Inspired by a quotation from J.B.S. Haldane, I would like to say that the Universe is not only bigger than we suppose, but bigger than we can suppose. Or perhaps I should say that it is bigger than we can fully comprehend.
The Universe is big. Really, really big. Frankly, it is hard to imagine how big it is, which is why so many people have little idea of its true size. I have been teaching astronomy in one form or another for 50 years, and I remain amazed at the difficult-to-comprehend distances involved. In this time I have learned that there are many, many misconceptions about space and the Universe, but probably the most common are misconceptions about size and distance.
I think a lot of students get very limited — if not downright incorrect — instruction on this in school, and then never pursue it any future, leaving that erroneous information embedded into their brains.
Not to mention the misleading graphics often found in elementary textbooks and educational material. Here is a section of a poster I had as a child on my wall long ago. It wildly distorts the distance. It makes the planets look as if they are right next to each other, when in fact they are separated by thousands of times their own diameters. For example, on average, Jupiter is separated from Earth by more than 5,000 times its own diameter!
To be fair, though, distances and sizes on a poster like this must be distorted to be seen. If you plotted the solar system out to Neptune on a 3-foot poster in proper scale, nothing could even be seen except perhaps a tiny dot for the Sun. We see them in the real sky because they are glowing against a black background.
Anyway, I’ve used many analogies to try and illustrate the topic of scale in the Universe. First off, imagine a hydrogen atom, which consists of a tiny positive proton and a negative electron. A hydrogen atom, which usually exists as part of a molecule rather than alone, is so small that it would take roughly 1.7 billion billion billion to equal an average human. The diameter of a hydrogen atom is about one picometer, which is one ten millionth of a millimeter, far too small to be seen even the best optical microscope.
Now, what if I told you that the Earth compares to the known Universe as a single hydrogen atom compares to a human? Pretty amazing, huh? Well, it’s absolutely wrong. The Universe is actually much, much bigger than that. (See note about the size of the Universe below.)
Actually, the Earth compares to the known Universe, roughly as a hydrogen atom compares not to a human, not to the entire planet Earth, but to the Sun!
The Sun is 109 times the diameter of Earth and in volume is more than a million times larger. So the Earth compares to the known Universe as a single hydrogen atom compares to the Sun. But that is just a rough comparison. Actually, the known Universe is about 43% larger. Let that sink in.
If you wish to check it yourself, here’s the data.
These figures are rounded a bit, but you should be able to see clearly that the two ratios are in the same order of magnitude (signified by the E+19, which means 10 to the 19th power!).
Within the uncertainties inherent in the data and assumptions, the ratios are essentially the same. I assume a diameter of the known universe to be twice the light time distance to the observable boundary, which makes it 27.6 light years across, or about 2.6 times 10^29 millimeters. Truth is, the Universe is actually much larger than this, and perhaps even infinite, as explained in the note below.
So indeed, the Universe is really, really big. It is so big, in fact that the only way that any of use can begin to comprehend is through a little math.
NOTE: To make this more palatable, I have made some simplifications that really do not affect the overall validity of the piece. There is a good bit of variation in the way words are used, but I have used the term “known” or “observable” Universe to refer to that part of the Universe that extends out to 13.8 billion light years in all directions. That distance, 13.8 billion light years, is the light time limitation of radiation that left near the time of the Big Bang. We can directly observe objects near that boundary, but only as they were that far back in time. So I have considered that distance as the boundary, and the known universe to be sphere of 13.8 billion light years, centered on Earth.
I did this for simplicity. However, it poses two non-trivial problems. First off, everything we can detect near that 13.8 billion light year boundary was moving away from us at that time, so consequently, even though we can observe it only as it was 13.8 billion years ago (Because of the restriction of the Speed of Light), it is actually much farther away now. In fact, most current estimates are that it is about 46 billion light years away, and hence the “known” Universe is at least 37 times the size (volume) larger.
You might think that this violates Relativity and the restriction of the speed of light. But it doesn’t. Those restrictions do not apply to space itself. The dimensions of space can increase much faster than the speed of light and Einstein would be just fine with that.
The second problem is that we tend to imagine the Universe as a big sphere. That is because the limit of our vision, the “cosmic horizon” is at the same distance all around us. Imagine being at the center of a basketball, where the inside edges of the balloon are all at a set distance (around 4.7 inches!) all around. You would think that the Universe is spherical because that would be how it would appear to you. You could not see beyond it, but that would not mean the there was nothing beyond it, or necessarily that whatever lay beyond your observable Universe was spherical.
Furthermore, by definition, the Universe is “everything.” In order to properly define the shape of the Universe, you would have to get outside it. But because anywhere you could go would still be inside the Universe — it’s everything, you know — that would be impossible.
J.B.S. Haldane reference: http://bit.ly/39znfsT