negatives of space travel???????

Cost. You can't afford it. And probably never will.

:-)

It takes too long.

You have to bring a lot of baggage.

Cost
Deadly Environment for Humans
Time to get from one place to the next

we dont have the technology to travel faster than the speed of light, and since the distances are too great between galaxies, space travel is impractical for large distances. if my numbers are right, it would take us 400,000 years if we traveled at the speed of light to the nearest galaxy!

so to get around the universe we need to know how to go super fast.

1.) Confinement results in lack of normal exercise.

2.) Weightlessness results in muscle deterioration.

3.) Bone structures accustomed to working under the
weight loads caused by Earth's Gravity are suddenly
exposed to weightlessness and begin changing.

4.) In a closed atmosphere within a space ship, mold,
mildew, bacteria, and viruses could run rampant over a long flight time period. Under the conditions of weightlessness,
new, unknown varieties of bacteria could grow and overwhelm the spaceship occupants. Little knowledge from experience exists for this kind of "extended" space travel.

5.) Mission planners are lookinmg into some form of induced human hibernation, similar to what bears do in the winter, for reducing the food, water, and air intake requirements of space travelers. All of this research is a new frontier for scientists, and their work will be tested well before it is implemented.

6.) One or two years of confinement inside of a sardine can (space ship) could have detrimental effects on the mental stability of a crew. Further research is required.

One negativity is that you might change something in the past and make a impact on everyone.

For now -- We are of Type-0 civilization, and our technology is still backward for interstellar travel. We are not able to reach some distant part of the cosmos in ones lifetime.
For future -- When human technology will be able to propel crafts at the fractions of the speed of light, then the time dilation effect will be so high that one would go beyond his time and there won't be another way to get back to his present time.
The best time for space travel, will be only when we will be able to produce wormholes or even contracting and expanding space-time.