Thought Experiments

Questions about the expansion of the universe?

Measurements of the rate of expansion of the universe have shown that more distant galaxies are moving away from the Milky Way at a faster rate. From this, it has been concluded that the universe is expanding at an accelerating rate. However, as so-called dark energy has never been directly detected, I have been thinking about the following:

My thoughts:

  1. 1. Linear expansion (using the hand as an example):

    Let's first look at a simple example that everyone can understand: take a hand and spread the fingers. Viewed from the little finger, the middle finger moves further away from it than the ring finger, and the index finger moves even further away. Since all the fingers move at the same time, we can conclude that the fingers further away move away from the little finger more quickly.

On closer inspection, however, one realises: The middle finger itself does not move – only the other fingers move away from it. This is not immediately apparent when viewed from the little finger. The same principle can be seen when stretching a rubber band with evenly spaced markings: All sections stretch at the same rate. If you look closely, you will see that all sections expand outwards from the centre of the band.

Due to the expansion, each section begins where the previous one ends. This creates the impression of an accelerated expansion – even though all sections are in fact expanding at a uniform rate. This phenomenon occurs with any positive expansion, even if the rate of expansion slows down.

Analysis of the distances between points from the left-hand starting point:

Time Point 1 Point 2 Point 3 Point 4 Point 5 Point 6
(Center)
Point 7 Point 8 Point 9 Point 10 Point 11
t₀ 0 30 60 90 120 150 180 210 240 270 300
t₁ 0 36 72 108 144 180 216 252 288 324 360
t₂ 0 42 84 126 168 210 252 294 336 378 420
t₃ 0 48 96 144 192 240 288 336 384 432 480
t₄ 0 54 108 162 216 270 324 378 432 486 540

Note: The values show the distances of the 11 points from the left-hand starting point (point 1). Point 6 (the center point) always remains in the center of the field, and the extent is measured from there.

It can be seen that the individual points move away from their neighbouring points by the same distance and at the same rate. Points further away therefore cover greater distances. As the expansion takes place simultaneously everywhere, it appears to be accelerating from the perspective of the individual points.

Is this not a fundamental property of every extension?

This raises the question: Is any additional energy required for this effect at all, or does it arise solely from the expansion itself?

Let us now consider a circle. Here, the outward extension follows the same principle. However, the segments along the circumference of the circle extend differently from the radial distances from the centre outwards. Since the circumference of a circle is defined by the formula π × diameter, the length of the segments changes according to the formula: (diameter × π) / number of segments .

Let's look at a circle. Here, the outward expansion follows the same rule. However, the segments along the circumference of the circle change differently from those in the movement from the centre outwards. Since the circumference of a circle is given by the formula diameter times π, the lengths of the segments change according to the formula: diameter times π divided by the number of segments.

Distances of the circle points from the top point:

Diameter Point 1
(top)
Point 2 Point 3 Point 4 Point 5 Point 6 Point 7
(bottom)
Point 8 Point 9 Point 10 Point 11 Point 12
200 0 52 100 141 173 190 200 190 173 141 100 52
240 0 62 120 169 207 228 240 228 207 169 120 62
280 0 73 140 196 239 266 280 266 239 196 140 73
320 0 83 160 224 277 312 320 312 277 224 160 83
360 0 94 180 252 306 342 360 342 306 252 180 94

Note: The values show the distances of the 12 points from the topmost point (point 1). Point 7 is the lowest point. The diameter corresponds to the maximum distance (point 1 to point 7).

The points are shifted outwards from the centre, moving away from the centre at a specific angle. The distances between the individual points can be calculated using the law of sines. The animation illustrates that, as the circle expands, the distances between the points depend on the change in the circumference.

This page contains interactive visualizations of the expansion of the universe. All animations can be controlled using the keyboard.