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rasa2013 t1_j8xqxwu wrote

It's a good question! This type of question (about the size of the universe and the speed of light) is one of the reasons why we developed a theory that the universe had a growth period we refer to as cosmic inflation.

In the very early universe, the universe expanded faster than the speed of light to become quite big. This doesn't break any laws of physics because space isn't a "thing" the way a photon or a calcium atom is a thing. It can expand faster than light moves. That is one of the reasons light speed is dwarfed by the size of the universe. The other reason, of course, is that the universe is very old. Billions of years is an amount of time our brains just don't comprehend.

https://en.wikipedia.org/wiki/Inflationary_epoch

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Mammoth-Mud-9609 t1_j8xqot2 wrote

Light isn't slow it is just the universe is mind bogglingly huge. Our Milky Way is part of a much larger group of stars known as the Local Group, which in turn is part of the Virgo Supercluster, there are a great many superclusters out there spreading out over our universe. https://youtu.be/ochPHsx8O88

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RobertLee2354 t1_j8xu7iy wrote

What was the point of this response lol? The Universe is big and light does move pretty slow in comparison to the scope of it. The correct answer is nobody really knows why the speed of light is the speed of light, and not faster or slower.

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left_lane_camper t1_j8y0hpo wrote

The speed of light is directly related to the permittivity (ε_0) and permeability (μ_0) of free space, via

c = ( ε_0 μ_0 )^1/2

as a consequence of building the wave equation from Maxwell's equations. Though whether this answer is in any way satisfying depends on whether one considers the speed of light or these other EM properties of free space to be more fundamental (and, in general, we usually define ε_0 and μ_0 with c as well, simply by re-arranging the equation above). But changing c would require changing one or both of these other fundamental constants as well.

My personal favorite answer, though, is when you ask someone who does GR or cosmology research about why the speed of light is what it is and they look at you like you have three heads and say "I don't know what you mean, the speed of light is exactly dimensionless 1".

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RobertLee2354 t1_j8z3gbt wrote

yup. that's why gravitational waves also move at the speed of light. thats the fastest anything can move through the fabric of space-time.

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breckenridgeback t1_j8xx4is wrote

Expansion of the Universe aside, the size of the observable Universe (the only "size of the Universe" we can really observe) is approximately the age of the Universe times the speed of light. (Expansion has increased it well beyond this value - it's about four times that - but it's still on roughly the same order of magnitude.) So a simple answer to your question is "the Universe is old, so light has had a long time to travel, so the most distant parts we can see are very far away".

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berael t1_j8xsrqs wrote

"Why are supersonic jets extremely slow in terms of the size of the Milky Way galaxy?" The two things don't have anything to do with each other.

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InternetAnima t1_j8xv53f wrote

Nah the cosmic limit for causality is certainly more fundamental than a plane. It's a perfectly valid question.

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metaphorm t1_j8xwme6 wrote

the answer to this question is also the answer to the question "why is the sky black at night?"

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space expands over time. the speed of light remains constant. the amount of space that light has to travel across gets larger over time.

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Safe_T_Cube t1_j8xyzdo wrote

As far as we know the universe is infinite, so anything moving any speed will be miniscule in comparison.

What you're thinking of is probably the observable universe, which itself is defined by the speed of light. You can only see light that has had enough time to travel from its source to your eye.

This means what you think of as the universe is defined as speed of light * the age of the universe. If that were the only factors it would always take you the lifetime of the universe to reach the edge of the observable universe while traveling the speed of light.

However the universe is also expanding, the universe is constantly moving away from you, faster then the speed of light for things far enough away. Because of that the universe is much bigger than just the speed of light times the age of the universe, it's roughly the speed of light * the age of the universe * the rate of expansion, so big that you will never be able to reach all that you can see (as far we understand).

It's kind of like asking why a second is so short in comparison to your entire life. Your life is constantly getting one second longer for every second that passes, but at the beginning there was a point where one second was your entire life. Not accounting for expansion, the radius of the observable universe gets one light second bigger every second, but at one point the "observable" universe was only one light second across.

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GreenHandbag2 t1_j8xzanx wrote

Ligth is very fast, precisely 299 792 458 m / s fast, even at those incredibly speeds it takes ligth 100,000 ligth years to cross our galaxy, ligth isn't slow, the universe is just mind bogglingly big.

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explainlikeimfive-ModTeam t1_j8xzike wrote

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urzu_seven t1_j8xytiu wrote

The simplest answer is because that’s the way the laws of the universe exist. The speed of light appears to be a fundamental property of the universe as we know it and that property is unrelated to how far across anything in the universe is.

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