The size and price of the accelerator. For example, aliens have an accelerator which could send 1mg probe every second, and the accelerator’s weight is 1000 tons. Thus, it will send its own mass in 20 000 years. All these probes clump (using some internal navigation and small difference in initial speed) with each other after a few million years, and using some nanotech, they build another accelerator, which send just one probe in the back direction, which is the deceleration, as its speed will be zero.
To send all the probes simultaneously, one need to build a trillion of such accelerators. However, this seems to be achievable even with one Dyson sphere. So clumping make sense only if there are some limits on the size of the accelerators.
Also, any intergalactic probe will experience “natural” deceleration because of expanding universe, similar to red shift, so the back-accelerator may be small than the sending accelerator.
The size and price of the accelerator. For example, aliens have an accelerator which could send 1mg probe every second, and the accelerator’s weight is 1000 tons. Thus, it will send its own mass in 20 000 years. All these probes clump (using some internal navigation and small difference in initial speed) with each other after a few million years, and using some nanotech, they build another accelerator, which send just one probe in the back direction, which is the deceleration, as its speed will be zero.
To send all the probes simultaneously, one need to build a trillion of such accelerators. However, this seems to be achievable even with one Dyson sphere. So clumping make sense only if there are some limits on the size of the accelerators.
Also, any intergalactic probe will experience “natural” deceleration because of expanding universe, similar to red shift, so the back-accelerator may be small than the sending accelerator.