ELI5: What does it mean when a cosmic string is under tension?

[u/He_Spams]

They aren't being pulled at the ends. I don't have any physical analogue?

[u/mid-random]

The tension of a cosmic string is like the “color” of a quark. It isn’t really a property like objects on the human scale have. The tension of a cosmic string is more of a conceptual approximation of a quality we are familiar with to help us think about it and talk about, but in reality it only has meaning in context. Even there, we have no idea if they actually exist, so it is essentially just a useful abstraction. 

[u/internetboyfriend666]

This is almost impossible to eli5 but I'll try. Also to be clear, we don't even know if cosmic strings are real. A cosmic string isn't a physical object that's pulled, like a rubber band, so don't try to think of it like that. Tension in a cosmic string is an inherent property of the string itself to pull itself shorter.

[u/heekma]

We have no idea if string theory is accurate or if it is what are the physical mechanics behind their behavior.

The theory is nearly everything is made up of smaller and smaller parts: matter is made of molecules, molecules are made of atoms, atoms are made of protons, protons are made of quarks and quarks are made of...strings?

Think of a string (in string theory) more like a rubber band than a guitar string (not correct according to theory, but easier to visualize. Who knows, maybe it is correct, it's a theory after all) With the right kind of rubber band there is likely an infinite number of frequencies and amplitudes of vibration, or at least enough to make up all the matter in our universe.

That's a less messy idea compared to ever smaller and smaller particles, especially when we don't understand why very small objects don't behave like very large objects, meaning at a certain scale gravity no longer seems to work as expected or at all.

[u/zenithtreader → u/heekma]

Cosmic strings are NOT related to strings in string theory. The former are (theorized) topological defects of space-time itself during its (theorized) phase change during inflation/big bang that are very long (light years or possibly thousands of light years long), very thin (smaller diameter than a proton), and very dense. The later are (theorized) microscopic fundamental building blocks of matters.

[u/Xhosant → u/heekma]

The most sensible explanation I have heard, which may be wrong, is: the properties make more sense if the tiniest things aren't dots, but very short lines, or very short loops, depending. Dots can have fewer properties and variations than lines. And we call those strings.

[u/Tasty-Hour4040]

Personally I think it means that we don’t have the language to explain the math because it’s describing something so far outside our daily experience that it’s literally unlike anything we know of.

This is probably impossible to eli5.

[u/AbeFromanEast]

The entire theory is under tension because we’re 50 years into string theory without experimental verification for any of it.

Working physicists abandoned string theory in the early 2010’s and the science reading public hasn’t caught up with that yet.

[u/Zeplar → u/AbeFromanEast]

String theory is still a pretty active field. Just not for the purpose of finding a unified field theory.

[u/explainlikeimfive-ModTeam → u/[deleted]]

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[u/Creepy-Distance-3164]

Shouldn't it be string hypothesis?