Impossible Thought: Galaxy Traveling at Light Speed, Milky Way Merging/Ripping

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If a galaxy were to approach the Milky Way at the speed of light, the planet would be destroyed instantly without any prior warning. The discussion emphasizes that massive objects, like galaxies, cannot travel at light speed, and typical galaxy velocities are much lower. The idea of not knowing about such a galaxy due to its speed is highlighted, suggesting that if this scenario were real, humanity would already be gone. The conversation also touches on the speculative nature of these thoughts, with a reminder to adhere to forum rules against overly speculative posts. Ultimately, the thread reflects on the absurdity of the scenario while cautioning against trolling.
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If another galaxy were to be traveling towards us at the speed of light and as well as the Milky Way being ripped apart or merged, our planet were to suffer a direct hit, we would never know about it! Gone in an instant!

Also, we would not know, or do not know, of the existence of such a galaxy because of its speed.

So, if this does not appear on this forum, it's already happened and none of us are here!
 
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Hi AncientBrit; welcome to PhysicsForums.
Please consult the rules, specifically the section on Overly Speculative Posts.

No massive objects can travel at the speed of light---especially a galaxy. The relative velocities between galaxies tends to be fairly moderate---generally 100's of km/s---and far below the speed of light.
 
AncientBrit said:
If another galaxy were to be traveling towards us at the speed of light and as well as the Milky Way being ripped apart or merged, our planet were to suffer a direct hit, we would never know about it! Gone in an instant!

Also, we would not know, or do not know, of the existence of such a galaxy because of its speed.

So, if this does not appear on this forum, it's already happened and none of us are here!

If I were to become the supreme being of all the multiverse and then erase all of humanities memories and it wasnt on this forum then its already happened!

Also this could mean... sorry I got distracted by the blue and yellow spotted dwarf piglet flying past the window.

Please don't post rubbish. **Awaits thread locking**
 
I wasn't aware that people trolled on PF. Hah
 
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
Why was the Hubble constant assumed to be decreasing and slowing down (decelerating) the expansion rate of the Universe, while at the same time Dark Energy is presumably accelerating the expansion? And to thicken the plot. recent news from NASA indicates that the Hubble constant is now increasing. Can you clarify this enigma? Also., if the Hubble constant eventually decreases, why is there a lower limit to its value?
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