Great overall, but I disagree with this “while colonization would insulate us against a number of potential existential risks, there are some risks that it wouldn’t stop. A physics disaster on Earth, for example, could have consequences that are cosmic in scope. For example, the universe might not be in its most stable state. Consequently, a high-powered particle accelerator could tip the balance, resulting in a ‘catastrophic vacuum decay, with a bubble of the true vacuum expanding at the speed of light.”’
If a positive singularity occurs and the solution to the Fermi paradox is that we are alone I would like to make a copy of myself and put that copy on a spaceship that travels fast enough away from earth so that (given sufficient time) when you add in the expansion of the universe something starting at earth and traveling at the speed of light would not be able to reach me. As I understand it, once I have traveled far enough from earth it will be impossible for something from earth to reach me regardless of my speed.
I’ve seen this claim many places, including in the Sequences, but I’ve never been able to track down an authoritative source. It seems false in classical physics, and I know little about relativity. Unfortunately, my Google-Fu is too weak to investigate. Can anyone help?
Because this expansion is caused by relative changes in the distance-defining metric, this expansion (and the resultant movement apart of objects) is not restricted by the speed of light upper bound of special relativity.
Thank you. It is moderately clear to me from the link that James’ thought-experiment is possible.
Do you know of a more authoritative description of the thought-experiment, preferably with numbers? It would be nice to have an equation where you give the speed of James’ spaceship and the distance to it, and calculate if the required speed to catch it is above the speed of light.
Naively, the required condition is v + dH > c, where v is the velocity of the spaceship, d is the distance from the threat and H is Hubble’s constant.
However, when discussing distances on the order of billions of light years and velocities near the speed of light, the complications are many, not to mention an area of current research. For a more sophisticated treatment see user Pulsar’s answer to this question …
Yes, until the distance exceeds the Hubble distance of the time, then the light from the spaceship will red shift out of existence as it crosses the event horizon. Wiki says that in around 2 trillion years, this will be true for light from all galaxies outside the local supercluster.
Great overall, but I disagree with this “while colonization would insulate us against a number of potential existential risks, there are some risks that it wouldn’t stop. A physics disaster on Earth, for example, could have consequences that are cosmic in scope. For example, the universe might not be in its most stable state. Consequently, a high-powered particle accelerator could tip the balance, resulting in a ‘catastrophic vacuum decay, with a bubble of the true vacuum expanding at the speed of light.”’
If a positive singularity occurs and the solution to the Fermi paradox is that we are alone I would like to make a copy of myself and put that copy on a spaceship that travels fast enough away from earth so that (given sufficient time) when you add in the expansion of the universe something starting at earth and traveling at the speed of light would not be able to reach me. As I understand it, once I have traveled far enough from earth it will be impossible for something from earth to reach me regardless of my speed.
I’ve seen this claim many places, including in the Sequences, but I’ve never been able to track down an authoritative source. It seems false in classical physics, and I know little about relativity. Unfortunately, my Google-Fu is too weak to investigate. Can anyone help?
Do you mean the metric expansion of space?
https://en.wikipedia.org/wiki/Metric_expansion_of_space
Thank you. It is moderately clear to me from the link that James’ thought-experiment is possible.
Do you know of a more authoritative description of the thought-experiment, preferably with numbers? It would be nice to have an equation where you give the speed of James’ spaceship and the distance to it, and calculate if the required speed to catch it is above the speed of light.
Naively, the required condition is v + dH > c, where v is the velocity of the spaceship, d is the distance from the threat and H is Hubble’s constant.
However, when discussing distances on the order of billions of light years and velocities near the speed of light, the complications are many, not to mention an area of current research. For a more sophisticated treatment see user Pulsar’s answer to this question …
http://physics.stackexchange.com/questions/60519/can-space-expand-with-unlimited-speed/
… in particular the graph Pulsar made for the answer …
http://i.stack.imgur.com/Uzjtg.png
… and/or the Davis and Lineweaver paper [PDF] referenced in the answer.
Wow. It looks like light from James’ spaceship can indeed reach us, even if light from us cannot reach the spaceship.
Yes, until the distance exceeds the Hubble distance of the time, then the light from the spaceship will red shift out of existence as it crosses the event horizon. Wiki says that in around 2 trillion years, this will be true for light from all galaxies outside the local supercluster.