I know that the universe is 13 billion years old and the fastest anything could be is the speed of light so if the universe is expanding as fast as it could be wouldn’t the universe be 13 billion light years big? But I’ve searched and it’s 93 billion light years big, so is the universe expanding faster than the speed of light?
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The Universe *is* expanding faster than the speed of light. The reason why is one of the fundamental questions that remain unanswered in physics today. Scientists have suggested the presence of dark matter to explain this phenomenon, however nothing has been proven yet.
The expansion of the universe doesn’t have a *speed*–speed depends on space (length) and it’s space that’s changing, so speed doesn’t make sense.
Expansion does have a *rate*, but it’s not measured in distance-per-time, it’s speed-per-distance. Specifically, 73.24 (km/s)/Mpc.
What that means is that *expansion* isn’t “moving” faster than light (that’s apples and snorkels), but **the distance between** two objects may be ~~moving *away from each other*~~ **increasing** faster than light.
Tl;dr: The “speed” of anything doesn’t make sense from the position of expansion because it’s space that is changing.
Exactly light speed. It is not expanding faster than light. The cosmic redshift can be entitely described as a Doppler shift+ gravitational redshift, there’s no need to introduce unphysical ideas like ‘space expanding’.
no. Hubble’s law.
expansion of the universe is happening on a cosmic scale, affecting the vast distances between galaxies. the rate of expansion is typically measured in units of kilometers per second per megaparsec (km/s/Mpc). This unit describes how fast objects are receding from each other over a given distance.
the accepted value for the Hubble constant is approximately 73.3 kilometers per second per megaparsec, which means that for every 3.26 million light-years of distance between objects, they are moving apart by about 73.3 kilometers per second. as described by Hubble’s law, is not constrained by the speed of light. The expansion rate is determined by the overall structure and content of the universe, including dark matter, dark energy, and ordinary matter.
I wanna ask an extra question!
Does the universe is expanding by stretching out? If so wouldn’t the distance between planets (eg. Distance between earth and sun) also stretch out? Or not what is it then?
No MATTER can ACCELERATE past the speed of light. The expansion of the universe is the SPACE between matter expanding, so no object is moving at all (not to mention FTL) with regard to its surrounding space.
It’s expanding at a rate of about 70km/s per megaparsec (which is the same as a frequency of once per 14 billion years, roughly)
If you assume this expansion rate is constant, this gives you a simple differential equation for a fixed position’s distance in terms of time. The details aren’t important, but it basically means that any region of space gets about e times wider (2.718… times wider) every 14 billion years. This is not necessarily a realistic model, because of the assumption, but it illustrates the idea.
On small scales (the size of galaxies) this has no effect, because things can easily move towards each other much faster than the universe can expand them apart. Gravity holds these things together.
On large scales (beyond small galaxy clusters) the rate of expansion wins out, and these distant galaxies are essentially dragged away by the receding space that they only move through so fast. On massive scales, even light moving towards us can no longer beat the expansion of space, giving a limit to how far we can ever see.
A recent study using gravitational lensing has provided what could be the best answer yet, though the answer in-and-of-itself is rather confusing.
The speed of universal expansion seems to be 46 miles per second per megaparsec (a megaparsec a distance of around 3.26 million light-years).
TLDR: There’s no real ELI% answer.
Digestible Source: https://www.sciencealert.com/we-saw-this-star-die-5-times-and-it-shows-how-fast-the-universe-is-expanding
Space time is considered to be a fabric.
So now assume there is piece of cloth and you stretched it out in a way that you can roll a marble (assume marble is light) across it as light travels, place some walnuts assuming those are galaxies. The light,it can only travel at a certain speed.
Now if you further stretch out the cloth, the distance between the walnuts will increase, but that is nothing to do with the marbles.
It doesn’t matter at what speed the marble is rolling, since the cloth itself is stretching out.
>wouldn’t the universe be 13 billion light years big?
Only if it exploded out of a single point within the universe. But the big bang wasn’t all the stuff exploding out of a point in space within the universe, it was an explosion of space. At t+1 nanosecond, space is infinitely big in every direction, all the stuff within it is just really tightly packed together. The big bang is how space expanded and all the stuff had enough room to cool off and form things like atoms.
> But I’ve searched and it’s 93 billion light years big,
That’s likely the **visible** universe. The parts of it we can see. And that’s bigger than 13 billion lightyears because when that early stuff that’s now 93 billion light years away emitted light ~13 billion years ago, it was a lot closer to us. The space between us grew.
>so is the universe expanding faster than the speed of light?
Yes. That part is true. Centered on us, there’s enough distance between us and the edge of the visible universe that the rate of expansion sums up to more than the speed of light. It means stuff on the edge is fading away and getting more and more feint. Matter is falling out of our cone of causality. Which really isn’t a perfect cone anymore, it’s more like a column, and its even getting narrower. Anything past that column, even if it launched itself right at us at the speed of light, like a flashbulb, the space between us grows faster than it travels.
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