? Is the expansion of the Universe all‑encompassing? Let us consider what would happen if the Solar System expanded in the same way, increasing at the same rate.

Won't the force of gravity override any expansion? Isn't our Solar System "gravitationally bound"? The "truly bound" structures are kept together by the electromagnetic force.
And no, gravity is not a force; it is a curvature of spacetime, and as the Universe expands, so does the curvature of spacetime.

Credit: NASA

At the time of the formation of the planets, Mars was in the true Goldilocks zone as its semi-major axis was then 1.0 au. This is now Earth's orbit, when the Sun was 70% as bright as it is today. How does the Sun's distance affect each planet's sunlight? They would have received 1.5² = 2¼ more sunlight per area falling on the planet.

The following table shows the amount of solar energy that currently reaches the outer atmosphere of each planet. Consider the solar energy at the SSB. There are two factors to consider. The smaller size of the Solar System by one third as well as the faint young sun hypothesis(fys). For example, Mars now gets 588 watts/_m² but at the SSB the solar energy was 930 watts/_m².

The planets of the Solar system

planet ∗	semi‑major axis at the SSB in au	solar energy in watts/m² at the SSB	adjusted for fys hypothesis solar energy in watts/m² at the SSB	semi‑major axis now in au	solar energy now in watts/m²
Mercury	0.258	20,250	14,175	0.387	9,000
Venus	0.482	5,850	4,095	0.723	2,600
Earth	0.667	3,060	2,144	1.000	1,360
Mars	1.0	1,323	930	1.5	588
Jupiter	3.469	112	80	5.203	50
Saturn	6.358	34	24	9.537	15
Uranus	12.794	8.3	5.8	19.191	3.7
Neptune	20.0	3.4	2.4	30.0	1.5

Kepler's Third Law: the squares of the orbital periods of the planets are directly proportional to the cubes of the semi-major axes of their orbits.

How many days were there in a year on Earth at the SSB?
According to Kepler's third law, a shorter orbit would be only 1.5^-1.5 = 0.544 times as long, which means for Earth a reduction from 365 to 199 days in a year and for the moon a reduction from 27 to 15 days in a month.
We are assuming the rotation of the Earth being 24 hours long.

The Earth‑Moon system

Earth‑Moon system ∗	orbital period at the SSB	orbital period now	orbital period 4.6 billion years in the future
Earth	198.8 days	365.25 days	671.0 days
Moon	14.9 days	27.3 days	50.0 days

The moon distance is now 384,400 km, at the SSB it was at a distance of 256,000 km, at the which was the genesis of our Solar system. The distance to the moon was closer by 128,000 km, and since the genesis, it calculates out to an increase of 2.8 ^cm⁄_year. The observed increase of the Earth‑Moon distance is 3.8 ^cm⁄_year; The other 1.0 ^cm⁄_year is due to gravitational interactions from Earth's ocean tides. The Earth-Moon distance would be 46,000 km closer. This suggests that the increasing Earth‑Moon distance is ¼ tidal forces and ¾ universe expansion.

Credit: NASA

This table goes back to the SSB and describes the amount of sunlight reaching the Earth from the Sun.

The first column shows how far back in time the period that we examine.

The second column shows the length of earth's semi-major axis in billions of metres.

The third column is the amount of calculated sunlight received with an increasing output from the Sun. According to the Faint Young Sun hypothesis, it is assumed to have a value of 70% at the SSB, and now has a value of 100%. Over this range we are assuming a linear increase in luminosity.

The fourth column is the amount of sunlight reaching Earth based on the increasing distance of the Sun due to the expansion of the Solar System.

The fifth column is simply multiplying the third and fourth columns to produce the effective sunlight. This shows that the effective sunlight was 57% greater at the SSB than it is today. That includes Mars as well.

The sixth column is the sunlight reaching the Earth if the Sun's output was constant.

The seventh column has been adjusted, allowing for the amount of sunlight being emitted from a cooler Sun to a warmer Sun.

The eighth column shows certain events, such as when the Jovian planets form.

Earth in an expanding Solar System

Billions of years ago ∗	au in Gm	Faint Young Sun hypothesis	Expansion Factor	Effective Sunlight	Earth solar energy watts/m²	Solar energy Adjusted by Faint Young Sun hypothesis	Earth Events
4.6	100	0.700	2.25	1.575	3,062	2,144	Solar System Birth
4.59	100	0.701	2.245	1.573	3,056	2,141	Jovian planets form
4.55	101	0.706	2.226	1.565	3,029	2,130	Sun fuses Hydrogen
4.5	101	0.707	2.202	1.557	2,997	2,117	Terrestrial planets form
4.4	102	0.713	2.155	1.537	2,933	2,092	HCN arrives on Earth
4.2	104	0.726	2.066	1.500	2,812	2,042	LUCA appears on Earth
3.85	108	0.749	1.924	1.441	2,618	1,961	More life appears
3.2	115	0.791	1.695	1.341	2,307	1,826	Cyanobacteria emerge
1.5	134	0.902	1.259	1.136	1,713	1,545	Mitochondria appear
0.54	144	0.965	1.083	1.045	1,474	1,422	Cambrian explosion
0.0	150	1.0	1.0	1.0	1,361	1,361	The Present

Mars in an expanding Solar System

Billions of years ago ∗	au in Gm	Faint Young Sun hypothesis	Expansion Factor	Effective Sunlight	Mars solar energy watts/m²	Solar energy Adjusted by Faint Young Sun hypothesis	Mars Events
4.6	150	0.700	2.25	1.575	1,328	929	Solar System Birth
4.59	150	0.701	2.245	1.573	1,324	928	Jovian planets form
4.55	151	0.703	2.226	1.565	1,313	924	Sun fuses Hydrogen
4.5	152	0.707	2.202	1.556	1,299	918	Terrestrial planets form
4.0	160	0.739	1.983	1.466	1,170	865	Extensive volcanism
3.7	165	0.759	1.867	1.416	1,101	835	Extensive water outflow
3.5	168	0.772	1.795	1.386	1,059	817	Slow iron‑oxidation
3.0	176	0.804	1.633	1.313	963	775	Loss of atmosphere
0.0	225	1.0	1.0	1.0	590	590	The Present

These are extraordinary claims. Yet, they acknowledge basic questions.

First, about the late start of life on Earth. At the time of genesis, the Earth was then closer to the Sun than Venus is now, possibly too hot for life to begin. Some theories suggest very cold, even freezing, conditions might have been beneficial for concentrating key precursors such as hydrogen cyanide (HCN) and promoting their polymerization into nucleic acid bases. Earth may have had to move further from the Sun so that the needed cooler temperatures could support life.

Second, this explains why Mars had a warmer and wetter atmosphere. It has features, such as riverbeds, lakebeds, and even ocean beaches, as well as a newly located vast underground reservoir of liquid water deep below its surface. This indicates a past climate in which temperatures were above freezing, allowing liquid water to exist on its surface.

Third, the current rate of the Moon's recession is considered unusually high. Earth's geological past calculates the recession primarily through the analysis of tidal rhythmites and growth patterns in ancient fossils, which provide physical evidence for a shorter day length and a closer moon in the distant past. This 1.0 ^cm/_year figure is an estimate for the average recession rate of the Moon.

Fourth, this solves the Faint Young Sun paradox, first introduced in 1972 by Carl Sagan and George Mullen. As the Sun evolved, its brightness was 70% of what it is today. So, why was Earth not frozen? The expansion of the solar system shows that early Earth was closer to the Sun and actually received 1.575 times more solar energy per square metre hitting the Earth's upper atmosphere than today. This may have been too hot for a snowball Earth. As for Mars it started losing its atmosphere three billion years ago when its solar radiation was 30% higher than it is today.

Fifth, this is the reason for the outward migration of the planets. There is no need to explain the migration of Uranus and Neptune by postulating 'gravitational attraction' by unspecified masses. There is also the Nice Model: The leading model for our solar system's evolution suggests the gas giants started in a more compact configuration (true). Jupiter, Saturn, Uranus and Neptune migrated significantly outward to their current positions, scattering a disk of planetesimals in the process. This model assumes that the inner rocky planets (Mercury, Venus, Earth and Mars) have also migrated outward at the same rate.

∗ All calculation errors are my own.

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Tuomo Suntola 2025
J. Phys.: Conf. Ser. 2948 012003

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J. Phys.: Conf. Ser. 1466 01200

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Proceedings of the International Conference