According to Einstein, a lot of energy is needed as a spacecraft nears the speed of light.
Therefore,

1. If Einstein is correct, it will be impossible for humans to travel at the speed of light.

2. If Einstein is correct, it would be impossible for humans to travel at the speed of light.

3. If Einstein were correct, it would be impossible for humans to travel at the speed of light.

What are the differences among the following sentences if all of them are correct?

According to Einstein, a lot of energy is needed as a spacecraft nears the speed of light.
Therefore,

1. If Einstein is correct, it will be impossible for humans to travel at the speed of light.

2. If Einstein is correct, it would be impossible for humans to travel at the speed of light.

What are the differences among the above sentences if both are correct? Because I wonder if it is possible to use "would" in the main clause while the conditional clause is a present tense?

According to Einstein, a lof of energy is needed as a spacecraft nears the speed of light. Therefore,

1. If Einstein is correct, it will be impossible for humans to travel at the speed of light.

2. If Einstein is correct, it would be impossible for humans to travel at the speed of light.

3. If Einstein were correct, it would be impossible for humans to travel at the speed of light.

According to Einstein, a lot of energy is needed as a spacecraft nears the speed of light.
Therefore,

1. If Einstein is correct, it will be impossible for humans to travel at the speed of light.

2. If Einstein is correct, it would be impossible for humans to travel at the speed of light.

3. If Einstein were correct, it would be impossible for humans to travel at the speed of light.

What are the differences among the following sentences if all of them are correct?