No known laws of physics prohibit spaceflights to the stars. However, conventional technical and scientific wisdom holds that interstellar spaceflight is practically not feasible.
One of the major obstacles are the huge distances an interstellar craft should cover: Proxima Centauri, the closest stellar neighbour to our Sun as known today, is about 4,24 light years away, which is about 6.800 times the distance to Pluto.
To overcome these distances we need new propulsion methods - today's rockets cannot do the job -, new energy supply systems for onboard instrumentation, proper shielding against interstellar material and radiation during a mission, to name but a few difficulties.
Solid technical development is already on the way: now scientists and engineers are looking at realistic missions which would go ten times farther than Pluto in merely 30 years. There are even thoughts about possible near-term technologies which could push the velocity with another factor 10, leading to travel times of around 2000 years for a Centauri Mission. There is also a rapid development in nanotechnology and AI, both enablers for interstellar travel.
Various motivations exist to embark on an interstellar endeavour, including the seemingly ever-existing challenge of the stars and arising fears about possible near-term existential risks for humanity, to list the two extremes.
The Internet has channelled enormous power into collaborative work in a historically unprecedented way. For example, it has already helped in forming of numerous new organizations which aim at long term thinking, inclusive this Long Bet site. Within these, web-based interstellar advocate groups - like Centauri Dreams, the Tau Zero Foundation and peregrinus interstellar - are growing. I believe that such a collective power of Earth's citizenship, together with fast technical development and compelling motivation as mentioned above, will support the birth of the first interstellar mission soon.
The laws of physics as presently understood make interstellar flight a possibility (I believe it is inevitable), but a tremendously difficult one. Barring a near-term breakthrough, we will still be working within the parameters of these laws in 2025, substantially aided by nanotechnology and developments in computer science, to be sure, but still running up against the inexorable limitations imposed upon us by Special Relativity. While I believe a true interstellar mission will be launched at some point, I will argue that it will not be launched within this century, and that when it is launched, it will take advantage of the numerous advances in engineering that will have taken place by that time to allow it. The 2025 time frame is joyously optimistic, and I would support it if I could. But Tibor and I both believe that continuing to work for the interstellar goal -- and continuing to debate it in forums like these -- is worthwhile in itself, and I think we'll both be happy if the loser's money winds up in the hands of an organization that actively promotes these goals.
We agree that:
1) The mission can be a manned or unmanned flyby probe or to be captured by the target star's gravitational field. It will have been designed expressly as a mission to another star, and not an outer-Solar System mission that keeps going.
2) Allowed launch location of the spacecraft is any place in the Solar system within the orbit of Neptune, either from the surface of a solar system body or from any orbital position.
3) As a minimum requirement for the mission the spacecraft shall be capable to deliver data for at least one scientific measurement.
4) Planned mission duration shall be less than 2.000 years.
The statement "widely supported by the public" might be e.g. assessed by an outreach action in which at least 1.000.000 (one million) votes must be gathered in favour of the mission. Voting can start earliest at the announcement time of the mission baseline design; end date of voting is the launch date. The mission team will be responsible to ensure that such a voting can take place; it can cooperate with other projects or organizations to set up the voting procedure. Reasonable effort will be done to ensure that one person should only vote once. Should there be in the meantime a prize contest organized where the prize win conditions are compatible with our betting terms, this will be interpreted to be a wide support as well.
However, we agree that the proviso for the wide support is not a necessary condition to decide the outcoume of the bet.